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On Tue, 05 May 2009 22:24:55 -0400, George
wrote:

On Tue, 05 May 2009 22:09:49 -0400, wrote:

On Tue, 05 May 2009 16:22:26 -0400, George
wrote:

I have a Stihl FS36 trimmer, which has a Walbro diaphram carb.

It starts OK (after priming), but only runs for 10-15 secs before
rapidly losing power and dying. After it dies, I can restart it (after
pumping the primer bulb), and it does the same again.

IMO, it acts like it's not getting gas. There's no smell or other
evidence of it flooding. But, (a) pumping the primer bulb while it's
dying doesn't seem to help; and (b) when I take the carb apart post
mortem, there's gas in the chamber under the diaphram. Also, when I
operate the needle valve, gas flows up into that chamber. So, the gas
seems to be there.

Any thoughts would be appreciated.

Thanks,
George

(NB: I have removed the spark suppresser screen.)

Jet plugged.

I wondered a little about that. But, during its brief burst of life, it
seems to have full power, and good throttle response. Would you still
think the jet?

Sure sounds like it. Carbs usually have several jets. One for idle,
one for midrange and sometimes more. Your mid-range jet is very likely
clogged. Enough gas dribbles past it to make the engine rev for 10-15
seconds, and then it starves. It's the same performance you would get
by sqirting some ether in the throat and then starting it. As soon as
the ether burns of, the motor dies.