[njv]

hi
so you havent had to tighten the valves up any amount to kkep the lash in spec , what i was aiming at is a cam going flat but thats a bit serious so lets rule out some simple stuff first!

have you built this motor do you know the condition of the heads ?
can you do a static compression test remember when you do this keep the throttle fully open . do a dry test then wet what are your pressures?

are your ignition parts in good order felt pad oiled new points good cap and wires points gapped set with a light ?

have you had your exhaust system off recently is it correctly fitted are you running a big header with stock heatexchangers?

give us a bit more info we,ll get there!