Classic cars forum & vehicle restoration.

Ray White · Joined: 02 Dec 2014 Posts: 6304 Location: Derby

I have a (non original) electric fuel pump fitted to my 1926 Dodge Brothers tourer. I have noticed an air bubble about 1" long (which I can see in a clear section of pipe at it's highest point). I think what is happening is that while there is no problem on tick over or driving for a couple of miles after a period of time this bubble may be getting drawn into the pump and causing fuel starvation.

How can I purge this air bubble from the fuel line?

peter scott · Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh

Ray,

You don't say which side of the pump it appears but if it is on the input side then you are probably drawing air somewhere between tank and pump and need to tighten a union or two.

I can't think why it would appear at the output of the pump.

Peter
_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

Ray White · Joined: 02 Dec 2014 Posts: 6304 Location: Derby

Yes Pete. It is on the input side. There is no evidence of a leak at the tank and there are no unions apart from where the clear plastic pipe is pushed onto the copper pipe and onto the the pump on the firewall. I must have got air in there when I put on the pump but I don't know how best to purge it.

peter scott · Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh

If you are confident that the plastic to metal joints are free of air leaks then try tightening the unions above the pump.

You don't have to purge the air. The pump will do this. You just need to stop air being drawn in with the petrol.

Peter

_________________
http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon

Ray White · Joined: 02 Dec 2014 Posts: 6304 Location: Derby

Thanks Peter..

I will have to look at it again. I will report on progress.

Ray.

Ray White · Joined: 02 Dec 2014 Posts: 6304 Location: Derby

I think I have sorted the problem. There is a small clamp which was at the extent of it's adjustment but not tight enough. I placed a small piece of brass shim stock under it and managed to get it tight. I see no more air bubbles so hopefully it will be reliable now.

Thanks Peter.

colwyn500 · Joined: 21 Oct 2012 Posts: 1745 Location: Nairn, Scotland

The bubble could well come back and I think it will do no harm. It's likely to be fuel vapour which will rise to the highest point. It happens in central heating systems when water-vapour collects at a high point in the pipes even when the system is sealed. A good plumber will put in an automatic vent in that case but obviously you can't do that.
It may condense as it cools but the carburettor bowl should give you enough of a buffer if there are temporary "blips" in supply.

Ray White · Joined: 02 Dec 2014 Posts: 6304 Location: Derby

I have at least stopped any air from being sucked in now. I still have an electrical gremlin to sort out but that will have to wait until I get the car back from Wilkinsons of Derby who I am hoping will make a good job of fixing some damage to a back wing. They have a good reputation.