FS85X just does not want to tune in properly

TerraForte

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TL:DR;
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.
20190705_100433.jpg
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.
20190705_100439.jpg
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.
20190705_100447.jpg
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.
 

bertsmobile1

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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.
 

TerraForte

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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.

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.
 

bertsmobile1

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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 .
 

TerraForte

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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 .

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.
 

Fish

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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}.
 

bertsmobile1

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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.
 

TerraForte

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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"
 

bertsmobile1

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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.
 

TerraForte

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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.

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...
 
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