I have the same problem that Eagleone described. My Alpha with Evolution motore will suddenly die in mid-air with 2/3 tank of fuel and when I land it, it starts easily. The Alpha does not come with a manual for the motor that's worth anything so I was wondering what the third screw is on the carb, i.e., the screw on top of the carb that has the little set nut on it (seperate from both the fast and slow idle screws). Should I tweak on this?

No! That is the stop for the carb barrel.

plowboy.
i had to turn the low end screw in about 1 1/2 turns and the high end is all the way in and it is still on the rich side...good luck.. oh yeah it fly's great...spooner

Just in case you are wondering what the stop screw does, it has two functions on most carbs.

1) it can be set to keep the thottle barrel from closing too far and shutting down the engine. Personally, I don't like an engine that I can't kill from the TX, so I back mine out to allow the carb to close fully.

2) It holds the carb barrel in the carb. Back the screw out too far and the barrel will fall out and the engine won't run to well anymore. .

It does not affect the engine running at all

(warning, overgeneralization in there, but it's close enough. In fact, many carbs use the stop screw to also move the barrel left and right as it rotates. This is done with a spiral groove cut in the barrel that the stop screw sits in. This side-to-side movement works in conjunction with the lowspeed needle to control low and mid-range mixture settings. But since the amount of side to side movement is set by the angle of the slot, it's not adjustable, it's something the carb designer either got right or didn't, and there isn't anything to do about it now).

When you say the high end screw is all the way in, do you mean as far as the limiter will let it move, or did you bypass the limiter and screw the needle all the way? I have found that with some fuels and some air temp/density/humidity combinations, the Evo's limit is a little restricting. You can move the needle past the stop if necessary.

I had a student with an Alpha that had all kinds of engine running troubles the other day. It turned out that the factor installed fuel tank had split at the stopper a bit and was leaking air like crazy. Apparently the stopper was way over-tightened at the factory.

I had the same problem, the fuel tank split. Check inside and see if you have fuel around the tank. One other way of checking is check the fuel line running to the carb and see if it has a lot of bubbles in it while it's running.

Sounds like a fuel delivery problem to me also. I would check my fuel lines, tank, clunk, and make sure my tank was wrapped with foam REALLY well to prevent vibration induced foaming during flight, before I started messing with the engine. I had the same problem on a couple of flights after I installed my Evo, and foaming was the problem. I've got an EVO .46 on my LT40, and it runs better than any engine I have ever used in the .46 class.

Foaming problems?

Ad 2 drops of armorall to a gallon, you will never have a problem again.

Jetts