8 percent up is quite a bit. This can vary, but i've found that 2 percent can be roughly .2-.5 change in A/F ratio. 8 percent was at least one full point richer. Thats quite a bit, and prob enough to get backfires out the exhaust with all the unburnt fuel. Raising 2 percent would prob be plenty to richen it up slightly.

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
My webpage: http://eclipsed4evr.home.comcast.net
-1998 Mitsubishi Eclipse RS-T- "Toy"
-1992 Plymouth Laser Turbo AWD(SOLD)
-2000 Honda CR-V(daily)