Stihl FS80 brush cutter spitting back through carb

Roger Missildine

LawnSite Member
Location
Alabama
Hello all,
New to the forum, and have been searching the net for an answer to my problem. Hopefully someone here can help out.
About 2006, I acquired a used Stihl FS80 weed eater/brush cutter from a yard sale. The owner told me that it ran, but it had fallen off his trailer and cracked the gas tank. I took it home, JB welded the gas tank, put gas in it and it has ran perfectly up until about 2 months ago.
Fired it up, started using it when I noticed gas leaking from the tank, again... Shut it off, cleaned the tank area, more JB weld. Never started again.
Now I'm pretty mechanically inclined, spent over 20 years in the Navy as a diesel engine mechanic, have rebuilt several 2 stroke and 4 stroke ATV and motor cycle engines as well as a couple of tractors. Enough background...
About 2 weeks ago, I decided to tear down the FS80 and see what was wrong. Every time I tried starting it, the plug would be wet, I figured lack of compression. Bought a new cylinder and piston kit. The old cylinder and piston didn't look bad, no scores or scratches, but these are small engines. Put the new piston in, arrow facing the exhaust port, slipped the cylinder on, reassembled with new gaskets. Cranked it over, compression felt low, don't have a tester, but I read that there should be around 130lbs of compression, or blow your thumb off when pulling it over, nope. So, I put about a teaspoon of 2 cycle oil in the cylinder, and cranked it over several times, let it set, did it again. After doing this for about an hour, I did the thumb test again. Lots of compression. Put the plug in and tried starting. Now it spits back through the carb, and the plug still gets wet.
Any ideas??
As I said, this is a Stihl FS80, akin to the FS80R.
All help will be appreciated.

Thanks,
Roger
P.S. Sorry for the long post...
 

Breezmeister

LawnSite Silver Member
Location
South Jersey
Lots of compression. Put the plug in and tried starting. Now it spits back through the carb, and the plug still gets wet.

Try starting it with the muffler off....
 
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hal

LawnSite Fanatic
Location
Georgia
Are you getting a spark?
 
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R

Roger Missildine

LawnSite Member
Location
Alabama
Try starting it with the muffler off....
Thanks for the reply...
Okay, pulled the muffler, now it fires several times per pull, won't stay running though. Tried the carb adjustment procedure from the manual, it is a single adj screw carb. does make a difference, but won't keep running. So, I'm thinking new muffler and carb replacement or rebuild?
Thanks again,
Roger
 
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Roger Missildine

LawnSite Member
Location
Alabama
I want to thank everyone for their responses. I feel like a total DA for not doing what I should have done from the beginning, like checking everything...
Went to HF, got a cheap compression tester just to see what the compression was. Well, lets just say it was real low. So, I tear it all back down again and after really looking, I see oil on the bottom of the crankcase, and oil appears to be coming from the front seal. So, bad seals, at least one anyway. So I decide to pull everything apart and replace both seals.
I started on the back, pulled the starter driver off, that seal had some cracks, but no leakage. Moved to the front end. Pulled the clutch off, then on to the flywheel. I had a small 3 way puller that fit perfectly. After a few turns the flywheel pops free. I start looking at the crankshaft, and part of the flywheel key is still in the crankshaft...
No big deal I think, I'll get both pieces out of the crank and flywheel and buy a new one when I buy the seals..
Not quite. After getting the piece out of the crankshaft (actually it kinda fell out), I start on the flywheel. No luck. I'm thinking it's welded itself to the flywheel, nope. After looking at the parts diagram again, there is no replacement key. So, apparently the key is part of the flywheel.
Am I right? Anyone seen this before? Is there a fix other than a new flywheel? Any idea what a new flywheel cost?
My closest Stihl dealer is about 30 miles away and I just want an Idea of what kind of money I'm looking at.
Thanks again everyone,
Roger
 

BigFish

LawnSite Fanatic
Location
chesapeake, va
The key is indeed part of the flywheel. Not replaceable.
No idea on cost. Mayhaps fleabay.
 
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Roger Missildine

LawnSite Member
Location
Alabama
The key is indeed part of the flywheel. Not replaceable.
No idea on cost. Mayhaps fleabay.
Thanks BigFish,
I did check on EB, but the ones I saw when doing a close up look appeared to have the same issue, sheared key.
I'm gonna put in a call to the dealer in town today and see if he has one in stock. Surely it'll be cheaper than buying another $200 + brush cutter.
Thanks again,
Roger
 

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