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Posted by Tom G on May 26, 2006, 9:53 am
> 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.
>
> Questions:
> 1. When I press the primer, should I see fuel squirt into the carb throat?
> (I
> don't.)
>
> 2. Should I have (liquid) fuel sitting in the crankcase, after trying to
> start
> it repeatedly? (I do.)
>
> Thanks,
> George
Not sure about your questions but I had a similar problem with a lawn mower
and garden tractor this year. Lawn mower would only run while pumping the
primer bulb and garden tractor only with full choke until finally not at
all. Had to disassemble the carbs on both and blow all of the passages out
with my air compressor. When put back together they ran just fine. I think
last years gas had jelled and plugged up a vital passageway in the carbs.
Didn't put gasoline stabilizer in last fall as I was in too much of a hurry
to head for Arizona.
Tom G.
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