engine runs then stalls

[kibris]

Glad you got it sorted - I think the overflow is designed to be open to the atmosphere and by plumbing it in to the fuel return it back pressures and causes your symptoms. Anyway dont worry about the reasons its works thats the main thing

[Anton]

I was thinking of making a fuel overflow return, but perhaps not after reading this thread!

[timwilks13]

Did a bit of reading up on SU's last night in my old school 'AA book of the car' i found in my dads attic, its a fantastic book describing how pretty much everything in a car works, and it has a section on SU carbs and you're right Kibris the over flow from the the float chamber is designed to be open, its a fuel overflow, not a fuel return, very different things.

[ScottieJ]

Just to bring up an old thread.

Anyone who has a long pipe on their overflow hanging down low might want to rethink and route it somewhere else.

I'm 99% sure mine dangling into the water while wading was the cause of my sj cutting out in water over the weekend

[twiss]

I've got a 1 way valve on the end of mine

[Darrell]

Under 2ft of water kinda blocks it of

[ScottieJ]

I've got a 1 way valve on the end of mine

A one way valve on something that needs to vent both ways?? it allows air in during normal operation but If your float sticks where is the fuel going to go if it cant get out?

[twiss]

The valve lets fuel out but nothing in. Haven't noticed any problems since I put it on...

I did have the overflow going to the valve and then into the fuel return line but I've just blocked that off now

[ScottieJ]

Twiss this whole thread is about how it needs to be vented to atmosphere if you block it off you get running issues, maybe it doesn't draw enough in to shut off the valve, however if you block them off or run them into the fuel return most people seem to get issues.

If I block mine it stalls almost instantly, as it does on trotters and my fathers.

[ScottieJ]

Another cause of flooding, often mistaken for an over high fuel pump pressure, is caused by air trapped in the float chamber. When fuel is fed into the float chamber it rises and the float shuts off the needle valve. If, however, the chamber air vent is blocked, the fuel rising compresses the air in the chamber and fuel is forced out of the jet at pump pressure.

There are several different methods of venting the float chamber, from a simple hole in the lid to overflow pipes, all of which can be blocked in various ways. If in doubt, loosen the fixing of the float lid just enough to allow air to escape and see if this cures the problem. If it does, then hunt down the blockage and remove.