C90Club.co.uk

So 1988 c90 fitted with original carb. Starts fine and runs well but when I stop , turn off after about 30/45 seconds fuel starts leaking from pipe at base of float bowl. Not a constant flow more pulsing about every 20 seconds. Stripped carb and all seals appear good and carb cleaned and blown through. It is like there is a build up of pressure in the top of the carb that then results in venting of fuel. Any suggestions please?

The needle valve can wear and cause leaks replacements are available cheaply

Edit to add Wemoto £6.05

wightegi wrote: ↑

Mon Mar 29, 2021 6:44 pm

The needle valve can wear and cause leaks replacements are available cheaply

Edit to add Wemoto £6.05

Have replaced needle valve, to no avail and the float. Strange thing is the resultant flow is not constant til it reaches an internal level , it kind of’ pulses’.

Check float height as well.

Might be the seat for the needle valve. My trick is sharpen a piece of dowel with a pencil sharpener. Or use a pencil but pull out or snap off the lead.
Poke the point down the shaft to the seat And twiddle it round with your fingers. Give it a good old spin while pressing down on it a bit.

When removed you should have a neat black ring around the point of the dowel. The seat is now polished and should give the needle valve a chance.

Regards the pulsing... probably the tank gassing off, pressure relieving, gassing off etc.

Robing wrote: ↑

Mon Mar 29, 2021 5:26 pm

So 1988 c90 fitted with original carb. Starts fine and runs well but when I stop , turn off after about 30/45 seconds fuel starts leaking from pipe at base of float bowl. Not a constant flow more pulsing about every 20 seconds. Stripped carb and all seals appear good and carb cleaned and blown through. It is like there is a build up of pressure in the top of the carb that then results in venting of fuel. Any suggestions please?

Check the tank vent is clear. Easy way to test it it to open the tap with the filler cap off or at least undone. If it flows freely with the cap off, there’s your culprit, maybe.

Thanks all for the advice, will be trying again tomorrow! Get back to you with results