Dave,

I have completed the running in of a 53. Top end and idle needles settings are now good, idle is good at 2500 with unhesitating transition to full power. OSF plug and 15% nitro.

However if I set the engine to 5000rpm it soon gets lumpy and stops, or else runs fine for say 20 seconds then just stops. It doesn't speed up. I suspect this may mean the regulator needs adjusting? If so, screw it in or out?

Harry

Update - been out flying this evening after work. The 53 is all over the place. After starting I let it warm up, then disconnect glow plug and slowly go to full power. Get 11200rpm. Go to idle and get 2500rpm, back to full power and now it is just 10200 rpm. I check the main needle setting, it takes 1/4 turn leaner but does not increase the revs, go back out 1/4 turn to where the needle was a moment ago and it runs terribly rich, down to 9k rpm, where a couple of minutes ago it was over 11k rpm, so lean it back 1/4 turn and get at best 10200rpm. Idle, especially fast idle 4 - 5k rpm is hopeless, it either runs fine for about 20 seconds then just stops dead, or starts surging, goes lumpy, loses revs and stops. I have tried the idle needle at every 1/4 turn from fully in to 4 turns out and the only difference it makes is whether the engine cuts after 5 seconds or after 20 seconds.

I will now check the valve gaps again (did this after the initial run in) and replace the plug.

Any other ideas?

Harry