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TLR;
Running issues with FS85X
Current main issue is that it hangs down load. Lean out L mix screw, idle falls until it's about to stall, but if I enrichen the L mix screw, it revs up again. Seems to be no happy medium.

Backstory:

Last year I saw a used Stihl FS85X on craigslist.

XXXXXtreme!
Fun fact: After MUCH searching I eventually determined that "FS85X" turns up zero results. It's actually an "FS85 RX". R meaning loop handle, and the X means it's the "lightweight version" with the low-interia hollow-center shaft. Shaves 0.5lbs off, while revving higher, but the trade-off is you cannot use the gearbox attachments with the hollow shaft.

It was $60, delivered!
Started easily, idled well, ran perfect.

I used it probably ~2 hours in total. No issues. Very lightweight and revved quite fast compared to my other trimmers (must be that XXXtreme thing). Surprised it's a 25.4cc.

I stopped using it because I felt it was too peak-y and preferred my Echo 266.

I went to use it 2-3 weeks later, and it wouldn't run, at all.
It was stored in a damp garage w/tendency to flood. Most stuff developed spiderweb-like mildew on bottom 6in, this trimmer included.

This season I worked on it.
Cleaned up mildew and dried oil gunk on lower case.
New fuel (tank and purged carb).
Visually inspected the cylinder. Looked great.

Started and idled--- did not tinker with carb.

Re-visit, and it'll cough over once or twice but won't run.
Took carb apart thinking float was to blame.
Idles, but it will not rev.

I re-set L/H mix screws.
All the way CW, and then follow markings on the shroud.

It will not run at the suggested 1 turn CCW for L, and 3/4 turn CCW for H.
I do my own thing to get it tuned down low, and I eventually get it to idle for long periods of time.
I check spark plug and coil gap. Both needed adjustment.

I adjusted the high mix until it revved well and used it for 10mins, 80% of time at full throttle while cutting grass with the string fully extended.
I tried to adjust the H screw while in use. I would wind it up, and hear it missing very slightly at max speed, so I enriched the H mix. Not sure if this is correct.
I couldn't get the d-d-d-d-d-w-w-w-wah-wah-wah-WAH-WAHHH-WAHHHH-WAHHHHHHHHH out of it though like in some carb adjust videos.

Then I realized it won't 'settle' down. The idle screw wasn't touching, so it must be too rich down low.

If I lean out the mix, it doesn't respond for ~1/4 turn, then it settles down. I stop. Then it starts to die. I enrichen it the smallest increment I can, and then it's "hanging" again, idling too high.
I've tried 'dancing' with it so many times, I'm convinced there's an internal carb issue such as a broken diaphragm or etc.

A stiff diaphragm makes the engine unresponsive or just sluggish
A torn diaphragm usually makes the engine flood all the time.

Before you start, slacken off the cable.
The throttle Butterfly ( or drum ) must be able to close fully.
And the trigger must be able to get the throttle Wide open.

You set the H needle by running the engine WFO and finding the spot where it starts to die from being too rich and then the other way for too lean
You then set the needle 1/2 way between the two extremes , erring slightly to the rich side.
This MUST be done with a full length of line hanging out the head.

Now the tricky bit .
Back off the throttle slowly and listen to the engine to see if it dies too rich or too lean as you get to the last 1/4 of trigger travel.
On most carbs the throttle stop screw can be used for this which frees one hand.
From here on in, it is just a matter of backing off the throttle stop a small amount, then doing the same thing with the L needle as you did with the H needle
Keep repeating till you get the engine idling smoothly.
If there is a sudden massive change, then you have just found the cross over H to L jet point so don't worry about it just continue till you get a nice idle.

Now that it is working nice, you have to stuff it up by readjusting the H needle because adjusting one will also affect the other.
Following this, readjust the L needle.
If you were in the ball park then it should remain running and it will be just a simple adjustment of the L
Now that the engine has a smooth idle, if the head is turning back off the throttle stop till it just stops then readjust the L needle.

If it needed a big adjustment ( 1/2 turn or more ) the you will have to go back to the H again and work your way down again.

Now the caveat.
If turning either needle 1 full turn makes no difference then that jet is probably blocked so the carb will need a proper clean.
If you pull a carb apart you MUST replace the gaskets.
The diaphragms can be reusd if they are OK but the gaskets will have compressed so their ability to make an air tight seal is highly compromised.
SO any of those U-Tube monkeys that show themselves reusing the old gaskets have absolutely no idea about what they are doing and are just posting to inflate their own egos.
Now if these clowns can not understand that a compressed gasket might not be able to reseal how much understanding do you think that have about any other vomit that came out of their mouths.

Pop off pressure is the same.
Any video that instructs you to pressureise the diaphragm till the needle pops off and the pressure suddenly drops has ZERO knowledge about what they are flapping their gums over.

bertsmobile1 said:

A stiff diaphragm makes the engine unresponsive or just sluggish
A torn diaphragm usually makes the engine flood all the time.

Before you start, slacken off the cable.
The throttle Butterfly ( or drum ) must be able to close fully.
And the trigger must be able to get the throttle Wide open.

You set the H needle by running the engine WFO and finding the spot where it starts to die from being too rich and then the other way for too lean
You then set the needle 1/2 way between the two extremes , erring slightly to the rich side.
This MUST be done with a full length of line hanging out the head.

