The Bis started playing up again with the Polish carb fitted and would not start so back to square one
I decided to fit a Facet electric fuel pump which never stopped running and consequently filled the engine full of fuel to the point of hydraulicing
it was the 1-4 psi version so should have been okay
After a suggestion from Pete126 I checked the feed and return pipes are the correct way round i:e I had blanked off the return and not the feed
Now it is at this point something comes to light and maybe I have got it sorted
Blowing down the return pipe I can feel pressure building up and on releasing pressure air comes rushing back out of the pipe
Remove the new filler cap I purchased and as expected no pressure build up
Next step was to refit the Weber carb I had no end of problems with and also refit the mechanical pump so back to standard
After a few tries she fires up and runs beautifully revving freely all without the filler cap fitted
I assume that the filler cap should be vented and I have been lucky not to collapse my fuel tank
I know this used to be a problem many years ago and have seen fuel tanks that have collapsed but had never even considered it
