Carb leak from float bowl pipe

Are you new to the forum? Please come in here and introduce yourself, please don't forget to check out the rules as well!
Post Reply
Robing
Posts: 3
Joined: Sun Jan 31, 2021 6:58 pm
Rides:: 1988 C90G, bmw gs, bmw rs
Location: Aberdeenshire

Carb leak from float bowl pipe

Post by Robing » 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?

User avatar
wightegi
Posts: 8715
Joined: Tue Sep 01, 2009 7:23 pm
Rides:: 12v 1988 e start C90, Gl5oo silverwing ,Piaggio xevo 250ie
Location: Isle of Wight

Re: Carb leak from float bowl pipe

Post by wightegi » 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 :)

Robing
Posts: 3
Joined: Sun Jan 31, 2021 6:58 pm
Rides:: 1988 C90G, bmw gs, bmw rs
Location: Aberdeenshire

Re: Carb leak from float bowl pipe

Post by Robing » Mon Mar 29, 2021 8:33 pm

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’.

Harps18TV
Posts: 169
Joined: Mon May 01, 2017 7:16 pm
Rides:: 1960 Lambretta TV175, 1990 C90, 2006 MD90 & 1978 CG125.
Location: Harwich

Re: Carb leak from float bowl pipe

Post by Harps18TV » Tue Mar 30, 2021 4:22 pm

Check float height as well.

User avatar
Newtsalad
Admin & site janitor.
Posts: 17104
Joined: Fri May 01, 2009 8:30 am
Rides:: XL1200c, Cali III, R80RT,GS750,XV535,XL350,BN125,C90's,C200's,CT200,Little Cub's
Location: Essex boy loose in Suffolk!

Re: Carb leak from float bowl pipe

Post by Newtsalad » Wed Mar 31, 2021 7:59 pm

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 :shock: :o :shock: :lol: 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.

slowboy
Posts: 370
Joined: Fri Nov 02, 2012 9:48 pm
Rides:: Honda C90e 1986, Honda Super Cub 125, Yamaha FZS600 Fazer
Location: Kingsbridge Devon

Re: Carb leak from float bowl pipe

Post by slowboy » Wed Mar 31, 2021 10:30 pm

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.

Robing
Posts: 3
Joined: Sun Jan 31, 2021 6:58 pm
Rides:: 1988 C90G, bmw gs, bmw rs
Location: Aberdeenshire

Re: Carb leak from float bowl pipe

Post by Robing » Wed Mar 31, 2021 10:38 pm

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

Post Reply