Fuel union on P2

[RobHomewood]

I am like others looking for a replacement for the fuel union which connects the Lucas reserve petrol switch in top of the fuel tank to the outgoing fuel pipe. 2 of the examples I have show the aperture tapered right down within the union- to something much less than the diameter of the fuel pipe (which is about 8mm equivalent). Another one said to be original does not have this tapered reduction. Can anyone tell me a) if this is original? b) what is it for? and c) would the larger aperture improve fuel supply to the engine?

[luli]

What you describe seems to be the original. This is how it appears in the spares list:

The dark edge is the reduction union, and it is an integral part of the petrol sender. See more here: http://wp.me/pXLKy-iO

[RobHomewood]

Hi Luli
Thanks for your reply. I was more concerned about the internal bore of the union which as you can see here



is reduced right down and whether this will restrict the engines performance? I am still trying to improve my cars performance up hills and wodnered whtehr this was an issue. Maybe this was a post war revision to save fuel?
I have had a new union made to the original spec on left here



but wonder whether I should have the second copy opened up more? What do you think?

[luli]

The nominal inner diameter of the fuel line is 6 mm and the union orifice diameter is 3 mm. It should not cause a problem. Using an electrical fuel pump you can measure the rate of fuel pumping. 0.8 liter per minute means, at 100 km per hour, ~2 km per liter. Most fuel pumps are capable of this figure. Is your car consumption so high? Are you familiar with the problems of vapour locks in Rover P2 cars?
http://www.rover-forum.thersr.co.uk/vie ... pour#p7858

[RobHomewood]

Thanks for the reassurance on the reduced aperture in the union. I havent ever been in a position to have a long run yet to check the fuel consumption but yes it has been high I think. I have just had new valves fitted and one seat as they were a bit burnt away. My problem now though is a continuing air leak in the fuel line. I have remade all the joints several times on the fuel line and on the reserve switch including the dip pipes - this time using Loxeal 18-10 as noted in your blog - but still air bubbles. Curiously the bubbles only appear once the engine has warmed up. Something expanding with the heat? Is it possible that there is a pin hole on the copper fuel pipe? When the electric pump was installed a new line was tee-d off near the tank and raken down the nearside. This is largely inside the chassis member so difficult to inspect for damage etc. Any hints how I can pressure test it in situ?
Rob

[luli]

A common test method is the following: Disconnect the line from the tank and seal it with a plug. Use an air pump (like bicycle pump, tire pump etc.) to pressurize it, and brush soap-water solution on any suspicious part. A leak will show up as soap bubbles. One reason for high fuel consumption may be miss aligned or faulty needle valve in the carburetor, or a wrong type of fuel pump which produces a too high pressure.
See more here: http://www.runboard.com/bpostwarclassic ... 2#post8734

[RobHomewood]

Just been for another test run and things are looking even worse. She set off OK then started dying on the uphill- temporarily- and coming back to life. After a few miles this was getting worse including dying out on the flat and having large backfires. Having stopped completely several times on the hills I eventually got back home. Looking at the clear section of fuel line (after the pump) there was a massive amount of air going through - worse than I have seen before. I would have thought with that much of an air leak in there would be a fuel leak out? And how does the backfire happen when the plugs are presumably banging away all the time?
Any suggestions gratefully received
Rob

[luli]

The best would be to separate the suspects: Electrical or fuel supply? If you can arrange (safely!) an alternative fuel supply (like gravity fed or temporary tank and pump) and verify that the car runs fine with it – you can concentrate on the fuel system. Is your petrol fresh and clean (no water or sludge)? How old is the fuel pump? I had seen behavior like that in worn fuel pumps. The pump gets very hot when this happens. Have you measured the fuel flow rate?

[lakesrally]

A split in the dip tubes would cause the pump to suck air, this is quite common. You need to take the tubes out of the tank to check.

[RobHomewood]

On Sunday unable to find a leak I decided to swap the fuel supply from the electric pump back to the mechanical pump, albeit I had to change what was on the car (from T type to U type) as the diaphragm had perished. And hey presto I took her out for a reasonable run this pm and I think its problem solved. I managed to get up a long hill in top gear at 35 to 40 mph which it has never done before but more importantly it didn't die or fade away. I did the hlll twice to make sure. There was a small hiccup on the last hill to home but that could have been vapourisation as it is a warm sunny evening and the old fuel line is next to the exhaust of course. So it looks like the electric pump was the culprit all along as Lulu suggested in his last message. Thanks for everyones help. I shall keep it on the mechanical pump for the moment at least but maybe replace the electric pump as well. Any suggestions as to the best type/make?