Petrol Spurting from Overflow

[dave1850]

Hello All
Please may I have some advice. After noting the occasional drip of fuel on the base of the jet assembly of the front carb (SU) of my 1850, I replaced the jet assembly and found the jet to float chamber washer well shredded. Then I started the car and noted fuel leaking out of the front carb overflow. I replaced the float and needle and needle body. I have run the car without incident for a 100 miles or so. But now the problem - the petrol poring from the overflow - has reoccurred. I have removed the float chamber lid, used the "blow" test to check that raising the float stops the air flow, which it does and the needle moves freely. On reassembly the problem then occurred again with fuel coming out of the overflow.

Not sure what to try next. Please, any advice?

regards
Dave

[xvivalve]

Is there any fuel actually inside the float? Similar to tank sender floats they can develop tiny holes (don't ask me how) which allows fuel to ingress and affect the buoyancy, thereby leaving the valve open...

[dave1850]

Hi - I cannot see any fuel inside the float. It's a new one. Would the fuel be quite obvious if I shake the float?

regards
Dave

[Carledo]

Just an off chance, has the fuel pump been replaced recently? There have been some cases of aftermarket pumps delivering about 6psi instead of the regulation 2psi. This plays havoc with needle valves, the only real cure is a correct pump (if you can find one) or a fuel pressure regulator.

Steve

[xvivalve]

The fuel inside the float would be obvious, yes, but if it is a new one and the symptom persists, then it probably isn't the problem...

[MIG Wielder]

I have been reading on one of the MGB web-sites of Viton tipped needle valves giving trouble from new, but I can't confirm this myself. There is even a photo of one installed upside down the owner was complaining of fuel leaks!
However I would check that there are no residues on the surface where the float valve seats against the alloy of the top-cover.
Have you a standard mechanical fuel pump ?
Tony.

[Richard the old one]

Having disconnected the petrol pipe from the float chambers it is very easy to slice a very small piece of rubber off the inside of the rubber connecting pipe when you put it back together and this can then stop the needle valve seating correctly. The only way to be certain that you have got any small bits of rubber out of the valve is to unscrew the valve from the cap and check carefully.

I have also had a case where the holes in the float chamber cap that holds the pin that locates & holds the float in have become enlarged. I was most surprised to discover this but once I replace the cap I had no further flooding problem.

[GTS290N]

I connected the fuel hose to the wrong pipe on the float chamber once, wasn't pretty! Of course you wont have done that, but thought I'd fess up.

[dave1850]

Thanks everyone for the comments and tips.

I'm going to pull everything apart and clean it all. As GT has 'fessed up so shall I - I have no inline fuel filter. There I've said it and I have one ready to put in. It's just I have run the car for 15 years without one and without problems - till now.

The fuel pump is the original one as is the rest of the car bar electronic ignition.

regards
Dave

[Mahesh]

A good clean may help, as the rubber fuel line sections are probably flaking off.

Happened on mine with incorrect hoses, changed the spec.

[trackerjack]

Before I went over to Dellorto 45's my Sprint would play this trick as did a 1500 HL I once owned and it was due to small bits of debris stopping the needle valve closing fully.
These old SU carbs are pretty crude instruments and are easily brought down.

[TrustNo1]

Check the float arm isn't bent causing the float to catch against the side of the bowl.

[dave1850]

Hello All

A bit of an update. I have cleaned the float chamber, float and needle and replaced the non-standard needle with a standard (Burlen issue) on. Seems to be ok now despite no visible grit around needle housing. Suspicious about the needle...

Thanks for the comments

regards
Dave

[Jon Tilson]

Really Mike? Valvoline in the tank must make it a bit smokey.....

Jonners

[Jon Tilson]

Always got your back...

Jonners