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.
(NB: I have removed the spark suppresser screen.)
First make sure the gas cap vent hole is open (not clogged). If that
doesn't do it, blow air back thru the fuel line to the tank. There is
a small filter in the tank, you may be able to use needle nose pliers
and pull the tube out of the tank and check the filter that is at the
end of the tube.
the crab is fouled......usually from leaving gas in the unit
BTDT with a Husqvrana chain saw...exhibited the the same behavior.
not getting gas, runs that short spurt on gas "primed" in
clean the carb, it'll work
I learned this the hard way, paid to have the card "rebuilt"
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.
Your carb has 2 jets. One is the pilot jet which controls rpm's from
idle to 1/3 throttle, the other is the main jet which controls rpm's
from 1/3 to full throttle.
If it runs for 10-15 seconds, we know you have compression and spark,
and spark timing. Therefore, the only thing left to check is Air/fuel
mixture. Most motors won't run 10 -15 seconds from fuel delivered by
the prime bulb, but could I guess. Most only run 3-5 seconds at best.
Have you tried adjusting the needle jet screws (one is for the pilot,
one is for the mani)?
If you have checked the gas cap and lines going to the carb and are
sure they are clear of any debris, then try adjusting the needle jets.
To start, screw them in all the way, then back out 2 turns, start it
up and then adjust the pilot jet at idle speed and the main jet at
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.