You may want to take look at the carbs as well, sometime a lean or rich condition can cause this sort of thing. You should have the solid needle (AN nnedles) SU HS2 carbs on your 67 (great year to own by the way) the jet should be about .070" down form the bridge when measured with a dail caliper. Also look at the oil in the dampner, run the same oil in the carbs as you do in your engine. Hope this helps.