Well!!!! An interesting day today. The new distributor cap and rotor arm and plugs came yesterday, so it was fit everything, static timed the car, adjusted Holly float bowls on car and try it again.......
No change!
not starting, fireing back in carb or exhaust pipe.
so we re-stripped the carb, just in case i had forgotten anything, checked it all and blew it out with an airline. Refitted it, reset float bowls and tried again.
With judicious juggling of the idle mixture, tickover idle adjust and playing with the throttle, we managed to get it running for about 10 minutes - It wouldnt go over 550-600RPM and wasnt firing on all cylinders. Looking into the carb (a bit dicey with the occasional blow-back) it looked like the main jets werent working correctly - more dripping than spraying.
What we believe is happening is that the fuel is being restricted so that it only runs by pumping the throttle pump on the side of the carb, not on main jets, the fuel is only being drawn into the cylinders in varying amounts, which is why it only runs on a few cylinders, occasionally blows back and occasionally fires in the exhaust. The fuel pumps (red tops) were running at 3PSI, so that was increased to 6 - as per Holley recomendations - still no joy. As all the main jets were clear and there is no adjustment, it is a bit confusing as to why there appears to be fuel starvation and, of course, why it has suddenly changed over winter. One thought, after we had finished for the night, was the fuel filter.... I have known them to "jelly" over a winter, so thats a check for tomorrow. It is the only thing at the moment, that I can think of, that would allow good fuel pressure, but low flow to the carb. I cannot think that it can be the carb now. Tiz really weird.