Now the tricky bit .
Back off the throttle slowly and listen to the engine to see if it dies too rich or too lean as you get to the last 1/4 of trigger travel.
On most carbs the throttle stop screw can be used for this which frees one hand.
From here on in, it is just a matter of backing off the throttle stop a small amount, then doing the same thing with the L needle as you did with the H needle
Keep repeating till you get the engine idling smoothly.
If there is a sudden massive change, then you have just found the cross over H to L jet point so don't worry about it just continue till you get a nice idle.

Now that it is working nice, you have to stuff it up by readjusting the H needle because adjusting one will also affect the other.
Following this, readjust the L needle.
If you were in the ball park then it should remain running and it will be just a simple adjustment of the L
Now that the engine has a smooth idle, if the head is turning back off the throttle stop till it just stops then readjust the L needle.

If it needed a big adjustment ( 1/2 turn or more ) the you will have to go back to the H again and work your way down again.

Now the caveat.
If turning either needle 1 full turn makes no difference then that jet is probably blocked so the carb will need a proper clean.
If you pull a carb apart you MUST replace the gaskets.
The diaphragms can be reusd if they are OK but the gaskets will have compressed so their ability to make an air tight seal is highly compromised.
SO any of those U-Tube monkeys that show themselves reusing the old gaskets have absolutely no idea about what they are doing and are just posting to inflate their own egos.
Now if these clowns can not understand that a compressed gasket might not be able to reseal how much understanding do you think that have about any other vomit that came out of their mouths.

Pop off pressure is the same.
Any video that instructs you to pressureise the diaphragm till the needle pops off and the pressure suddenly drops has ZERO knowledge about what they are flapping their gums over.

Click to expand...

Thank you for your very in-depth response.
I appreciate it and I agree with you.
Opening up a carb is not ideal, and that's why I avoid doing it. The gaskets become compromised and etc, but it's frustrating...

I'll order some parts for the the FS85X and report back.

While I have you here, and you're so knowledgeable, I wanted to pick your brain about a few other things.


First of all, why do some small engines idle perfectly "for days", while others can idle for 15-30 seconds and then randomly sputter out and stall?
I assume it's a vacuum leak at some of the intake gaskets, but not sure. I suppose it could be idle set a hair too low and the inertia deficit adds up to eventually stall it. Or maybe the low speed mixture is a tad lean, so it eventually stalls for the same reason.

The reason I ask is I just picked up a Kawasaki single-sided hedge trimmer. The thing is nearly mint condition. It looks to be used once or twice maybe. I mean, really, this things is ridiculously nice. And it's D.O.M. is 2006! So it's obviously been stored away for a long time.

I bought it, knowing it might have some lingering issues from sitting. It starts up easily on choke, idles well, and runs well on non-choke.
But it won't stay running... This thing won't idle, at all. I tried turning up the idle screw to when the blades move, then back off until they stopped moving. This did raise the idle speed, but it still won't stay running.
It runs fine at full throttle.

I also noticed [possibly, not sure] very faint, liquid (possibly oily) starting to form a film around the intake gasket between the carb and cylinder. I believe this is a giveaway that there is a leak at that gasket, but not quite sure.
I've noticed nearly all small engine equipment seems to build up dirt/grime/gunk around the carburetor and fuel system. It's easy to simply assume "that's normal" but there has to be a reason. Thinking a tad deeper, the only logical explanation is moisture is being created, which dirt and dust clings to. It dries up the moisture and cakes up, leaving a film of grime.
Again, thinking deeper, the only logical explanation of the moisture is that there is some oily fuel mix leaking out, but is that normal to some degree?

I've bought/used several new or very new tools, and they all develop that dirty grime on the carb very quickly.

Other minor questions:
Is Kawasaki hand-held equipment 'any good'?
I love Kawasaki engines (as well as their motorcycles!), and know that they have practically built the commercial lawn industry with their legendary FB460V, FC420V and other motors. So I get excited when I see the occasional Kawasaki branded piece of handheld equipment for sale.
"It's gotta be commercial quality!" And I'm a sucker for commercial grade tools.

But it seems their equipment had a short production run, and I have to wonder why. I've also seen the Kawasaki title on random other items (bicycles, electric drill, socket set, and even an electric piano!), so I'm not sure how much if it is the genuine Kawasaki brand vs. slappin' their name on (badge engineering).
I've seen the hedge trimmers, a few string trimmers, a blower or two, and I think that's it.

Mixture adjustment on carbs?
I haven't owned many pieces of Stihl equipment, but on the few pieces I have owned, I've noticed there always seems to be the H/L mixture screws openly available for adjustment.
On both the Kawasaki hedge trimmer, and an Echo HC-152 I own, neither of these carbs have any sort of external adjustment other than idle. The HC-152 and Kawasaki carb almost look to be the same model actually.

Questions questions questions.
If your trimmer will not idle till it runs out of fuel then it is not tuned properly
The cause could be any one of a dozen things from a leaking fuel tank vent to just being set too lean.
At WFO it is easy to maintain running but at lower speeds everything that can cause grief can stop it dead in its tracks.
Right down to a stiff pump diaphragm.
You will have to run through them one at a time

Kawasaki branded engines are top shelf, AFAIK they are contracted out TAS definately made some of the older ones.

The EPA decides if the mixture screws can be accessiable or not so it will depend which particular market the engine was intended to be sold in.

