FS 55 not priming

bertsmobile1 said:

No they are not plastic.
The diaphragm that make the fuel pump work are plastic.
All gaskets are fiber board of some sort and should be considered as a single use item.
Sealing these cube carbs air tight is quite difficult and reusing the carbs is a sure fire way to inorduce a leak.

Click to expand...

So, don't reuse gaskets. Thanks!

bertsmobile1 said:

Well it all depends if you want to repair it or destroy it.
If the lattr, the do it properly with a 1/4" bead of silicon on everything.

If that does not work the wrap the whole thing in duct tape and give it a liberal spray with WD 40.

Now I have your attention and just before you send me an abusive flame, how about some better description of what your problem is.

Won't prime means what ?
Primer bulb will not fill with fuel ?
trimmer will not start ?

Did you really buy a new carb, the pull the new carb apart & refit the gaskets oiled ?
If so what on earth made you do this ?
If the new carb did not prime then you take it back for a refund, or try to find the EXTERNAL REASON why it is not working ?

Did you suck on the fuel delivery line to ensure fuel was flowing through it ?

Did you pressurise the tank to test he integrity of the tank & fuel lines ?
do you have the basic tool needed to work on cube carbs, including a vaccuum / pressure tester.
Did you do the work in a very clean room on a clean table covered with clean paprer ?

Click to expand...

Thanks for the reply. I'll reply in order.

If I use the Permatex, I'd use a thin layer. Less than 1/32". A lot less. Putting some duct tape on it *might* give me the opportunity to explain how the local STIHL dealer screwed me out of $70 way back when. Don't see where WD 40 would help in this situation. Although I do use it at times.

Life is too short for flaming.

Originally, the primer bulb would compress and stay that way for a while. The trimmer would not start. The trimmer did/does start with a spray of starting fluid. Runs well until the starting fluid is exhausted. Not good long term solution.

I disassembled and cleaned the old carb. This did make the primer bulb work a bit better, some fuel was being drawn into it. Still wouldn't start without starting fluid. I then bought a replacement carb and installed it using the old gaskets dry. Same result. I still have the new carb.

No, I didn't suck on the fuel lines. Don't see it as a good idea. If it's blocked I don't want whatever it is inside of *me*. Blowing on the line is an idea. I suspect that the original fuel line is, at least, part of the problem. Reusing the old gaskets might also be involved. No signs of fuel leaking from the tank.

I don't have the test tools, etc. I *did* shop around and came to the conclusion that quality tools would cost more than a new trimmer.

My plan is to:
- Build a new fuel line assembly. I'll be down at NAPA next week. Probably use Tygon fuel tubing and a new grommet. Not sure about using the Permatex sealant on this. Might end up using Seal All where the tubes meet the grommet. NAPA has Tygon, the grommet may be an online purchase.
- Install new gaskets, the replacement carb came with them. Probably use sealant here.
- Use a Dremel to make it easier to get to the spark plug.
- See if it starts.

Excellent,
A man with a sence of humour and good outlook on life sorry I left out the smileys.
Sealants on the manifold gaskets are ok if used very sparingly as the small hole for the impulse that works the fuel pump is easily bocked.
Sealants must never be used on the internal carb gaskets which is what I thought you were talking about. They must go in dry.
Manifold gaskets are always replaced as they do compress and are under $ 1.00 wholesale so it is a cheap way to eliminate one set of possible problems.

As you have installed a new carb with little improvement we can fairly safely assume the problem is in the fuel tank.
So a new fuel filter is a good plan and if you are going to do that then replace the fuel lines as well.
Tygon is the best available fuel line at the moment so that is a good call.
Also check the return line becuse if it is blocked you can't suck fuel.
However as the primer goes down that suggest the return is passing air.
And a touch of silicon lube works wonders.

To fit the new fuel line, cut the end with a slash , fit a drill bit up the tube ( blunt end of course ) to give you something to push on.
Feed the tube through then pull it out the fller neck square off the end and fit the filter.
The more expensive porcelean filters ar better then the felt ones and it makes no difference to the engine but the felt ones loose fibers that block off the internal filters in the carb causing the problems you are having.
Stihl sell complete fuel line assemblies ready to fit that naturally cost a lot more but are far easier to fit.

bertsmobile1 said:

Excellent,
A man with a sence of humour and good outlook on life sorry I left out the smileys.
Sealants on the manifold gaskets are ok if used very sparingly as the small hole for the impulse that works the fuel pump is easily bocked.
Sealants must never be used on the internal carb gaskets which is what I thought you were talking about. They must go in dry.
Manifold gaskets are always replaced as they do compress and are under $ 1.00 wholesale so it is a cheap way to eliminate one set of possible problems.

As you have installed a new carb with little improvement we can fairly safely assume the problem is in the fuel tank.
So a new fuel filter is a good plan and if you are going to do that then replace the fuel lines as well.
Tygon is the best available fuel line at the moment so that is a good call.
Also check the return line becuse if it is blocked you can't suck fuel.
However as the primer goes down that suggest the return is passing air.
And a touch of silicon lube works wonders.

To fit the new fuel line, cut the end with a slash , fit a drill bit up the tube ( blunt end of course ) to give you something to push on.
Feed the tube through then pull it out the fller neck square off the end and fit the filter.
The more expensive porcelean filters ar better then the felt ones and it makes no difference to the engine but the felt ones loose fibers that block off the internal filters in the carb causing the problems you are having.
Stihl sell complete fuel line assemblies ready to fit that naturally cost a lot more but are far easier to fit.

Click to expand...

I'll replace the gaskets. Already have them. Need to make sure to install them correctly. One fits between engine and carb, the other between carb and choke. The gaskets are different. Shape, hole pattern.

