I have 2 friends that both have the same problem with their 3W 80s,,

on the ground the engines run and idle great, as they should,,

in the air they will not come down to an idle,, they stay at a high idle,, too high !!

this happes at low-speed flight just before landing, the engines idle to high to get the planes on the ground,, richening up the low-end needle only make the engines too rich for flight,,

I have seen it happen to 1 engine, and this engine does not seem to be leaning out,, this engine has a ridged throttle linkage so there is no slop in the linkage,,

any thoughts on this ??

Jim

possible air leak on the carb blocks or the exhaust...... along with u may just be to lean even though it seems rich in flight

High idle is often a sign of lean mixture. So, perhaps it's a leak in the carb mount block, but it could also be that the cowl causes some air pressure buildup at the carb inlet, which would lean the engine and cause high idle. Do these engines exhibit the same symptoms when run without cowls?

If so, placing a baffle in the airstream just ahead of the carb and perhaps increasing the air outlet area in the carb might reduce the cowl pressure and thus the idle.

Also, I suppose air pressure in the cowl could cause the metering diaphragm on the carb to see a different pressure, which could also cause leaning. If you haven't already, consider soldering a short piece of brass tubing to the metering diaphragm cover's little breather hole. Run a piece of fuel tube from the new brass tube into the fuse, where there should be no "ram air" pressure to mess things up.

That's about what I can think of that might cause high idle in flight, if it's lean related. Pretty easy things to try (especially running without the cowl) anyway to try to eliminate possibilities.

J

I had the same problem on my 3w 70. I was told a lot of things, but this is how I fixed it. There is not enough back pressure on the engine. Close off one of your exhaust ports and see if it fixes the problem. It did on mine. To test It, I shoved a paper towel in one side then put a piece of plastic over the exhaust tube to hold it in place. It wont last long, but long enough to see that it works. Once you see that it works, you can either pinch one side closed, or if you want it to look better make a metal cap to go on the other side and use a hose clamp to secure it.

u also are changing your mixute by blocking off the exhaust a tune pipe changes how the mixture exits also.

Mine did the same thing. I used the idle down function of my radio prior to landing, worked great.