Air in the fuel line

[RobHomewood]

I am trying to recify air in the fuel line on my p2 which leads to an intermittent faltering and dying when out. I have relined the fuel tank and have a persistent air leak somewhere I cant find. It only appears when the engine has warmed up and I can only reproduce it when stationary by revving the engine then letting it drop back after which the bubbles appear. ( I have introduced sections of clear pipe before and after the electric pump) I have remade every joint on the system including the branch to the old mech pump position -now disconnected- but cannot eliminate it. I have also reset the dip pipes into the reserve tank switch unit. Why does it only leak in these circumstances? Any suggestions gratefully received

[luli]

This may help: http://wp.me/pXLKy-1nF

[Phil - Nottingham]

Excellent advice

[RobHomewood]

Thanks again Luli. I had read your blog page before but reading it again made me think I should try the Loxeal thread sealant rather than the PTFE etc. Well I couldnt get Loxeal locally and it would take a week or so to deliver apparently so I got some Rocol OIl Seal which seems to be up to spec. I shant be able to test the result until tomorrow so fingers crossed until then
Rob

[RobHomewood]

Not good news. The remaking of the fuel line joints and dip pipes did not cure the air leak. So I have replaced the in line filter (and pipe sections) just before the pump as I could see bubbles after that but not able to see if they were there before. Another wait until tomorrow as the thread sealant goes off.
Has anuone any experoince of this Rocol Oil Seal which I am usng? Not surprisingly I am having doubts about that now.......

[lakesrally]

I had a similar problem on my P3 a couple of years ago. The fibre washer at the fuel tank take off was the wrong size, it had been air tight for about 15 years but eventually it failed and started to pass air. Worth checking that is is a tight fit.

[RobHomewood]

Thanks Stewart . My adaptor onto the reserve tank unit take off uses a copper washer which I presume is standard for the P2. I have remade that joint along with all the others more than once. Still getting air bubbles in the pipe before the pump despite new filter & joints etc. I am stuck for any answer
Rob

[chris dancey]

Hi Rob,

I am in Cyprus at the moment and don't have access to my files, what model and year is your car ? If you have an early car with the cork seal type piston reserve switch that screws to the top of the petrol tank then this is generally a problem area, the cork pistons can shrink to allow air through and create the exact symptoms you describe.

[RobHomewood]

Hi Chris
The car in question is a 1939 14 DHC and has a cast reserve switch/ dip pipe unit which is screwed down onto the tank with 4 set screws. It has a cork gasket between the unit and the tank but that is just to seal the fumes into the tank and is not in the fuel system as such. The reserve switch unit is one which I salvaged and made a new mesh filter for as the original had been soldered, cut and bent presumably due to earlier air leak problems. The replacement had not been used for many years I think but the solenoid worked OK. I didnt fully dismantle it to see the condition of the moving ball/piston but even if that were not sealing 100% it would not let air into the system unless the fuel level was low which it is not.
Currently I have embarked on investigating the poor power as someone is available to work on it and he has taken off the head . Valves are looking poor and the gasket probably leaking between the bores so hopefully that will be resolved soon and I can then get back to pondering on the air leakage problem.
By the way my man is suggesting putting valve sleeves in if he finds the valve seats are in bad condition so that I can use unleaded without additives. Any advice on that?
Rob

[luli]

One way to detect leaks is to pressurize the line with air, cover any suspected joint with soap solution (or just immerse it in water) and watch for bubbles. This is done with the petrol reserve unit out of the tank and the mesh removed.
Mike Couldry has everything you need to convert your head to unleaded: seats, valves and valve guides, even new springs. You can watch some pictures here: http://wp.me/pXLKy-2lJ.