Fuel Problems - HELP REQUIRED FAST!

[MaestroMatt]

Hello all. Very peculiar problem with A82 WHR today. I discovered fuel leaking round the end of the hose that goes on the fuel inlet on the carb. About half an hour after turning the engine off, the fuel was still trying to pump out (in short bursts) and it had emptied the entire fuel filter out over the exhaust manifold. When I pulled off the hose, there was a gush of petrol and a hiss of air as if the entire system had been under a lot of pressure. I fitted a new fuel pump a couple of months back but this is the first time this has happened (it has been weeping round the end of the hose on and off though). Why is this happening? Surely excess fuel pressure is vented through the carb fuel overflow pipe...? Could the pump be too powerful for the car? It is not a Rover one, it is a QH one.

[MGTurbo]

An interesting one. The over-flow pipe will only let fuel out if the float chamber fills to excess, normally the float shuts off the needle valve before this happens unless the needle valve has failed due to wear or incorrect float setting.

Simple law of physics means the fuel cannot be pumped if the engine isnt running! This doesnt stop a syphon effect however, especially if parked on a slope with the front end facing downwards. I'd be looking at swopping the fuel pump first and then after that a strip down of the carb to check for blockages and correct levels.

HTH
Gareth

[tony]

not something simple like nipping the clips up?
there should be pressure between the pump and carb,even with the engine switched off for half a hour .especially with a new pump(not letting the pressure back though the pump).the carb over flow is for too much petrol in the fuel bowl to drain away.
i hope i am right about this ,hope it helps

[tony]

only other though i have is thermal expansion of the fuel,if your vent on the cap is not working ,have you changed the petrol cap lately?:(

[E_T_V]

I'd agree with tony. check that the clips are tight. there should be pressure there. Also check for fuel tank pressure too, especially on a hot day.. (Fat chance at this time of year I know)

[MaestroMatt]

What I have done for now is put a new length of hose on that is 1mm smaller in diameter than the other one. This morning it was fine so hopefully this was the simple cure. I am confused though - the other hose was clamped up just as tight but leaked. Could it be that the smaller diameter hose constricts the flow of fuel a bit? After giving it some thought, I remember that I have heard from other R series owners that their cars have 6mm hose from tank-pump-filter-transducer then 5mm from transducer-carb but at the time I foolishly didn't think to compare mine and replaced them all with 6mm hose.

There is definitely value in what Gareth says though - after 20 years of use and with no record in the fairly good service history of any carb maintenance, I think I should set aside a Saturday and strip down, clean, and reassemble the carb. Is there an SU service kit you can get complete with all replacement seals and spring etc? Anyone know which kit I need? I will also check the fuel cap and possibly treat myself to a new lockable one as an early Christmas present.

Thanks for the quick replies - sets my mind at rest that there should at least be some pressure there.

[SimonR]

Originally posted by MaestroMatt
Is there an SU service kit you can get complete with all replacement seals and spring etc? Anyone know which kit I need? I will also check the fuel cap and possibly treat myself to a new lockable one as an early Christmas present.

Yeah there's an SU parts catalogue under the coffee table in front of the TV at home! :)

[MaestroMatt]

Originally posted by F153JUE
Yeah there's an SU parts catalogue under the coffee table in front of the TV at home! :)

Cheers Si, I'll have a gander before we go and play squash. :)

[advantage_d]

The carb on my 1.6 s series did the same. Fuel was sqeezing out of every gap it could, even past the rubber seal on the base of the float chamber. One morning I only got to the end of my road, had a look at the petrol evaporating and had second thoughts.

I imagined it may have been a worn needle valve letting in excess petrol but if that was the case wouldn't it just vent onto the floor through the vent pipe.

p.s. on really cold mornings the auto choke carb would sometimes spill petrol from the vent pipe onto the floor.

Anyway I got a auto choke carb from a 1988 montego and its been fine ever since.