Denny, you are just going to have to start changing parts and doing a lot of test driving. You have to be brave!!!!
I worked for a year and half trying to get a bad miss out of my 250. It would only act up pulling a long hill, worked great everywhere else, hot or cold. After changing intakes, carbs, ignition, cam, lifters, drive shaft, one axle shaft (bent slightly) I finally changed the head. It turned out the porting I had done messed with the air flow intake to exhaust ratio, the exhaust could flow the same amount of air as the intake side, and on a long hill with plenty of throttle, the exhaust was sucking the intake charged air out when the cam lobes were over lapping. Dad has a Superflow air bench so after rechecking the numbers and talking it over with some head porting guys, they confirmed what we suspected.
Now with a stock head, it runs like a top. I never would have suspected the head, but I was out of ideas. It ran great at full throttle and around town, but try to pull a hill and you would drop from 65 to 35 before getting to the top! It shock so hard, that the Lokar shifter bracket broke.....
Joe