Because of the nature of two strokes breathing, the crank case will usually be slightly above atmospheric pressure when the inlet port opens up so you get a bit of blow back through the carb.
A specific speeds you get reversion happening, google it "Inlet track reversion" a big problem with 4 stroke tuning but also happens with 2 strokes.
Leakage from the crank case seal on the flywheel side will blow oily mist over the engine and of course , the impulse line that works the fuel pump can also vent around the carb.
The last one has been a big problem for the EPA nazis .

bertsmobile1 said:

Questions questions questions.
If your trimmer will not idle till it runs out of fuel then it is not tuned properly
The cause could be any one of a dozen things from a leaking fuel tank vent to just being set too lean.
At WFO it is easy to maintain running but at lower speeds everything that can cause grief can stop it dead in its tracks.
Right down to a stiff pump diaphragm.
You will have to run through them one at a time

Kawasaki branded engines are top shelf, AFAIK they are contracted out TAS definately made some of the older ones.

The EPA decides if the mixture screws can be accessiable or not so it will depend which particular market the engine was intended to be sold in.

Because of the nature of two strokes breathing, the crank case will usually be slightly above atmospheric pressure when the inlet port opens up so you get a bit of blow back through the carb.
A specific speeds you get reversion happening, google it "Inlet track reversion" a big problem with 4 stroke tuning but also happens with 2 strokes.
Leakage from the crank case seal on the flywheel side will blow oily mist over the engine and of course , the impulse line that works the fuel pump can also vent around the carb.
The last one has been a big problem for the EPA nazis .

Click to expand...

About stalling at idle -
I understand it could be any one of many small things. The question then turns into "should I spend the time investigating all of it?"
I love tinkering, but it's cost me many hours at times with no reward other than minor satisfaction or slight learning experiences. Nowadays, I can't afford to lose that time due to work demands. As awful as it can be interpreted, I'd prefer to run the equipment, get work done, and worry about the issues later. Sometimes 'later' turns into never.

I know Kawasaki engines are great. The engines they sell and everyone uses on their mowers. But not so sure about Kawasaki hedge trimmers and such. Not sure if Kawasaki is any good at the small engine business, and they possibly used crap carbs, which is why their OPE line died off quickly. I don't know.

Thanks for your input and experience. I probably won't worry about the minor dirt building up around carb and gas tank. You answered a lot of questions.

Next time you have the carb off, also take a look at the "block" that the carb bolts to, with age, these blocks can crack, and leak air. Which will give you erratic running. Also look closely at the fuel lines, as they can develop cracks, or get real soft and gummy and collapse {suck together}.

Leave it till you have the time to put in.
It is not like the tool will blow up, it is just annoying.

A small leak at the impulse line, the coil air gap being slightly too big, all of these make little difference to the high speed running will make the idle erratic.
It is one of those things that is oft diagnosed by ear.
A plug that is slightly out of size.

Usually you can hear if it is stalling out rich or lean.
The easiest work around is to richen the L to the point that it hangs when you accelerate.

Now it could be just the H & L jets being out of adjustment as mentioned before there are times I have needed to adjust the needles through 4 or more cycles before I get it right.
It just depends where the cross over L to H is.

I have fooled myself on more than one occasion and had a carb running on just the H needle.
With older carbs it is easy because the adjustment is coarse so if going from rich stall to lean stall was more than 3/4 of a turn you knew you had a problem
1) needle or jet damaged
2) running on the other jet

The new EPA compliant ones are harder because the taper is shallower so 2.5 turns of them is 1 turn of the old ones.

Bought some "Chinese" replica, clone carburetor for $15 on Amazon.
Runs great. A tad bit lean on the high end. It would stall if triggered WOT from idle. So I did the "stall lean to stall rich" thing and put it right in the middle, with 1/16 turn to rich side.

Took off shield deflector, extended string out, put bungee cord around throttle, tuned it.

Starts well. Runs perfect. We'll see if it starts acting weird again in a few weeks or after it's been run hard for 30 mins.


Edit: Actually, apparently Stihl is listed as the vendor on the Amazon listing for the carb. $13.91 has me skeptical though. You never know how that stuff works. I've seen it say stuff like

"Genuine Toyota OEM mirror
by Toyota"

Then a few inches over, in another area, it will say "sold by Ghuizo Shenyang"

Bit of a crapp shoot with those carbs of Amazon so cross your fingers.
Check the plug after running for 1/2 hour or so.
If it is white then go a little richer.

bertsmobile1 said:

Bit of a crapp shoot with those carbs of Amazon so cross your fingers.
Check the plug after running for 1/2 hour or so.
If it is white then go a little richer.

Click to expand...

A carburetor is a simple device.
It's 2019.
I trust them to use CAD software to design a part in 2019 that meets 1985 specs.

I understand there are other variables such as quality control, machinery being out of spec, etc, but I'm not going to stress over it.

I can go find a Stihl dealer, ask them for a price, have them give me the highest price they have on the screen, then say "well...Stihl says the MSRP is 1/2 that. Can ya do any better?"
"We can take 10% off, and it will be here in 2 days. We don't stock that one anymore"

I'd rather just order from Amazon, in my home, have it delivered within 48 hours, and have it work 90% as good for 25% of the price.
This is a problem created by Stihl since they insist on the dealer network. Their parts being so far out of reach has caused the knock-off market to run rampant.

Echo and etc is available on Partstree.com, so I buy their genuine parts. No issue.
Stihl is a headache, so I avoid buying their tools in the first place, and have to resort to knock-offs because I don't have time or interest in dicking around with a "Dealer" for a $7 air filter...

I also inspected it quite thoroughly before installing it.

There were obvious differences between the knock-off and genuine Stihl carb, for sure. Such as the part line made from the casting mold. The metal quality looks subpar to the original. It was not de-burred as well, but still more than satisfactory.
The mating surface, although not cosmetically perfect, seals fine, which is all that matters.
The 'velocity stack' of the inlet opening was smooth enough for my taste.

