Model Forum / Radio Controlled / Air Models / April 2004

Hey Gang,
I've got an older FS-120S-E that won't run for more than 15-20 seconds at a
time. (Another FS-120S-E works just fine on the same aircraft). I checked
the gap on the valves, they were fine. I have partially dis-assembled the
engine and carb. Upon disassembly of the engine, I don't think I see much
out of the ordinary. The only thing that seemed odd was after removing the
head, when I turned the crank over there was an audible hiss and a small
amount of fuel seems to come out from a point on one side between the piston
and cylinder wall. If you were looking at the top of the engine, with the
prop shaft being at 12 O'clock, it was coming out at 9 O'clock. Bad ring
maybe? Cylinder walls seem to look smooth. There was a fair amount of thick
fuel residue (looked like green paint) on the top of the cylinder.

Valves springs seem tight (I guess). Have to press pretty hard to move them.
One valve (the smaller of the two) maybe, just maybe, doesn't go as flush as
the other when closed. There did not seem to be a lot of carbon build up. I
have not removed the valves. One of the O-Rings for the Push Rod Covers
needs to be replaced (torn).

Carb looked pretty clean. However, there looks to be a couple of small
cracks in the O-ring of the needle valve, not torn thru though.

It was also suggested to me that the symptoms might be consistent with the
timing being off. How does one go about checking this?

Any thoughts would be greatly appreciated.

Many thanks!
Mike
"Lucky Dog"
www.bealmear.com/dawn_patrol