I'm new to the use of gassers in RC aircraft.

The engine I'm running is a 45cc (I think the displacement is correct) conversion. During ground testing the engine will quit after about 10 seconds if I hold the aircraft vertical. Is this a carb Hi-Lo mixture adjustment problem? If not what else could be the source of this type of engine behavior.

Additionally, the engine response to throttle movement in the midrange is unsatisfactory. When the engine is running in the midrange throttle setting it only takes about 1 or 2 clicks on the throttle stick to make the rpm jump from 4000 rpm to almost 7000 rpm. Is this normal?

How do I correctly determine the volumetric displacement of the engine? I beleive that it's 45cc but judging by the fact that it turns an 18X8 prop at 7300 rpm, I suspect the displacement might be smaller than 45cc.

Is it possible that the low top end RPM could be the result of the carb intake is too small for the engine? The intake diameter is 11mm. I spoke with Terry from CH ignitions an he mentioned that his 46cc Poulan engine has a carb intake diameter of 14mm. I'm considering purchasing a different walbro carb with a larger intake diameter. Is this worth a try?

Cheers,

- Marc.