Stihl FS36 string trimmer. Walbro carb, diaphragm pump.
Sad story: starting last year, it would lose power after running for 15 mins or
so. I could usually keep it going by nursing the throttle for a while, after
which it would return to normal power for a few minutes, and then do they same
thing again. This year, it did that same thing the first time I ran it; but,
after that, it would die after running for about 30 seconds. I restarted OK,
but then just died again.
Spark seems OK, but I replaced the plug anyway. No help.
I got a carb rebuild kit, and replaced the filter, needle valve, and the fuel
pump and regulator diaphragms. This was a 'learning experience', and didn't go
that smoothly; but, I got it back to where it would ... do the same thing -
start, run 30 secs, die.
Then, I took out the high-speed adjust screw. (Not gummed up.) Since then, it
won't start. Alas.
The needle valve appears to be working: if I pump the primer bulb with the
regulator diaphragm removed, nothing comes up out of the needle until I press on
the actuator lever; when I do, fuel wells up into the regulator chamber.
AFAICT, the regulator diaphragm is working: if I pump the primer with the carb
assembled, it gets fuel to the regulator chamber. And, if I don't pump the
primer, the regulator stays dry. However, I could be confused about what I'm
seeing, or how to interpret it.
Any suggestions would be appreciated.
1. When I press the primer, should I see fuel squirt into the carb throat? (I
2. Should I have (liquid) fuel sitting in the crankcase, after trying to start
it repeatedly? (I do.)