Fuel starvation -firdt observation - do you agre or...

[davidf]

I had these symptoms once, many years ago. It lost power, but did not stop completely. If I stopped to 'play' under the bonnet, it would rev freely under no load, but not pull unless it had stood for some time ticking over. So I thought - 'not fuel pump failure'. As my journey home from where it happened was a few miles on main roads, with a few right turns across busy traffic, I decided to stop and call the AA. It limped into a lay-by, and I immediately switched off.
The AA man listened to my detail of symptoms, and said - it must be one carb not filling properly; float valve not opening fully. When you are standing, it fills slowly, and then runs normally till that carb is drained. That puts you into one carb working, and one pulling air, which makes the mixture very weak. Hence it will rev under no load, but not pull.
He proved his point by taking the tops off both carbs, getting a long length of soft plastic pipe, pressing it against the main jet of each carb in turn, and sucking. One had fuel in it, the other was dry.
He suggested getting a recovery vehicle, but I said it would be OK if I flicked off the linkage to the dry carb. We did this, and it drove home quite normally (although probably would not have made the normal 0-60 time). I stripped and cleaned the float valves, and all was fixed.
However, you could also get this if the feed pipe to one carb was rotting on the inside (restricting flow).

[HersnotHis]

Update - I think the inertia switch may be to blame.

Folowing suggestions by others I removed the inertia switch. Examination showed that the plunger was very loose and scrapey on movement. Could not dissassemble as per the link DJT posted as it appears to have been glued together with Araldite or similar.
So I made up a bypass of a short lead with spade terminations. I also noticed that the 12V supply to the Lumenition Ignition electronics was derived from the lead to the pump side of the switch by a somewhat crude strip, twist and tape type connection. So I think the pump operation may have been compromised by a poor contact in the switch with the double jeopardy of consequently poor supply to the electronic ignition!

With the bypass in place I removed the fuel connection from the carb side of the pressure regulator and put a short length of plastic pipe into a bottle Turned on ignition and bottle half filled in seconds.

Reconnected fuel supply. etc.

Set off and car drove perfectly for 9 miles!

So hopefully this is the answer.

If I cannot get Inertia switch apart will get a new one.

Thanks to all

H

[Stagnant]

Hi H

See the 'fuel cut off switch' thread.

Cheers,
Mark.

[DJT]

Same as Stag:

http://www.ebay.co.uk/itm/JAGUAR-DAIMLER-SERIES-2-XJ6-XJ12-FUEL-CUT-OFF-INERTIA-SWITCH-C41220-/151122629038?hash=item232f9c51ae:g:R-4AAOxyQj9RXY9l

[HersnotHis]

Thanks for additional info Stagnant and DJT .

H

[Robmsharp]

I had a similar issue - not quite as bad with my symptoms but it turned out to be the fuel pump not being able to keep up with the demand. The cure was to fit a new pump (got an electronic one from LD parts) and the car has been happy ever since.

[Escape]

My experience with a failing fuel pump was just the opposite: it would run OK(-ish) when moving, but stalled when stationary for any length of time. When I stripped the pump (original item, with points) it seemed the piston sometimes got stuck and the spring couldn't overcome the resistance. While moving, there was sufficient bouncing to get some fuel to the carbs, once stationary they would soon run dry. I adjusted the piston as per the ROM, to make sure the rocker mechanism operates reliably as intened and it's running sweet again. Just to be sure, I also rewired the pump to minimize the voltage drop. The inertia switch tested OK when measuring resistance, so I left that alone.