I have a Irvine 72 which I have recently bought is giving me some problem. When the throttle is advanced from idle to full the engine sinks and tries to stop but when the throttle is moved back the runs at low speed normal. It sounds like that somebody squeeze the throat and it becomes difficult to respirate.

So what could be the possible reason and remedy for this.

It sounds like the low end is too lean. Open the low speed needle 1/8th turn and see if it gets better. If its better but still doesn't transition well, open the needle in small increments until it does.

Solved the problem...

It was the plug... I think the OS # 8 is the only best plug that is reliable. Other gets " WEAK " after some time and the transition response does't remain consitent.

eastmoney...next time you buy a new engine use the oldest plug you've got when you run it in. Running in essentially means that tiny bits of alloy can get on the plug coil and this will ruin the plug.