I pretty sure ive got a 6mm copper fuel pipe, pumped by a facet fuel pump, connecting into a short section of rubber hose and then into a regulator to get it down to 3 psi. The carbs will idele ok on the choke but bog down, spit, backfire etc afterwards. Could this be something to do with only running a 6mm pipe??????? Hope not will be a pig to change now

Unlikely
More likely to be a problem with the regulator, presuming you are on carbs. As said many times a bike fuel pump is often more suited

From your pics they look like Keihin CVK carbs?

If so check the seals between the caps, diaphragms & carb bodies, a perfect seal is vital, and leaks produce the results you are experiencing.

Thanks for the reply. Phew, it a relief not to have to change the pipes. Do you use anything to help seal the diapragms. I also made my own inlet manifold gasket from gasket paper, perhaps this may be a problem?

When I had the problem, I smeared the bead on the diaphragms with rubber lube, some people have filled the grooves in the caps and bodies with rubber lube, the result is the same.

Suspect its more to do with the carb tuning. 6mm pipe is s little narrow but will be fine for carbs.

cheers for the reply guys, much appreciated

I would be inclined to say it could be a problem with timing. If your timing is severely retarded it will run fine on idle (especially with choke) but will cough when you try to rev it up as it is still burning off while the valves on the intake are opening. I had this when I bought my pinto and the previous guy had it set at about 12 deg AFTER TDC. A simple twist of the distributor (with a timing light) to put it back where it should and it now idles and revs up smooth.