It's a dang good replica that would be indistinguishable from the original in the eyes of 95% of the population. It's also indistinguishable in performance as far as I can tell. And I got a pretty dang good feel for this stuff after 9 years of tinkering on cars, small engine equipment, engineering school, etc. I can hear a sputtering idle, struggling to make power, bogging, popping, bearing noises, etc where other people, even after repeatedly trying to point it out, can't hear anything. Not trying to brag, it's just something that comes with years of running engines. I suppose similar to how I'm musically retarded. People say "can't you just determine the notes of a song by ear?" and I just can't. Not if my life depended on it.

In addition, the adjustment screws are MUCH better. Simple flathead type screws vs the stupid Stihl screws that break immediately. I understand that may be EPA influenced, but still frustrating as far as it concerns my user-experience.

It's quite impressive actually. You can literally slap it on and go. A 5 minute swap out. This is not typically the case in other areas, such as replica car parts. Those usually have fitment issues, need to be 'tweaked', don't fit at all, etc. I've run into that so many times.
I don't think very highly of "genuine Stihl" carburetors (more accurately, Zama, I suppose) at this point anyway. Every single Stihl tool I've owned (all used, I admit) has hard carb issues, as well as about 75% of them for sale on craigslist.
It's a concerning issue when the knock-off carburetor market is so strong due to the demand...


One thing I am concerned about though is the seemingly universal-ity of these carbs.
I purchased the carb for this trimmer, a FS85 RX. It's got the 25cc motor. Okay fine. That carb is tuned for a 25cc motor. And Stihl puts their 25cc motor in multiple different tools. Fine.
But these carbs for sale say they fit like 40 different tools. Which is a bit...curious, in my opinion.
There is undoubtedly very specific tuning differences that Stihl made between various tools. Such as a lightweight string trimmer that's supposed to scream, vs. a pole saw that needs power down low, maybe.

I also bought a carb for my FC95 edger, which is a heavy-duty commercial tool with decent power. The listing said it also fit FS45 trimmers, which is a silly, low-end curved shaft homeowner trimmer.
So...eh

TerraForte said:

A carburetor is a simple device.
It's 2019.
I trust them to use CAD software to design a part in 2019 that meets 1985 specs.

I understand there are other variables such as quality control, machinery being out of spec, etc, but I'm not going to stress over it.

I can go find a Stihl dealer, ask them for a price, have them give me the highest price they have on the screen, then say "well...Stihl says the MSRP is 1/2 that. Can ya do any better?"
"We can take 10% off, and it will be here in 2 days. We don't stock that one anymore"

I'd rather just order from Amazon, in my home, have it delivered within 48 hours, and have it work 90% as good for 25% of the price.
This is a problem created by Stihl since they insist on the dealer network. Their parts being so far out of reach has caused the knock-off market to run rampant.

Echo and etc is available on Partstree.com, so I buy their genuine parts. No issue.
Stihl is a headache, so I avoid buying their tools in the first place, and have to resort to knock-offs because I don't have time or interest in dicking around with a "Dealer" for a $7 air filter...

Click to expand...

It is a simple priceing thing.
I charge out $ 60/hr.
hand helds have a flat $ 45 fee for a service or $ 60 for a repair ( + parts )
I can spend 20 hours trying to clean a blocked carb or $ 20 on a new one.
Thus it is a no brainer, fit a KNOW GOOD QUALITY aftermarket carb, toss the bad one in the some day box.
Every now & then I have a carb day and might clean & rebuild 10 to 30 carbs, wrap them up & pop them on the shelf for latter.
The trick is getting a good one.
There is no such thing as process scrap in China.
Every thing that comes off the end of the line gets sold, working or not.
The beast ones end up in the warehouses of after market parts wholesalers & flogged to people like me, unaffiliated repair workshops.
What is left over ends up being sold annonomously on the web where if it does not work, tough luck.
A 12 year old can build a "web shop" that looks like it is a sound company where in reality it is nothing more than a computer in some ones garage and that person is nothing more than a trader.They buy what is cheap when it is available & sell it at the highest price they can get for it, They have less than no idea of what they are selling , it is just stuff to them.
We used to rent out empty pallet space at the last warehouse that I ran on a week by week basis.
Very good for us as we could run on 100% fill rate so the cost per item despatch was as low as we could get it.
The goods would arrive , oft in a container full of all sorts of things like condoms, fake medications , maternity bras, truck part, mower parts , plants , vases , your name it.
They sent us the picking slip & despatch details & we did our bit.
Nothing odd to see the same part from the same pallet being invoiced out at different prices with different suppliers names on the invoice .
All of it sold via the web and lot via Amazon Aust or via late night TV promotion.
When the products stopped moving or we got down to the last layer or two the instructions were usually to toss the remainder in the garbage skip so they could put another full pallet in its place of faster moving goods.
Now some of this stuff was good, some had packaging that would make it illegal to sell in a real retail shop but at least 1/4 was defective trash.

In defence of Stihl & all the other original equipment companies, it costs more to store, pick & despatch most products than it does to make them, particularly if it is a carburettor for a 20 year old trimer.
A pallet space in my warehouse was about $ 5 / week and the pallet was another $ 2 /week.
Unless it was picked daily then it went progressively higher than the lower 2 rows so that means a fork pick which adds another $ 6.25 then it has to be packed, invoiced despatched to the dealer then finally billed & sold to you.
Unless people have worked in warehousing & logistics very few have any idea about just how much this adds to the price of a product.
The ignorant are usually the loudest proclaimers of just how much they are being ripped off when in reality the part is being sold to them at a massive loss.
Conspiracly & profiteering is a lot easier to sell to joe public than the cold facts.
We once worked out that a bottle of wine from a single box sitting on a pallet for an entire year would cost $ 67 by the time it got to the retailer in warehousing & logistics alone.

