i have a 1995 GMC rally STX van (G2500 3/4 ton) i had to rebuild the engine and since i was going to be using for some light towing i purchased the comp cam XE249H-12 and had the engine bored to 4.020.. my question is this..will either of these effect the stock tuning?
when i first fire the engine up it's burning so Rich that inside the exhaust pipe tip is nothing but black soot..i monitors the O2 sensor with a DMM and it starts out at around ~ .5 or .6 and climbs to just over .7V before the ecm goes into closed loop.
the idle is really rough and the O2 stays for the most part right at .7V on the high end and bounces down to around .02V on the low end..and still the mixture is rich..

I pulled the vacuum line off the brake booster to try and see if it would lean out with the extra air added..but it was a no go..

which is why i'm wondering if the cam and bore has altered anything..
the only thing i can see in tunerproRT with bin file BJYN is a setting to set CID which if my math is correct would be 44.16(44.28 in tuner pro) but would that be enough to make it run rich?
or is there other things in the ecm that need adjusted?

Thanks Rick