Originally Posted by
PERROTTO
Probably a mixture of your tune and plug. Use nova plugs. C5tgc (for cooler temps) or c6tgc (for hot ambient temps). Change plug and lean out bottom end. Tune top end for good temps. This should set you on the right path.
+1
In Denmark the BTT guys runs c6tgc with 25% nitro. Only #5 in cold temperatures. P3 in such an engine with 30% nitro sounds wrong.