husqvarna 55 just stops after two minutes or so

[Chris_S]

I have an old Husky 55 that I like very much but it is giving me grief.
I like this saw so two months back when it was running a bit rough I decided to give it a second lease of life and did the following:
New piston and cylinder head (it has a decompression valve)
New fuel filter and fuel pipe
New air filter
New spark plug
New fuel tank and oil tank caps
I rebuilt the carb with all new gaskets inc. mounting gasket
I replaced the fuel pulse tube and tube between cylinder and plastic shield
I removed the fuel tank vent and cleaned that
New clutch, oil pump, chain drive sprocket
Removed muffler and checked it was not blocked

The carb Low adjustment is 1 & 1/4 complete turn out, High is 1 turn. I use 95 octane fuel and Stihl two stroke oil, 40:1 ratio.

After all this it started and ran pretty good and I was happy but then the other day (after about 8 hours running time since the rebuild) it just stopped after about 2 minutes use and would not re-start. Previously it would start immediately when hot or cold.

I have spent ages trawling this site for guidance and so far I have done the following:

I checked the spark by removing the plug and grounding it on the engine then turning it over with the recoil starter. I used an automotive spark measurement tool and that says it is healthy and it looks ok as well.
I checked the spark with the switch wire disconnected, then connected and the result was the same good spark.
It was now cold but still would not start.
I tried spraying a bit of EasyStart into the carb but it still didn't fire.
I put a vacuum pump on the fuel line and the fuel flows fine. So on the basis it had a spark and the carb was getting fuel I removed the carb and checked that. It all looked clean, the needle setting was correct and the fuel diaphragm in good condition. I put it back together but it still wouldn't start.
I could see fuel seeping out of the muffler after trying to start it so on the basis it had a spark and fuel I removed the muffler and it started after 8 pulls or so. So I removed the baffle from the muffler, put it all back together and it started second pull and ran happily for 5 minutes or so and I thought it was sorted. I wasn't happy about the fix as it had worked with the baffle previously but decided to try it anyway then as soon as I started to cut wood it stopped after 2 minutes and now won't start.

I am completely stumped. Can anybody help?

 

[pioneerguy600]

I would check the condition of the piston by looking through the exhaust port, muffler removed first. The engine may have scored the piston, it needs good compression to run.properly.

 

[Johny.W]

oem p/c ?

 

[tug]

Couple things I would check is if you removed the flywheel check that it has not rotated past its key. If the saw just flat out dies it is probably spark related. If it would run but bogged down and die, probably fuel delivery issue. Try putting a little fuel right in the spark plug hole and try starting it. I had a 55 that did the same thing it was something in the carb. Theses saws came with ethier a zamma or walbro carb. I had a 154 husky that when the coil got hot it would affect its function, which is the same coil on a 55, check you ignition gap also.

 

[Cantdog]

I had a nice little 51 come in.....the guy really liked the saw and though it looked great he had used it a lot so he wanted it freshened up. I put a new Meteor piston in it, new OEM crank seals, new OEM intake rubber band and impulse bushing. new carb kit/line/filter. The thing ran great...I cut up about a half cord of hardwood to stove length. He took it and had it about a month and brought it back with the same trouble the OP stated. It would start right up and run great for 5-10 mins then just stop and you couldn't yank on it enough to get it started again....sounded like a coil to me as it still had great compression etc. So I got it running and used it a bit and sure enough it died and no restart so I installed a Ducati coil from my 630 Super II that I knew was good....started first flip.....there I says and went out to cut some wood.....about 5 min in she quit and no restart??? I had that saw kicking around the shop for nearly a year.....tried different coils, rebuilt the carb again with long runs in the USC.....nothing worked....last spring I bought a cheap China carb for it. Paid like $13.00 delivered for a carb, 2 feet of fuel line, a filter and new gasket and screw on air filter.....he's had it all winter and burns wood and it hasn't come back yet......so I assume that cured the problem.

One thing to try is a new plug......I've had a plug run fine until it got hot and lose fire but by the time I got it out, grounded it and yanked on cord the plug had cooled enough to show a nice spark.....had a crack in the insulator that would open up and the spark would jump to the side of the plug rather that go to the ground contact. I always try to eliminate the easy/cheap stuff first when trouble shooting.

 

[Chris_S]

Thank you to everybody who replied.