Finding out that NAPA sells Tygon was great. They want about $1.50/foot. Same price as online without paying for shipping. I'll probably get three feet of 3/16" x 1/8" and three feet of 3/16" x 3/32". Far more than I need, long shelf life. Also have a Mantis(Echo) trimmer to fix. Fixing the Mantis should be a lot easier after figuring out the trimmer.

The fuel filter that I have is fine. I blew through it. Yum. Could hear the airflow.

I decided to make a fuel line assembly rather than buying one for these reasons:
- I'm not going to let the Local Stihl dealer screw me again.
- Getting this part online is very difficult. Apparently Stihl doesn't like the internet in the US. The places that I could find to buy were either ePray related, wanted an arm and a leg for shipping, or both.
- I wanted to do it right.

If you're interested the hole in the gas tank is about 19mm diameter.

Never heard of a porcelain gasket.

Thanks!

There is a tiny hole . about 1 to 2 mm in the gasket that goes between the engine & the carb.
It lines up with a similar hole in the engine side of the carb.
This allows pressure pulses from the crankcase to work the fuel pump.
If it is blocked or leaking the engine will start after priming but will not run.

OTOH some Stihl engines have a seperate impulse line. usually a convoluted tube that does the same thing.
I did not check which one yours was before I wrote the response.
If you have one of these that tube should be replaced as well.
You use the heavy walled Tygon for that.
Check what line you buy.
Inlet tube is double wall thickness to prevent it collapsing so check both the internal & external diameters.
I use drill bits for measuring the internal diameters.

bertsmobile1 said:

There is a tiny hole . about 1 to 2 mm in the gasket that goes between the engine & the carb.
It lines up with a similar hole in the engine side of the carb.
This allows pressure pulses from the crankcase to work the fuel pump.
If it is blocked or leaking the engine will start after priming but will not run.

OTOH some Stihl engines have a seperate impulse line. usually a convoluted tube that does the same thing.
I did not check which one yours was before I wrote the response.
If you have one of these that tube should be replaced as well.
You use the heavy walled Tygon for that.
Check what line you buy.
Inlet tube is double wall thickness to prevent it collapsing so check both the internal & external diameters.
I use drill bits for measuring the internal diameters.

Click to expand...

Sounds like the small hole above, or below, the Venturi tube. I'll look when installing. The OEM fuel attachment is two hose. One hose, attached to the fuel filter, goes to the bottom nipple on the carb. The other goes to the top nipple.

It will be a few weeks, or more, until I have everything. Shipping from China on the grommets...

Thanks!

Bad move with the Chineese grommets.
A lot of them are made with very high latex content in the rubber which is neither UV resistant nor fuel resistant.
So cross your fingers with that one.
Yes the small hole over or above the venturi hole is the impulse line.

Without any gear, try to get the fuel line to syphon the contents of the fuel tank.
Blowing through it is not a real good test.
You can blow through a water contaminated filter but it will not flow fuel.

bertsmobile1 said:

Bad move with the Chineese grommets.
A lot of them are made with very high latex content in the rubber which is neither UV resistant nor fuel resistant.
So cross your fingers with that one.
Yes the small hole over or above the venturi hole is the impulse line.

Without any gear, try to get the fuel line to syphon the contents of the fuel tank.
Blowing through it is not a real good test.
You can blow through a water contaminated filter but it will not flow fuel.

Click to expand...

Maybe that's why there are three grommets in the package. I wonder whether coating the grommet lightly with the Permatex sealer would help. Cheap insurance?

I tried the trimmer without a filter with the same result. The filter was saturated with gas when I took it off. Multiple simultaneous issues are possible. The filter does look very clean. Something to ponder.

Thanks!

I got everything I thought I would need and put it together. Still no joy but it is promising.

Putting together the fuel line assembly was easy. The only mistake I made was to cut the lines a little too long. Caused kinking. Easy to fix.

The trimmer still doesn't want to start without starting fluid. Not for long anyway. Without the starting fluid it will 'cough' but not start idling. Fortunately(?) there is a small air bubble in the fuel line, makes it easier to see when fuel moves.

When I use the priming bulb I can see fuel move and bubbles in the tank. Can see several air bubbles moving from the carb to the fuel tank. This tells me that fuel is moving through the lines and the fuel filter.

I checked the small hole(impulse?). It doesn't seem to be blocked.

One thing I noticed is that the idle is/was *way* too fast on starting fluid. This led me to believe that the factory didn't even try to tune the high/low screws. Closing them required several turns. Maybe didn't try to do the idle screw either. I closed (clockwise) both the high and low and backed them out two turns. At this point the trimmer would cough a few times. Too rich?

I need to get the trimmer running, even poorly, to do any real adjusting.

Back at it tomorrow!

According to Manuel the Mexican Mechanic the two needles are set to 3 turns out each so give them another turn and try again.

Also try starting with the trigger pulled in and the idle wound up full
Adjust the high speed jet first, lean ( in ) till it starts to faulter then rich ( out) till it starts to faulter then slightly to the rich side of 1/2 way between them.
Make sure there is a foot of line hanging out of the head to put a bit of load on the engine.
now let your finger off the throttle slowly.
You should be able to get it to stay running as with the idle ( throttle stop ) screwed all the way in it should be running on both the high & low speed jets.
Start backing the throttle stop ( TS) out till the engine slows then adjust the Low jet to the fastest running position then back off the TS some more.
Continue till the head just stops spinning then do the same adjustment with the low jet as done with the high.
If the head starts to spin, back off the TS a little more.
When the Idle Jet is correct you will get a smooth acceleration.
If it speeds up a bit then drops back as you throttle on the Low is a little too lean.
If it bogs down as you throttle on the Low is a little too rich.