OK, i see what you're saying. So no need to increse till i give it more AIR overall.....got it! So the 21cc domes i can still run 91 octane fuel....but with the 20cc domes i'll be striclty race gas.....i'm at sea level and riding in the Dunes out in Gordons Well mostly so the setup i have should be good.....I'll ned to get with NOSS MACHINE to get the low down on his domes and what he thinks. Thanks for the reply!