I checked the ignition gap and that the flywheel was correctly located and this was all correct.
Having fitted a new piston and cylinder I thought these would not need to be checked but just in case I tool the muffler off and was horrified to see the state of my new piston. It looked like this:


This was very disappointing as they have had less than 1 hours running since being installed and I spent about 20 minutes gently running them in. They were cheap Chinese items so I guess lesson learned, you get what you pay for. Perhaps I should have run a higher oil ration mix and/or a richer mixture.
But I didn't think this was the reason for the saw cutting out so I cleaned up the old piston and cylinder re-fitted these as they were in a better state that the new ones.. During re-assembly i noticed that the gasket between the carb and the plastic mounting flange was almost covering the tiny hole which feeds pulsed air to the carb. Again I was not sure that this was the problem but I had a new gasket which lined up perfectly so used that.
I also swapped out the spark plug, I was using the new one that came with the piston and cylinder and replaced it with and NGK item.
And once primed it started no problem, I ran it for a while to get hot and it started ok again. Spent some time re-bedding the piston and cylinder, cut some wood, stopped it on the switch and it re-started second pull so i cut some more wood and so far ok.
Now I cannot say definitively what the problem was, perhaps it was a combination of all three things but I think the spark plug is the most likely candidate. If the saw would start I can't see why poor compression would stop it whilst running and not let it start. If fuel flow was restricted why would it run ok for 5 minutes and then cut out and why wouldn't it re-start. Perhaps the spark plug has an internal fault and it grounding when hot. I always use NGK plugs on my cars so I should had followed my own mantra and fit the best.
Fingers crossed the 55 starts next time out.

 

[cus_deluxe]

Sounds like it was leaning out and it was seizing after a few mins of run time. You likely have a leak at the carb bulkhead. I re-read most of this thread, it doesnt look as though you replaced that part? I wouldnt run it anymore until you figure out why it scored the top end again. That plastic carb mount, along with a bad pulse grommet, are the #1 killer of these saws.

 

[earlthegoat2]

Even cheap P&C kits last longer than an hour unless there was some manufacturing defect to cause an air leak.

 

[Cantdog]

Not saying this is you problem but any time I do a new top end I always either pressure and vac test the crank case or simply replace both crank seals. Cheap insurance...but if you don't replace the seals you need to do both tests as a worn seal can hold pressure but not vac. and vice versa By the looks of that P&C after an hour's rather gentle run time....you're getting a lot of extra air from somewhere. These saws are prone to leakage around the intake rubber band and or impulse bushing....but from your first post it looks like those are both new.

 

[pioneerguy600]

 

[Chris_S]

Yes I would have expected a cheap P&C kit to last longer than it has. I didn't replace the plastic carb mount or the pulse grommet as they looked ok. I have just checked the original piston that I cleaned up and put back again and there is already scoring at the top so something is still wrong. Am I right in thinking the scoring indicates it is running lean and the combustion is too hot? Is this at high speed or low speed or both?

The rubber connector between plastic carb mount and cylinder head is new and fits tight. The pulse grommet locates ok in the cylinder head in that it doesn't appear lose and has to be levered out and the bayonet going into it also seems to fit tight - also this part of the carb assembly is isolated from the intake by the diaphagm on the carb side and the piston ring on the cylinder side so logically shouldn't affect it?

If I richen up the H setting then the engine starts to bog down so that implies the carb is getting enough fuel at high speed, the same with the low speed setting. The carb mount bulkhead on the plastic mount looks good i.e. no scratches or warping, and the gasket to the carb is new. It still has the long self tapping screws that screw through the carb and into the carb mount and these appear to hold tight. The exhaust muffler gasket is also new. It does not have a de-compression valve so nothing to leak there. The cylinder head gasket is new and I used a small smear of Hylomar sealant during assembly. The head screws are tight.

I was running a 25:1 mixture after swapping the piston (just in case it wasn't getting enough oil) and I put plenty of new oil around the piston during re-assembly. I also checked the con-rod and could detect no play in the main bearings. As the main bearings appeared good I did not replace the crankshaft oil seals but would these produce this problem?

I don't know how I can test for air leakage at the cab mount. Should I replace the plastic bulkhead and pulse grommet as a test/precaution?

 

[Chris_S]

I have a Mityvac vacuum tester, how do I vacuum test the crankcase?

 

[cus_deluxe]

Yes absolutely replace the bulkhead and pulse grommet, i think $15 or so for the 2, any decent dealer will have these in stock as these are considered maintenance items in these saws. Best way to p/v test this saw would be block off between the carb and bulkhead, and block off the muffler. I use bits of rubber from an old pair of rain boots. Just cut tapered wedges that can slide down in between until they rest on the screws, which means theyll be wide enough at that point to seal things off. Youll need an adaptor to plug in through the spark plug hole.