Mechanical v Electric fuel pump?

[Roger Morrall]

Originally Posted by dwomby

. it's only managing 2.5PSI !!!!!

I don’t understand why you would need any more - that’s around the same pressure as is produced by the SU pumps on the later models. What you need is volume, which is not the same as pressure. Bear in mind that the Carter Carb literally just dumps the contents of the float chambers straight into the manifold on kickdown and you’ll see what I mean.

I found the SU double ended pump that I used to replace an extremely noisy Facet to excellent. Quiet in that it was inaudible with the engine running, even at tickover, but just loud enough to give you that reassuring tick tick as you turn the ignition on. Mine did me 20 years and never gave me any trouble at all.

[dwomby]

Originally Posted by Roger Morrall

I don’t understand why you would need any more - that’s around the same pressure as is produced by the SU pumps on the later models. What you need is volume, which is not the same as pressure. Bear in mind that the Carter Carb literally just dumps the contents of the float chambers straight into the manifold on kickdown and you’ll see what I mean.

I found the SU double ended pump that I used to replace an extremely noisy Facet to excellent. Quiet in that it was inaudible with the engine running, even at tickover, but just loud enough to give you that reassuring tick tick as you turn the ignition on. Mine did me 20 years and never gave me any trouble at all.

Thanks for your input and you may well be right, Roger, but I ordered a replacement pump anyway. The one on there should have been putting out 12PSI and 140 USgph. For what it's worth, my carb isn't the Carter - it's a Summit Racing M08600VS. Also, I tested the pump later to empty the tank. The flow from it seemed rather pathetic but I did not measure it except that it took over 5 minutes to fill a 5 US Gallon container so approx. 48 Impgph? That almost certainly would have been adequate but I decide to replace it anyway. The SU pump was tempting but a bit pricey here plus the one I have ordered physically fits the mounts of the one I have removed.

David

[DODD]

I agree with Roger on all points. As noted in one of my previous posts when my SU stopped working, as a temporary measure I fitted a Facet pump. It did the job but I disliked the noise it produced, despite the insulating and sound proofing I did during its installation.

David W: have you checked the petrol supply pipe to the carburettor which runs along the chassis? The location of the fuel pipe is conveniently situated for it to be trapped by an unsuspecting mechanic when jacking up the car.

Irrespective of what pressure you have in the pump, the flow will be reduced if the pipe has been squashed or deformed.

Brian

[dwomby]

Originally Posted by DODD

I agree with Roger on all points. As noted in one of my previous posts when my SU stopped working, as a temporary measure I fitted a Facet pump. It did the job but I disliked the noise it produced, despite the insulating and sound proofing I did during its installation.

David W: have you checked the petrol supply pipe to the carburettor which runs along the chassis? The location of the fuel pipe is conveniently situated for it to be trapped by an unsuspecting mechanic when jacking up the car.

Irrespective of what pressure you have in the pump, the flow will be reduced if the pipe has been squashed or deformed.

Brian

I have the car on stands at the moment, so I will take the opportunity to inspect the full length of the fuel supply pipe. Thanks.

I really hope to get this car back on its tyres by the end of the week even if I don't do all the little jobs that I had planned while it was on stands. This time of year is best for driving fun here in Florida!

David

[roybatute]

An electric pump will keep running as long as it has power even if the engine has stopped because the fuel line has ruptured...

[dwomby]

Originally Posted by roybatute

An electric pump will keep running as long as it has power even if the engine has stopped because the fuel line has ruptured...

True but there are a couple of preventative systems: you can fit an oil pressure switch that cuts power to the pump if there's no oil pressure; and, you can install an inertia cutoff switch that cuts power if the car experiences an impact. I have the latter installed but plan adding the oil pressure switch at next oil change.

I don't think any car with an electric pump can be considered safe without at least one of those cutoffs installed.

David

[David C]

That's an interesting idea but needs some refinement. If you just use a pressure switch then you will get no fuel until you crank long enough to build oil pressure. A less ideal solution than a mechanical pump.