Vortec, I run at sea level in New Jersey. The reason I went with the 170 is because thats what most people were running with the slip on K&N and I figured I'd rather be a little on the rich side than too lean. Runing lean burns up pistons, a little rich at worst will foul a plug. But it doesn't blow black smoke or anything so I imagine it's close to where it wants to be if not right on the money. I'm not the biggest believer in checking the plug after each jet change, it's not accurate enough in a single cylinder engine IMO. I haven't yet pulled the end cap off yet with the jet changes, I might try it tonight. For you guys debating the Dynojet kit, I don't think it's worth the jingles, I was pressed for time when I bought it and I think the scumbags at my dealer were just blowing smoke when they said they didn't have individual jets so they could rip me off for $65. I have it set up in the stage 3 configuration (God, sounds like a fast and furious ad) but thats the dynojet needle in the #2 position, 170 main jet, I cut 5 coils from the spring, drilled the slide holes to 1/8", and my 50 pilot jet is on the way, and 3 turns out on the mixture screw. Hope this helps you guys. Oh yea, if you do all this, hold on tight, 2nd and 3rd gear are completely different