One of my friends is always having this problem with his GMS .47 . It could be a wrecked carburettor, or poor tuning.

IT seems that when I place the plane vertically and do full throttle, the performance dips, but this doesn't happen on half throttle.

Wot problem is he having?

Probably running the engine too lean.

When tuning the engine on the ground, you should use the needle to get the maximum RPM without going too lean, AND THEN BACK IT OFF A CLICK OR TWO. In the air, the prop will gain RPM because of the airspeed of the plane (the prop does less work in the air than when the plane is stationary on the ground). Further, when going vertical, the suction produced by the carb that pulls the fuel into the engine has to overcome gravity, as well as G'Forces to get the fuel. Thus, you engine over-leans and starts to die out.

Wou will not have this problem at half-throttle.

gus

Gus is right on, you are just too lean. At mid-throttle, the lowspeed screw is playing a part, and it's not set as lean as the needle, so the problem goes away. That bit of info has me totally convinced that it's just the needle setting. Carb problems and such tend to be worse at lower RPMS, not better.

The high speed needle should be set with the nose pointed straight up.

arg. i dont know how to work the high speed needle.

Yes!

Turn it out = richer. Turn it in = leaner. You need to turn it out while somebody else holds the plane up. Keep the prop above you head and put the engine at full throttle to adjust the high-speed needle. It's easy. Just turn it and you'll see what happens.

If you find that holding the plane nose-up and adjusting it in that position is a pain, you can adjust it with the plane level. Start with the needle backed out a little (rich), then slowly move it in, a few clicks at a time (leaning the mixture). Give the engine time to "catch up", needle changes are not instant, the engine takes a second or two to react. As you move the needle in, you should hear the RPM increase as the mixture leans out. Once it stops increaseing, you are at peak. If you move the needle in more, you will hear the RPM start to drop off a little as the mixture is now too lean. Back the needle back out, and set it a little on the rich side of max RPM. Now, pick the airplane up and point the nose up. If you hear the RPM pick up just a little, you're perfect. If the RPM drops at all, you are too lean, back the needle out just a little. If there is no change, you are right on the boaderline, so you should probibly back it out just a little.

If you don't want to pick the plane up, you can also give the fuel line a pinch. If the engine picks up RPM, that's good. If it looses RPM, then you are too lean. I find the nose up test generally more reliable, but I use both, depending on the plane.

On trainers, I frequently just lean it out until I think it's near peak, then back it out a bit from there. I don't need max power and staying a little rich is easier on the engine anyway.

All adjustments here are done at full throttle. Be careful, take your time, and watch that prop.