One of the reason why Chinese copy engines are so cheap is there are none of these costs added to them.
They go direct from the factory to the end user, which is efficient , just so long as you never have to supply parts for them.
I can get identical engines from Loncin, Zenshing, Ducar & Liffan and by identical I mean every part will interchange between them.
The Loncin is now 20% more expensive than the Ducar for no reason other than they now have a distribution network which adds substantially to their fixed costs.
The Ducar have a local agent who only stocks complete engines, if you want parts then "Honda parts will fit"
Zenshing & Liffan are the cheapest, I order them through a local agent & they arrive in the shipping container that they left the factory in.
The driver tosses mine off the back then goes to the next customer so their net distribution costs is one truck & driver for how ever long it takes him to empty the container.
If I am not here for the 2 day delivery window so miss delivery there is a $ 100 redelivery fee.
Again if you want parts the "Honda parts will fit".
They all do this because they know that adding a local distribution network will nearly double the wholesale cost of the engine, and price is their only selling point.

Never got an email notification for this one, so I just saw it now.

You may be right. Sounds pretty convincing. I don't have the experience with warehousing and logistics that you do, so I can't comment on that.

All I can say is 2 things regarding my experience with my Stihl tool(s) so far,

1. I stopped in a local mower repair shop that is a Stihl dealer. I asked for a simple maintenance kit for my FS85x. Air filter, fuel filter, spark plug. $20. Oooookay...I'll pay it and won't even argue. I looked at the fuel filter and it was brand-less! I was considering ordering the same maint kit for my 5 other Stihl tools but decided dropping $100 on a couple of air filters and spark plugs is pretty ridiculous. Then I ask about a clutch spring for my FC96. "That'll be about $10". I didn't say anything, but I had already ordered it from a different dealer for $4.16....I was also looking at the other stuff in stock, of course not a single item has a price tag on it, so I have to ask for every little thing from a $500 trimmer to a $4 bottle of oil. I looked at a FS91R "Oh! We have overstock on those, we'll give you a discount! We'll drop the price from $359 to $329 and do $319 if you buy more than 1!" When I went to the other dealer (3 miles away) to pick up the clutch spring, they had FS91Rs hanging (with price tags) for $329 each :laughing:
2. The carb has been working great so far. I've checked the spark plug a couple of times. I also bought a new carb for my Echo PAS-266 unit. Made in 2015 and great so far. The throttle cable was very loose, and the threads for the adjustment nut were stripped. Also occasionally stalls at idle after 30-45 seconds, and hesitates just a hair at WOT from idle. I looked into the price of new I/M gaskets and the 'rotor' piece that has the throttle cable adjustment nut threads. Rotor ~$25, and gaskets $7. Plus shipping. I just bought a whole new carb kit for $13 and it's been working great.

Last night I just picked up a lot of 5 Stihl BR600s that were "for parts or repair" from one of these big lawn companies. I just assumed the guy was the type to trash anything that was 'old' and just buy new every 3-4 years. I assumed they had gummed up carbs or maybe needed a valve adjustment or spark arrester screen cleaned.
Well I got home and pulled on one just for fun. It pulled like the spark plug was removed. Just about zero resistance on the pull cord. Odd...Is the fan moving when I pull it? Yes...
Then I checked the other 4 and they all have significantly decreased resistance when pulling.
Oh no...
Not sure if a push rod broke leaving a valve wide open or what

I have about a dozen of them here , all from one customer.
After about 3 or so years the bores are cactus.
All of them are ovaled.
The new replacement BR 700 or 750, can't remember runs 300 rpm slower.
OTOH he is still using the BR400's
What you have to remember is back pack blowers get used a lot of hours.
No one bothers to strap on on to blow a few clippings off a driveway.
This particular customer has a lot of large car parks that get blown down every day.

And yes some dealers are cheaper than others.
Down here one Stihl dealer is a stand alone outfit in an industrial estate & pays $ 2500.week rent
I get mine form a dealer who is multi brands and in on a block his family has owned for 3 generations, he gives me parts for cost +10%.
Some dealers just do not want to bother selling parts to the public because it costs them money to make the small sales.
These are usually run by accountants .
Raising & printing an invoice costs around $ 2.00 and then there is the time that the sales assistant takes to take your order, find the parts bag then print the invoice & give them all to you.
This all costs money and then there is the lost profits on your parts inventory.
I have an inventory which is about 3 times my annual turnover because as an independent it can take many weeks to get some parts ( Stihl are worse ).
Right now I am buying my Briggs parts from the USA & paying shipping to,Australia because it is taking Briggs Aust on average a month and Jacks or Parts Direct will have them here in 10 to 14 days.
So this cost me a lot of profits that I could have eaten and will not make me a brass razoo extra profit ( except the stuff I get direct from China ) and may dealers are in the same boot, only I am not paying a monetary rent, or wages.
Now if I was to factor the true price of ordering in the stock, freight, sorting them storing them then invoicing the customer I doubt I would actually be making a profit on anything that was less than $ 20 ( $ 5.00 of profit ).
So some one with an MBA will decide that all parts would have a minimum price of $ 20 each because they do not understand the value of traffic coming through the shop and can not understand what a loss leader is.

Interesting input, especially on the BR600 cylinders going bad.

I've been a busy guy lately. Bought that lot of 5 BR600s and managed to get all of them running. Only 1 required any replacement parts.
Out of the 5, 3 of them were 10-14 years old, and the other 2 were from 2012 and 2015.

