It's 3.5mm as standard, 0.5mm difference as long as it has clips on should have no effect.

Druid

sounds like the fuel tap prob i had.

The wee rubber vacuum diaphram in the fuel tap can get torn or ripped and be sucked into the fuel line and cut the bike out. Took me a couple of hours to find the problem. Easy solution is to cut open the diaphram and block of the vacuum lines, converting the fuel tap to a gravity feed fuel line. If you do that just rem to turn petrol off.

The bike is fixed thanks to everyones kind advice. I checked and replaced the vacuum pipe to the fuel tap. It must have been drawing in air as the ends were split. I used the slightly oversized 4mm fuel pipe as a replacement using a couple of small jubilee clips to secure it on, worked a treat. Road tested the bike and no more problem. Cheers again people, regards

Sprocket