I'm hoping you guys can help me out on this one.

I was at the track on Friday hoping to get to the race today, but with my 5 port behaving the way it is, I didn't want to chance it.

I had it running sweet as a nut, good punch from low and screaming top end with tons of smoke. Only problem is, after 2 laps when I brought it in to check the temps, they were at around the 290F mark. And this with Byron's Gen 2 25% which is supposed to run cooler. Ambient temps were around the 80F mark. Both my needles were some way in at this point.

Any richer on the HSN and she took the whole of the main straight to rev up.

I stripped her down when I got home and took out one of the shims. I also sealed the back plate which had a little seepage on it and sealed the carb neck.

Took her out again today for a bash and to see if these changes had helped. Now she's started doing something she never did before. After a WOT run, the revs take time to die down and it sounds like when your tank is just about to run out and the engine revs up and then settles down to a nice even idle. Just running around at medium throttle and short bursts of WOT, she doesn't do this. I tried adjusting the idle down, but any less than what I have and she won't idle.

I took the head off this afternoon after getting back and the top of the piston is a darkish brown colour and the glow plug indicates to me that she's been running very rich, it's all black.

My temps are still way above the 260F mark and the ambient is about the same.

Where am I going wrong? Any richer and she just won't rev. There's still loads of smoke at WOT. Oh, and there were already two copper shims and a silver shim in the engine, this was after removing the 'break-in shim'. Is this right?