The 2015 was the newest and nicest looking one, so that's the one I tried first. It had no resistance when pulling, so I looked deeper. Tore the whole machine down and found the cam gear (plastic) had exploded. Took out a cam follower with it. Yikes.

I priced out the parts for that one from my less-than-competent local dealer... $56 for cam gear, 2 push rods, 2 followers, and cork valve cover gasket. Ugh, fine. I'll just write it down as an "investment in my education". A learning experience, right?

While waiting for the parts to come in, I looked at the other blowers. I developed a system of going through them. First was to check valve clearances, of which they were all significantly out of spec. This step alone got one of the blowers running tip-top.
Second order was to check for spark. One had a clipped off wire lead, and the other had a coil that gave no spark. Used a jumper wire on the cut-off coil, and that blower fired up. So the coil was good, but cosmetically bad.
I swapped around a coil and got the 3rd one fired up.

After the valves and spark checked out, I was stumped for a minute or two. Cranked it several times, feeding it ether. Won't fire. Hmmm...
A-ha! Spark arrestor screen is completely clogged!
Removed the mesh and it fired right up.

Then got the replacement cam gear parts in and installed those. What a mess. The plastic bits get chewed up into various granularity and can turn into paste with the help of the fuel mix. I spent a considerable amount of time properly cleaning out the crankcase.
Installed parts, set valve timing, and away she purred.

I actually went back and got the "bad" coil to work after brushing off the contacts. So, didn't even have to fiddle with a crap ebay knock-off ignition coil!

Although they all ran, and were complete, they weren't all perfect. As you would expect from 12 year old blower that's been used commercially. Ripped straps, gouged plastics, dirty, missing a few screws here and there, wrong fasteners jammed into threads, etc.
But, they all ran, and the 'bones' were solid. They all idled perfectly, and wound up through the RPM range as they should. No knocking, no tapping, no smoking, etc. All of them would have made perfectly fine back-up machines, or even a main unit for a fly-by-night operation.

Super simple little machines, and quite robust aside from the cam timing system. But I guess the defence with that one is that it's reliable when valve adjustments are done properly. Not sure, I haven't put 100s or 1000s of hours on a Stihl 4-MIX machine.
All I know is, going forward, I would definitely jump on another "for parts or repair" BR600 if it was complete and not run over with a truck (which they all seem to look like...).

I think you are right about the BR700 - although I'm not sure it's intentional that it runs at 300rpm less. I don't even know that it does, but it's possible.

When I got these BR600s, I didn't actually know all that much about them. My dad gave me a BR550 a few years back that I used for about 1 season until it ran poorly. I just used it to blow grass clippings off of the 15ft of sidewalk kinda stuff. I took it apart, didn't really know what I was doing, and it sat in my garage.
So I learned a lot with these BR600s, specifically what the heck the difference between the BR500, 550s, 600s, and 700s is.
Funny enough it's all the same 65cc motor.
The BR500 is the "quiet one". Same price as BR600. They actually de-tune the motor and use a different blower vane to create lower air speeds, I believe. Then they put a damper (expansion tube) on the output pipe.
The BR550 is just a marketing ploy. It's about 97% identical to the BR600 - same carb, same power output, etc. Except they use a different fan that creates more air speed, but less air volume. Even though the 550 parts cost more, the blower was sold for ~$30 less.
The 600 is the benchmark comparison.
And the 700 is the newest one. Another marketing ploy where Stihl adds on $50 to again lower the air speed to raise the air volume. So they just use a slightly different blower vane on the exact same machine.

Well done.
Learning is always worthwhile regardless of the price.
You will also find that the engine speeds increase as you go up the scale.
Depending upon what you are shifting volume & speed interchange .
High speed low volume is best for simple blowing clippings off drives
High volume low speed for moving mulch around.

Now consider the time it took you to make the repairs divide it by 2 or 3 to allow for lack of experience then multiply it by the $ 50 labour fee the service centre charges.
Then factor in the cost of a crew member sitting on their butts doing nothing because the blower dosen't blow, remember the shop will if you are lucky give you 3 months warranty on the repair.
Then there is the attitude of the crew members.
The company wants them to do a top quality job yet keeps on getting this worn out blower fixed which is always breaking down & making things difficult for them.
So it is not worthwhile for most crews to spend money on repairs for small items.

All the better for you.
I supply my commercial customers with a loaner for all small tools that I repair.
In many cases it is an old worn out one they gave to me for spares that I managed to get working again.
The rule of thumb is less that 1/3 the replacement price then fix it otherwise trash it, it is just not worth their while.
The BR's come in twice a year for service & I charge $ 120 to do it.
If I factored the time I spent cleaning them before I start to work on them, I would be doing them at a loss.
That price is for a full service which includes setting those !#!#!#!# valve lashes and fitting a new rocker cover gasket.
Also a new fuel filter unit complete with tank grommet and new Tygon fuel lines.

This ends up costing the company more than run them till they break & replace but the crews work unsupervised and travel a long way from the depot so a break down costs a lot more than the repair costs.
Ideally they would carry a back up for everything but there is only so much space in a truck & trailer.

somewhat of an update in my quasi-"Stihl blower refurb side-hustle"

I picked up another lot of 5 blowers. This time 2 Echo PB-770s, 2 PB-755s, and 1 Stihl. I thought it was a BR600, but it turned out to be a BR700.
90% identical machine, but some interesting differences. The main thing that Stihl has done (throughout the BR range from the BR500 all the way to the BR700) is trade air speed for air volume. All the machines use the same motor (although the BR500 is choked and yields roughly 60% power compared to the rest), and same fundamentals. Stihl just tweaks the blower vane to shift on the speed vs. volume curve.
The BR700 boasts the most air volume.
Upon further inspection and disassembly, the fan housing is slightly different, and has flat-ish sides rather than a fully round shape. The blower vane also specifically says "for BR700 only" on it.
As can be easily seen via stock photos, the tube assembly is also modified with its large orange spin-nut that allows the tube length to be changed tool-less-ly, as well as the position of the throttle handle.

