SU carb fuel leak

[sulzerman]

Hi all 

Just noticed a constant drip of fuel from the jet on my spitfire's SU front carb.

The jet and needle are quite new. I have cleaned out the needle valve, anyone got any ideas why this is happening?

 

thanks in advance

[Pete Lewis]

yes Triumphs leak oil  SU leak fuel    tis said i have an avid hate of the things but now have two on my Mk2 2000  Pah.

 

I suggest you remove the air piston and look at the top of the jet the fuel should be about 4 mm below the top of the jet 

if its bubbling out the top and then runs down the sides of the jet as there is no seal between the jet and its holder then there's a fuel level problem in the float chamber.  overfilling due to debris in valve ot seating failed , 

 

having been round in circles with a whole selection of float valves on the 2000 including viton tipped  from a ford packet , Grose jets now are hopless,

I picked up a pair of latest SU offering viton tipped  and two new floats yes they worked ...why...

 

on examinationof the float there was some wear of the valve pin indented into the float contact face , this is enough pitch the needle and jam it from sealing cleanly

 

putting the old valves back in with the new floats reverted to working fine, so the culprit was the float not the valve 

 

there stay up floats about but not for HS4s

 

if your float has the metal top pivot bridge you wont get this , just the all plastic versions 

 

hope thats not too much ramble  

 

Pete

[sulzerman]

Thanks Pete I will check the float I have Viton

tipped needle valves fitted already

[Pete Lewis]

and if you fettle the striker face of the float you upset the float height and need a silly size washer ,very thin  under the valve to correct it 

 

some gentle work with some wet and dry may work its not very workable plastic, nothing made much inroads and revert to the dremel disc just made a ,

melted mess...I should stick to leggo !!!!  hence new floats from the piggy bank 

 

           Pete

[sulzerman]

Pete

Checked the top of the float where the tip of the needle touches and there is mark and may be a very small amount of wear. I have changed the float for a spare, hopefully cured the leak, but I

will keep my eye on it

Thanks for your help

[Pete Lewis]

let us know, i  faffed about cursing for ages before i decided to look in detail and the float has proved  an on going success

( still dont like them )

Pete