Problem: loss of power when heating up - clues for the cause?

[Rhett Fisher]

If there isn't any misfiring, I would probably discount any ignition problems. From my experience, the flatheads are very susceptible to wear in the fuel pump mechanism i.e. camshaft lobe, pushrod and pump rocker arm etc. Also, a likely contender is the pump diaphragm which might be damaged by this ethanol that's been foisted on us in recent times- I've had to renew the one in my 1936 Austin 7 recently, as the old one had literally crumbled to pieces! Plus I have two motorcycles which I now can't use, as their GRP fuel tanks have gone soft and leak like sieves. Arrrrgh!
Rhett :-)