Other than that, the blower was 99% identical.


Anyway, I picked it up as a non-runner and assumed the worst - shattered timing gear - despite the BR700s being newer machines overall. This one had a D.O.M. of 10/2016 so I was slightly optimistic.
Popped off the valve cover and the valves did not move. Yep, as expected. So I ordered the cam gear, push rods, cam followers, valve cover gasket, and some new red [overpriced] red gasket sealant for good measure.
I did the dirty work of cleaning out the cylinder assembly of the bits of rubble and debris from the cam wheel...or so I thought.

What was interesting is that, upon removing the timing cover, the cam wheel looked perfectly intact. So I spun the flywheel side and the cam wheel did not move. I quickly found out this was because only the very bottom portion of the cam wheel was broken and it was concealed by the housing.
I go to clean out the bottom end, and the crank just pops out unexpectedly. Odd, I thought, as I could have sworn the BR600 I last worked on had some bearing caps that held it in tightly, as I did try somewhat firmly to remove it.

Well, that's cool. Now I have better access to clean everything out.
After about 40 minutes of cleaning everything out, I notice something overwhelmingly obvious staring me right in the face.

I had one of those *blink blink* moments. "Is that...supposed to be like that? No way"
Then I quickly assess that, no, it most definitely is not supposed to be like that.

So my understanding of the method of failure of this machine instantly changed. I had thought an overdue valve adjustment created a large valve lash scenario, which caused the push rod to sharply impact the cam wheel upon a sudden throttle blip, stressing it and eventually causing it to shatter. This now seems not to be the case... It very much seems that something causes the piston skirt to stress, then fatigue and fracture. Then it seems like a bit of debris gets lodged in the cam wheel teeth, and that's what causes it to shatter.
I cannot, for the life of me, figure out what causes the skirt to come apart like that though.

I had already purchased the cam timing parts, so I decided to go ahead an order a new piston/rings/wrist pin kit for $30 from a vendor I found on Amazon.
The cylinder didn't look pristine by any means, but did look similar to "good used" jugs for sale on ebay so :confused3:

Installed piston, re-assembled, and it worked. Started up immediately, and blew air. With my mild experience with the BR600s, it seemed to not wind up as much, but that could also be what you mentioned in terms of them capping the RPMs on the 700s. It didn't seem as loud, but, again, unsure if that is due to a loss of power from a shot cylinder, or simply a re-design. It seemed to blow as much as other backpack blowers, but that's not a very scientific assessment.
One odd thing is that it did a bit of a 'hang' when letting off the throttle. It would be at full throttle, then [release throttle] and it would settle at ~15% throttle for 1-2 seconds, then fall down to idle speed.
Tinkered with the H/L jets and couldn't iron that one out, so I thought maybe it was a bit of the compression charge leaking through the rings and artificially feeding it fuel, but my understanding of 2-strokes is pretty shallow in that respect.

Also, I had another question for you:


What's the deal with compression testing a 2-stroke?
I can't seem to get a reading that makes sense.

I tried to test a potentially ruined cylinder on a Dolmar trimmer.
I used a compression tester and it only rang up to 25psi. I couldn't believe it. I thought it wasn't threaded in enough for the O-ring to seal or some other issue. So I tested it on a very new Stihl FC96 in nearly mint condition. It barely said ~26-27 psi. Then I bought a new compression tester and the results came out the same. I pulled the starter several times, throttle open/closed, choke on/off, and all combinations. Not sure if I'm doing something wrong or if the tools aren't compatible. I tried to check very closely for air leaks but couldn't find anything.

Because of the very low volume of the combustion chamber it is hard to get good secondary pressure readings.
Unlike a 4 stroke, you need to have both primary & secondary compression.
If the crankcase seals are shot then you can not get primary pressure in which case your secondary will be low.

I never bother with secondary compression testing.
I do primary testing then leak down testing for the rings.

Apart from that most car testers expect to be seeing 200 cc or more per stroke so when you only have 25 cc they struggle so you might need to give the 50 to 100 pulls till the pressiure gauge stops moving.
This is the reason why I swapped to leak down, so much easier to do.
There are compression testers specifically designed for low volume engines but the price is a touch more than I can justify.

Back to your broken piston.
the piston pins on these are a tight fit as they run on a needle roller little end.
being a needle roller it takes 5/8 of SFA to jamb the rollers
That rod looks a little cooked to me what does the underside of the piston look like ?
If there is burned oil in there then it has been overheating probably due to a loose carb.
When you looked at these did you not notice that they all use different carbs ?
The pump & metering diaphragm are the same but the main jet & needle are different.

If unsure go to the Walbro parts pages and check the parts numbers.
If they are different then the part is different,
When it come to Cube carbs the differences can be the size of fairy wings which is why the diaphragms & gaskets are all cut slightly different shapes because you will need a metrology lab to measure the actual differences.

