Help Jag Mk2 hot engine starting problems

Help Jag Mk2 hot engine starting problems

Am experiencing starting problems on a Jag 3.4 Mk2 auto when the engine is hot.
Car starts fine when cold and runs fine at speed but take it out on a run and park for 5 minutes or more and it won't start.
There is no ticking sound from the fuel pump so I presume that the fuel is still pressurized.
I've changed the fuel pump to a modern aftermarket electronic type, put in a new coil and new points thinking the problem was electrical but still to no avail.
Opening the bonnet and letting the engine cool for 10 minutes or so sometimes seems to do the trick (fuel vapourization perhaps?)
It also wants to cut out if it's idling in traffic for a sustained period which means having to rev the engine and slamming it into drive to keep it running, making sure not to rear end the car in front!
Depending on the car's mood it will start on what sounds like 2-3 cylinders and then suddenly,magically run normally!
The car was restored about 5 years ago and has only recently started it's tantrums.
Any suggestions or help would be greatfully appreciated as I'm becoming paranoid about taking it anywhere.

Re: Help Jag Mk2 hot engine starting problems

Hello Derek,
my thought was the coil, due to its location, but you have covered that, a new condenser is worth fitting though. I suggest that you go through the carburettor settings, idle mixture, synchronisation. It would seem that it is not flooding as the pump is silent. Ensure that the pistons and suction covers are clean inside (use only solvent, no abrasive of any sort) and that the jets are centered.
I presume you can see petrol in the little bowl on the inner wing?. You could try slackening the outlet of that bowl to see if petrol flows?

Alec

Re: Help Jag Mk2 hot engine starting problems

I had the exact same problem with an E Type. I also changed the coil only to find, after a great many trials and errors, that the new coil was also bad. Put in a cheapo NAPA coil and the car has been perfect.

Bruce

Re: Help Jag Mk2 hot engine starting problems

It sounds to me like a very specific carburettor problem. Here's what happens. As the engine and engine compartment get hot, the engine components get hot as well and that is not always a good thing. When gas gets hot, it expands a great deal (and that's a good thing... principles of internal combustion and whatnot). Now, your carb stores a bit of fuel so it has a steady supply while you're driving down the road. That's what the float bowl(s) are for. However, since you're storing that fuel in the engine compartment now and not the much cooler fuel tank, it is going to expand and create pressure in the float bowl. If it creates enough pressure, it forces it's way into the carburettor whether it should be there or not. What happens is basically the carburettor FLOODS itself out. That's why you don't have the problem at RPM, because you're consuming the gas before it has time to expand and run over. Same thing when you park it and come back. While it has sat there, the fuel has expanded tremendously and forced it's way into the carb/manifold. Airing the car out allows some of the excess fuel to dissipate just as you would do if you had pumped the gas peddle to much and flooded it that way. NOW, solutions for your problem. It may be a problem you can correct by adjusting your floats. If you have slightly less gas in the float bowl, it will have more room to expand before it forces through into the carb. Otherwise, there may be some sort of metering valve that is supposed to keep the fuel in the bowls when you are not pressing the gas peddle (You didn't mention what type of carbs you have on your Jag). This is where I would start as it is generally the culprit. Cheers!

Re: Help Jag Mk2 hot engine starting problems

Hello Lsp,
the 3.4 Jaguar MK 2 has HD6 S.U. carburettors and these have a vent pipe on each fuel bowl so cannot pressurise and should the float needle fail to shut off then excess petrol drains out of these vents.

Alec

P.S. I note your little rider at the bottom of your post, you cannot be a true beer drinker.