Stihl FS 80

[djg james]

I rarely have trouble with my weed whip but twice now, it's done the same thing. It starts up and runs fine until it gets hot (using it 15-30 min). Then you have to keep pulsing the trigger or it'll die. Then it finally does die. Won't restart. Finger is still recovering from a pull cord blister from last time. I replaced the primer bulb years ago and thought I might have an air leak from loosened screws. I tightened up on them today, and thinking it was fixed, used it today for a short while. Then it died.

Any ideas?
















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[Squareground3691]

I rarely have trouble with my weed whip but twice now, it's done the same thing. It starts up and runs fine until it gets hot (using it 15-30 min). Then you have to keep pulsing the trigger or it'll die. Then it finally does die. Won't restart. Finger is still recovering from a pull cord blister from last time. I replaced the primer bulb years ago and thought I might have an air leak from loosened screws. I tightened up on them today, and thinking it was fixed, used it today for a short while. Then it died.

Any ideas?
















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Coil maybe,

 

[Chevboy0167]

Will the unit re-start normally after cooling down to ambient temperature?

 

[Squareground3691]

Coil maybe,

I have FS 80 , over 25 years old, runs great , did put a new carb on it last year ,

 

[djg james]

I have FS 80 , over 25 years old, runs great , did put a new carb on it last year ,

Yes this one is about that old or older. Never had a problem with it until now.

 

[djg james]

Will the unit re-start normally after cooling down to ambient temperature?

I used it last week and then I started it cold today. an it until it died. I'm playing with it a little now, but I'll hang it back up in the garage soon and try to restart it this evening to prove that point.

 

[Squareground3691]

Yes this one is about that old or older. Never had a problem with it until now.

Check tank vent to , but sounds maybe coil issue,

 

[djg james]

I used it last week and then I started it cold today. an it until it died. I'm playing with it a little now, but I'll hang it back up in the garage soon and try to restart it this evening to prove that point.

It has been setting about an hour now. I just put a new primer bulb on it and it started right up and acted normal. I couldn't see any cracks in the old bulb but the engine would run until the bulb was empty. It ran dry which I've never seen before.

So I'm going to use it and see it it shuts down again when it gets hot.

Thanks all.

 

[djg james]

Check tank vent to , but sounds maybe coil issue,

I cold not see a tank vent on it (must be one) so I opened the gas tank and tried to start it. No go. Then I changed the primer bulb mentioned in my post above.

 

[djg james]

Spoke too soon. Went out after typing over an hour ago and tried to restart it. Just wouldn't stay running. I'll try this evening.

 

[farmer steve]

Check the muffler screen?

 

[djg james]

Well, I don't get it. Went out an hour ago and started it up. It would idle but as soon as I pulled on the throttle, it would die. Multiple starts and it started running strong. Used it for 45 minutes without issue. Once I shook it and it seemed to run stronger. Sounds more like a gas problem than an ignition. Not that I would know what ignition problems are. So if it acts up again, I'll change the fuel filter/lines and check the muffler screen.

P.S. I did change the spark plug to no avail. Oh, and I left the cover off while I used it for 45 minutes. It's amazing how much heat the cover blocks. I'm icing a burn on my forearm from the heat. May blister in a few spots. So as a warning, don't do that.

 

[stihltech]

How about some diagnosis?
Compression by starter handle?
Does it spin over correctly?
Does it have spark when it quits? How old is plug?

Spray some brake or carb cleaner around intake, cylinder gasket, seals, case half sealant. Any change?
Are the fuel lines intact (no cracks?)
Fuel line bushings sealing?
Vent in the cap open?
Screen in carb clean? Diaphragms soft and not stretched out?
Piston not worn?
Vacuum and pressure test OK?
That is a good place to start.

 

[SteveSr]

P.S. I did change the spark plug to no avail. Oh, and I left the cover off while I used it for 45 minutes. It's amazing how much heat the cover blocks. I'm icing a burn on my forearm from the heat. May blister in a few spots. So as a warning, don't do that.

You are lucky that you didn't kill it by doing this. The shroud is designed to direct the cooling airflow over the cylinder. Without it... the engine overheats.

BTW, I have changed more ignition coils on the 4137 series than any other Stihl. Usually they just stop dead when hot and restart after they cool off. Tape a neon test light to the insulated spark plug lead other wire to ground.

 

[Chevboy0167]

I was gonna suggest this...

https://www.amazon.com/Tech-Spray-1...refix=electronic+cooling+spray,aps,182&sr=8-1

If indeed it is loosing spark, spray this stuff on the coil or the best you can get to it, for a bit and try a re-start right away.

But in your last update, kinda sounds more like a fuel issue..... hmmm.

 

[Vintage Engine Repairs]

One common issue with these is the accelerator pump o-ring. It can give you very weird symptoms. Runs fine cold, then randomly starts to run rich at idle, then lean out, sometimes it will just stall and restarts can be difficult too. If it has one and you’ve checked the obvious like scored piston, spark failing, check that next.