Got another stumper

Got carried away and got a Poulan chainsaw in a package deal. A "Woodsmaster 2250, 2.2CID"
Older model, seems slightly more solid than newer Poulan stuff

36cc motor, Walbro carb originally.
Got it as a jumble of parts, but everything present. Put it back together and it surprisingly fired right up.
At that point, it would rev, but would not idle. I could start it at full throttle and seemed to run indefinitely but would die upon coming down.
One of the vibration-damper springs was also broken.

Not something anyone wants to buy in this condition, but also not worth scrapping since the saw looked cosmetically nearly brand new.
So I figured I'd buy a spring kit and a clone-carb for $20 total.

Springs were quite nice actually.

Saw idled perfectly! But then died under load.
I must have spent an hour trying to tune that stupid thing but I couldn't get it right. I would turn them both all the way in, then CCW the Low ~1/2 turn until it idled perfectly, then CCW the H extremely slowly. I couldn't seem to get results that made any sense when enriching the H. I'm prepared for the "junk clone carb is junk" reply.

It will either idle perfectly and die under load, or only start under full throttle, run perfectly, then die when coming to idle.

I would get the low speed circuit tuned in perfectly, then go for the high. I would adjust the high a bit, and then it wouldn't idle! And wouldn't re-start until re-tuning the low. Then it wouldn't rev!
It was this never ending loop of either low or high speed working, but never both.

What gives?


When does the low speed circuit taper off? How much overlap between H/L circuits on these small carbs? I'm familiar with the multiple curves on a CV carb on a motorcycle, for example, always 2 or 3 jets in contribution, but I'm sure these small carbs aren't as 'smooth'.

Just to be different.
Please start a new thread with your new problem
1) it avoids confusion
2) it stops people reading 2 pages of stuff that has no relevance to your current problem.
See you there

bertsmobile1 said:

Leave it till you have the time to put in.
It is not like the tool will blow up, it is just annoying.

A small leak at the impulse line, the coil air gap being slightly too big, all of these make little difference to the high speed running will make the idle erratic.
It is one of those things that is oft diagnosed by ear.
A plug that is slightly out of size.

Usually you can hear if it is stalling out rich or lean.
The easiest work around is to richen the L to the point that it hangs when you accelerate.

Now it could be just the H & L jets being out of adjustment as mentioned before there are times I have needed to adjust the needles through 4 or more cycles before I get it right.
It just depends where the cross over L to H is.

I have fooled myself on more than one occasion and had a carb running on just the H needle.
With older carbs it is easy because the adjustment is coarse so if going from rich stall to lean stall was more than 3/4 of a turn you knew you had a problem
1) needle or jet damaged
2) running on the other jet

The new EPA compliant ones are harder because the taper is shallower so 2.5 turns of them is 1 turn of the old ones.

Click to expand...

You must have a hell of a set of ears. Being able to tell if a 2 cycle dies because it's too rich or lean, baffles me. When one dies, I just hear it die.

LOL... I have tinnitus, so buzzing is what I hear mostly.

PTmowerMech said:

You must have a hell of a set of ears. Being able to tell if a 2 cycle dies because it's too rich or lean, baffles me. When one dies, I just hear it die.

LOL... I have tinnitus, so buzzing is what I hear mostly.

Click to expand...

So do I and most mechanics that I know
Next time your are tuning the H needle , take it a little too far in both directions till the engine actually stops.
Too rich will 8 stroke, miss a bit then just peter out with the odd bang or two before it stops
The exhaust becomes deeper in sound and sort of fluffy
Too lean will just keep on getting faster then nothing
The exhaust note will become higher and sharper like a blue smoke with a resonant exhaust pipe.
Two totally different sounds

bertsmobile1 said:

So do I and most mechanics that I know
Next time your are tuning the H needle , take it a little too far in both directions till the engine actually stops.
Too rich will 8 stroke, miss a bit then just peter out with the odd bang or two before it stops
The exhaust becomes deeper in sound and sort of fluffy
Too lean will just keep on getting faster then nothing
The exhaust note will become higher and sharper like a blue smoke with a resonant exhaust pipe.
Two totally different sounds

Click to expand...

Very good explanation. Thank you.

This forum seriously needs a thank you button.

PTmowerMech said:

Very good explanation. Thank you.

This forum seriously needs a thank you button.

Click to expand...

Yes, a thank you button would be good. Some posts are so informative and thorough, and deserve recognition of the time and effort taken to freely help others.

While I'm here.. Thank you!

HotnDusty said:

Yes, a thank you button would be good. Some posts are so informative and thorough, and deserve recognition of the time and effort taken to freely help others.

While I'm here.. Thank you!

Click to expand...

Not a big fan of LIKE , THANKS etc etc.
Always better to do it as a post.
It very quickly leads to ego problems and people seeking gratification from getting the most likes.
It also tends to prevent people being blunt and oft a blunt answer is exactly what is required to get the OP to see reality.
Many seem to think this is rude, but wrong is wrong no matter how you dress it.
However the very best "thank you" is a "got it fixed and it is working great" post.
Then others who read the thread will realize that the fix worked.

I would be a big fan of cash,
or better, a Paypal button....

bertsmobile1 said:

Not a big fan of LIKE , THANKS etc etc.
Always better to do it as a post.
It very quickly leads to ego problems and people seeking gratification from getting the most likes.
It also tends to prevent people being blunt and oft a blunt answer is exactly what is required to get the OP to see reality.
Many seem to think this is rude, but wrong is wrong no matter how you dress it.
However the very best "thank you" is a "got it fixed and it is working great" post.
Then others who read the thread will realize that the fix worked.

Click to expand...

LOL... You'd spend a lot of your time looking at all the liked posts you made. he he he he he.