Ignition advance keeps the timing of firing of the plugs in line with the TDC of the revving motor. Faster it revs the sooner the plugs have to fire in order to fire when the piston is at maximum compression.
Now if the F3 (I had a 1195 49 states model) has no other changes I don't think it would effect gas mileage. Honda probably had the carbs in a leaner position for CA and/or some kind of air injection system/catalyzer in the exhaust and had to retard the ignition to keep it "in synch".
Pipe, jet kit/ air filter, and ignition advancer would have you in better than 49 states tune in a hurry...Mileage may decrease from too much WFT!
Last edited by smileyman; 11-07-2007 at 08:26 AM.