something is going wrong when i try and advance my timing...this is what i am doing... i warm up teh car to normal runing temp... then cut the car off pull the one sensor hooked up to the distributor crank the car back up loosen teh distributor hook up my timing light on cylinder one... move distributor till timing reads approx 15 degrees on the harmonic balancer... tighten the distributor back down and check again and still reads 15 degrees... cut teh car back off and plug the sensor back in.. timing now reads 20 degrees???? let ideal drive it around teh block come back timing still reads 20 degrees??? there was no valve tap or anything while the car was runing at 20 degrees... what is cause ing the jump up to 20degrees?