I need some help in turning an old OS MAX-H engine that i got from a friend. It starts fine at any throttle position but once it try to advance the throttle the engine stops in a couple of seconds. It seems a bit better if I keep the slow starter on. Also if I run it on max RPM I can close the throttle and open it back but if I let the engine to run on medium or low RPM it will die once I move the throttle forward. I use OS A3 glow plug. I am new to the glow engines and appreciate any advice.
Thank you.

are you using this Heli engine on an airplane?
does it still have the big, square heat sink type head?

-Joe

This is an airplane engine. It has regular head and carburetor with one needle and two screws.

Sounds like too rich - close the high end needle a bit. Do it while the engine is running with the glow driver attached. BTW, I'd use an A5 or #8 glowplug.

These are a really great old engine and they came in many different versions for both C/L and RC. Some had a single rear ball race while others were twin ball raced.

If you're using a new plug then I'd say it's just a tuning problem and most likely the low speed mix. Go to full throttle and tune it somewhat on the rich side, try for a quite perceptible drop in revs. Then go to idle for a couple of seconds and pinch the fuel line closed. If it starts dying out immediately then the low speed mix is too lean (which is what I think may be wrong at the moment). If it keeps running and gains revs for a few seconds before dying out then it's a bit rich.

The carb uses an airbleed for idle so winding the screw in richens the mixture by covering up more of that hole in the front of the carb. Winding out of course leans it. If winding the screw doesn't seem to make any difference then check that the hole isn't blocked with dirt or gummy castor.