Venting of Fuel Tank

[Robin Fairservice]

I have a 1950 Javelin De Lux and when climbing long hills I seem to experience fuel starvation. I have checked and have ample fuel pressure. Possibly I have a fuel tank venting issue. My cap is a locking type, and I cannot see any signs of venting in it, nor can I see any vent from the tank. Any suggestions?

[Forumadmin]

Drill a small hole in it?

[David Morris]

Hi Robin,

Personally, I doubt that the original fuel tank filler seal is tight enough to cause a vacuum in the tank, as the ones I have seen all seem pretty loose.

The first thing I would check is the state of the two little felt breather pads in the top of the push rod covers, on the top of the engine. If these are choked, they can cause excess vacuum in the crankcase, and affect the fuel pump.

The second thing is that modern unleaded fuel seems to cause engines to suffer more than previously from fuel vapourisation. I have wrapped the exhaust pipe that links the two manifolds on my Javelin with heat-resistant asbestos ( or what we are allowed now under H&S rules ) cord and this keeps the heat off the petrol and fuel pump system. You can buy this cord from shops selling wood-burning and gas coal-effect fires.

The third point is that under these conditions you are pulling maximum fuel from the tank. Although you mention that you have good fuel pressure, is this under full load conditions? There is a possibility, with a 1950 car, that the fuel filter within the tank is partially blocked. I have had this in the past, and the trick is empty the tank. Now remove the drain plug from the tank and put a twist drill or similar up through the filter mesh over the pick-up pipe, which fortunately is immediately above the drain plug opening. Obviously, great care needs to be taken to avoid any possibility of sparking as a 'empty' fuel tank is more dangerous than when full of fuel, so use hand tools or a screwdriver perhaps, to render the filter U/S and go very slowly....I have subsequently fitted an in-line plastic filter to catch any 'crud' and it is surprising how often you will need to change these disposable filters.

I hope this is useful, but whatever you do, do take care.

All the best,

David

[Bryan Walker]

Hi Robin,
Did you solve the problem of starvation
My jav. also suffers from starvation and has good pressure (under floor electric pump and pressure regulator with filter bowl). The bowl is emptying under hi revs. suggesting flow rate more than pressure problems. -Blocked pickup in tank?....

I'll start checking this out once I get back from England.

Bryan

[Robin Fairservice]

Thanks for the responses. The problem was occurring last summer and I resolved it; but how I cannot really remember how, except that I had removed an old style glass bowl filter. It had a ceramic, filter body, was made in the US, was probably 50 years old and I guess that it was not orignally on the car. I also removed a new metal can filter later, but that was because of a fuel leak on the connection. I now rely on the filter in the electric fuel pump. The car goes great up hills.

By the way, I had a very hot car one day, and on checking found that the ignition had become very retarded. No idea how, but I reset it and made sure that the clamp was tight, and it ran at 75 C max. immediately after the adjustment.

Which raises a question. Why are the temperature gauges in Celcius? We use Celsius for weather temperatures, so I am quite used to that. It must have frustrated the owners 50 years ago.

[Forumadmin]

Probably because it is easier to remember water boils at 100deg C rather than 212degF