return pipe

[stagman]

hi guys, i want to put a petrol return pipe in my rover 3.5 engine stag, i am getting vapour locks, and it a bugger to restart even after six hours cooling down. it always start first time cold, been tuned - up. does the pipe have to be a smaller dia, so the pump can cope?. any help please. paul

[RoverP6B]

Hello Paul,

What type of carburettor is your engine fitted with?

The Rover 3500 P6B, fitted with twin SU HIF6 carburettors, the spill return line is indeed very much smaller in diameter than the lines (main and reserve) which supply fuel.

Ron.

[stagman]

hi ron, i have a webber 500 fitted . paul

[crayefish]

Unless it was VERY small diameter I'd imagine you'd need a regulator...

What are others' thoughts on this?

[bigaldart]

Use a bypass regulator, a Holley one can be modified to do it. Have a look at putting a plastic or plywood spacer under the carb with a sheet metal heat shield. That would probably solve the problem anyway.

Alan

[Ian Anderson]

When a fuel return pipe is run (mainly injection) the return should be the same size as the flow pipe (It has to return the full pump flow when the engine is at idle)

Presumably you are running an interruptor (Facit red top / SU or similar) pump.

If so where is your pump mounted?
If in the engine bay the under bonnet temp could cause the low pressure liquid fuel (before pump) to go to gas state and an interruptor pump cannot pump gas (normally mentioned in gumph that they are not self priming)

If this is the case try mounting your pump near the tank (and low level) instead so it Pumps instead of sucking along the long length of pipe (After all they are called pumps and not suckers)

This may mean you do not have to run extra pipes which may not in the end solve your problem

Ian