My k5 has been backfireing through the carb and dieseling when I shut it off lately, so i went out to check and adjust my timing today. I have a 350HO with an edelbrock 1904 (795cfm) carb, a accel billet distrub, and an msd6a box. I let the truck warm up to operating temp, disconect and plug the vac line at the distrub advance, and make sure my idle was were it was susposed to be, and hooked up the timing light. and sure enough the timing was off. it was approx 18 degress atdc. and it should be at 10 degress btdc. so i turn the distrub until the propper timing markes line up. and this in turn raised my idle rpms. so i adjust the idle screw until its idleing back down where its susposed to be. recheck the timing and its off again, so i adjust it back to 10degrees btdc, and now my idle is off again, re set idle, now timming is off its just a never ending circle, what am i doing wrong?