I built the engine & it has all new parts in it . I bought all my parts to throught Summit racing, & after getting it together & having the problem. I started replacing parts to try to resolve the hesitation problems,when I accelerate the car when Iam driving it. When iI have it in the garage & run the engine performs great, its only under a load when it acts up. I have replaced spark plugs ,spark plug wires,coil, distrubutor,carburetor,fuel filter,fuel pump,& it hasn't resolves the problem,& I have have the distributor advanced to 36 max advance seams to run best there.