Help needed - Husqvarna 55

[atpchas]

I've about run out of ideas as to how to get this Husky 55 running decently. It will start and run for a few seconds, then die spontaneously or as soon as any throttle is applied. When first started, it will run a few seconds longer than subsequent restarts.
See it in action:


First, some background - saw has been worked on before by someone else.
Compression is only around 125 but that should be enough to run.
No scoring on piston, top end looks pretty new and I suspect it's after market.
I've done pressure/vacuum tests - no issues.
Second, what I've done (besides above):
New fuel filter although old one seemed good. Fuel line is flexible with no leaks (pressure tested).
Tried new carb (AM) with no change in behavior.
Put in new spark plug. Has strong blue spark - jumped 1/4" gap.
Replaced decomp with plug to rule out any leaks there.
Have tried all sorts of different carb settings starting from 1.25 turns out on both needles.
Set the gap on coil - it was much tighter than a business card.
There is minor scoring on the FW that suggests it rubbed on coil at some point.
FW key is intact and properly seated.
Any suggestions will be appreciated.

 

[Huskybill]

Clean the spark arrestor

 

[Backstage]

Sounds like you’ve ruled out spark pretty well.

How does the plug look after a few start attempts?

Pressure tested. What and how?

New carb. Is that new new or new to you?

 

[atpchas]

Sounds like you’ve ruled out spark pretty well.

How does the plug look after a few start attempts?

Pressure tested. What and how?

New carb. Is that new new or new to you?

Re: spark plug - have not noted that, what should I look for?
Re: Pressure testing - used Mityvac, sealed intake/exhaust ports - held steady at 7-8 psi; also used MV to test fuel line and carb.
Re: Carb - one on saw appears to be new but I got a new AM carb to test and, as noted, no change in behavior.

 

[Backstage]

For the plug, you’re looking to see if it’s dry or soaked, mostly. That will tell you if it’s a problem because it’s getting too much fuel (and/or not enough air), or vice versa.

 

[dsell]

Can you adapt the mityvac to the impulse port? If so, pull the starter and you should see the gauge flutter. Maybe the aftermarket cylinder or gasket plugged the port. Make sure the impulse grommet isn't sideways. Lay a straight edge across the intake where the carb mounts. They can warp if over tightened. Remove the fuel hose from the carb and draw fuel through it with a syringe or vac container. I had a new fuel filter with a piece of plastic inside that blocked the flow. This also tests the tank vent. 125 is a little low for that saw. Probably too much squish. This is my favorite saw and I rebuilt several.

 

[Kenskip1]

Running to lean. Turn the low side adjustment screw about a half turn counter clockwise. The screw closest to the cylinder.

 

[dsell]

 

[atpchas]

Can you adapt the mityvac to the impulse port? If so, pull the starter and you should see the gauge flutter. Maybe the aftermarket cylinder or gasket plugged the port. Make sure the impulse grommet isn't sideways. Lay a straight edge across the intake where the carb mounts. They can warp if over tightened. Remove the fuel hose from the carb and draw fuel through it with a syringe or vac container. I had a new fuel filter with a piece of plastic inside that blocked the flow. This also tests the tank vent. 125 is a little low for that saw. Probably too much squish. This is my favorite saw and I rebuilt several.

Good suggestions. I'll try to find time tomorrow to check out the impulse. I've used the MV that way in the past so I know what you're suggesting.
Agree on the compression - will try to get a squish measurement while I'm at it.

 

[Backstage]

Running to lean. Turn the low side adjustment screw about a half turn counter clockwise. The screw closest to the cylinder.

Running lean can also indicate a leak. Seal between carb and cylinder?

 

[atpchas]

Running to lean. Turn the low side adjustment screw about a half turn counter clockwise. The screw closest to the cylinder.

Agree with your thinking but I've tried everything from less than 1 turn to almost 4 with no discernible effect.

 

[Kenskip1]

I don't mean to critize but are you certain the small grommet is installed in the cylinder base?

 

[atpchas]

I don't mean to critize but are you certain the small grommet is installed in the cylinder base?

It was there when I tore the saw down a few days ago chasing minor air leaks but I will check it again. Thanks for the reminder.

 

[demel1384]

I have had this situation happen to me a couple times. It ended up being the fuel line was pinched or kinked where it passed through the tank wall. It shuts off the gas once it starts or runs a short time. Some of the after market fuel lines are softer and less rigid than the originals and collapse in the tight area at the tank port. Good luck with your saw.

 

[pioneerguy600]

Any chance you have another module around to swap out? According to my ear that`s spark related.

 

[atpchas]

I have had this situation happen to me a couple times. It ended up being the fuel line was pinched or kinked where it passed through the tank wall. It shuts off the gas once it starts or runs a short time. Some of the after market fuel lines are softer and less rigid than the originals and collapse in the tight area at the tank port. Good luck with your saw.

That's definitely on my list of things to check (and some to recheck). Thanks for the suggestion.

 

[atpchas]

Any chance you have another module around to swap out? According to my ear that`s spark related.

Sadly, no. Most of my meager supply of odd bits is Stihl. A buddy of mine might have something and I'll check with him at some point. It appears that the same coil is used in multiple models (Model 51, 55, 61, 254, 257, 261, 262, 268, 272) so he may have something.

 

[Backstage]

Not sure how it could be spark? He’s getting spark, that’s easily verified. And presumably at the correct time, if his flywheel is intact. Other than checking with a timing light (coil gone insane?), not sure what else you could do on that front.

 

[atpchas]

Not sure how it could be spark? He’s getting spark, that’s easily verified. And presumably at the correct time, if his flywheel is intact. Other than checking with a timing light (coil gone insane?), not sure what else you could do on that front.

Although I've seen spark outside the cylinder, there's always the possibility that spark is not adequate under compression inside the cylinder. I've put that near the bottom of my check/recheck list, but right now I'm looking for anything that anyone sees as evidence for possible causes.

 

[5155]

Similar prob on 51 was the two month old colored fuel line from a dealer.
I placed a clothes pin on the kink overnight and it ran fine next day.
I may have contributed by running line under kill wire.
I'm Not sure the proper fuel line routing?