justin_o_guy wrote on 12/31/69 at 16:00:07:I put the 150 in & went & topped it out on the same road. Hit the same MPH, maybe one better, with the 150. So, does that mean its not too lean? If the top end isnt lowered, I am still providing a good mixture? I sure want the answer to be yes. Ohh, BTW, No backfiring, except the occasional little pop when I slap the throttle shut just right.
No, getting the same or better top speed is not a guarantee that your mix isn't too lean. Performance can improve up to a point with a lean mixture, even more lean than you really want it running. While ideal would be maximum performance with the most lean mix that will not cause damage; I always intentionally err a bit towards the rich side just to be sure. Nothing ruins your day like finding out you've burned valves or holed a piston due to getting an engine too hot from a lean mix (or running a hot plug to overcome some rich mix or oil burning problem).
I think Lancer's advice on selecting a main jet is very good. Keep putting bigger ones in until the engine bogs at top end from too much fuel, then step back down one jet size. That should leave you at max power, with little risk of damage from a lean condition. That should be a very good mix with minimum tinkering. Unless you are going racing and need extreme fine tuning; then be prepared to spend big bucks.