These engines run much better with nitro. 5% is enough. Your engine if slowing down and quitting can be two things; 1. too lean but I doubt this. If the idle needle is too lean the engine will slow down and stop at mid throttle with the old carb. 2. so rich the plugs load up and quit with fuel slobbering out the exhausts. Do not be afraid to play with the needles with the engine running. At high throttle, lean out to full rpm and then back off to 500 or so rpm less. An unbroken in engine will be fine run up to full power with the needle for less than 5 seconds. Then your needle will not be ridiculously rich. You need to train yourself listening to the engine under different needle settings. Now the idle. Throttle the engine down to a reasonable speed like 1800 rpm. Adjust the idle needle opening and closing to hear what the engine is doing. Get it to idle reasonably steady. After a couple of hours with 10 minute runs start dialing in with lower idle and higher leaner settings at full. With a fully broken in engine the top end is STILL set fully for highest RPM and then richened to slow down 200 or so rpm. The idle as you adjust down to lets say 1200 rpm will require readjusting the idle needle. It is critical to keep all wired as absolutely short as possible and thick. You are dealing with 1.3 volts and even the slightest resistance drops the voltage a lot! -Tom