Dear friends
This weekend I drove it again! It is such a wonderful car, I made some 200 +
kilometers. Once I got the problem again, that the car doesn’t run on all
cylinders. I cleaned the sparking plugs, and ewverything went normal since then.
But there is another problem. On certain temperature - not too hot, but also not
too cold, when trying to start the car. It starts but doesn’t keep running. When
trying to keep the car running in depressing the gas pedal, it starts misfiring,
that all the dogs in the neighboorhood start whining. Anyhow I try, it misfires
and stops after a while. When I leave the car for some minutes, and then Itry
again it normally starts without any problem!
What’s the clue to this mystery?
I have noticed that there is some gas leaking from the auxillary starting
carburettor. Is its thermostat broken, or is it malfunctioning? (When cold and
when very hot it starts without problems).
A friend of mine had the idea that there were may be air bobbles in the fuel,
because of thermical expansion and retraction of the fuel, which could cause
this misfiring.
Any hints or ideas?
B.t.w. I made my first pass in the swiss mountains, about 1000 m high.
Everything was marvellous.
Best regards Zoran Mitrovic
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But there is another problem. On certain temperature - not too hot, but
also not
too cold, when trying to start the car. It starts but doesn’t keep
running. When
trying to keep the car running in depressing the gas pedal, it starts
misfiring,
that all the dogs in the neighboorhood start whining. Anyhow I try, it misfires
and stops after a while. When I leave the car for some minutes, and then I try
again it normally starts without any problem!
What’s the clue to this mystery?
Best regards Zoran Mitrovic
It could be the choke. If yours has the thermostatic choke, I understand it
can cut off before the engine gets as warm as it likes. Mine ( with a
bypass switch to the choke) runs rough and tends to die when somewhat warm
(50-70C) but clears up once the temp gets above 80C. Like me, it is also
slow to get up and going when cold.
Regards,
Jim Voorhies
XK140 FHC
All xk120s seem to have the reputation of difficult starting when hot. I finally got fed up with this inconvenience and after looking at the discussion i made two modifications which have eradicated the problem. Firstly i moved the coil to the inside fender , and secondly and more significantly put a switch in the fuel pump supply circuit. After a decent run before i switch the ignition off i let the car run for about 20 seconds with the fuel pump switch off. This seems to have cured the problem.
I believe it is a fuel vaporisation issue rather than an overheated coil but i made both modifications to make sure, Brian Kay
Welcome Brian.
Yes, the coil under the intake manifold was probably Lyons’ idea for a clean appearance; I burned my arm trying to change it one miserable night.
Do your carbs get really hot a few minutes after shutting off, like you can’t touch them, hot as the intake manifold?
Mine did, and this causes the fuel in the jets to vaporize too low, causing a lean condition, hard to start.
The factory cure is 1/4" thick spacers between the carbs and intake manifold. The factory did this on all XK engines beginning in 1952.
This is what I did, and it was cured immediately, the carbs are not as hot as the manifold any more.
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seeing the thread now…re the old old posts…a fuel pump electical kill switch is a good idea for several uses…(testing other electric componants with power…but not fuel pump, and drive off theft), but NOT for the use stated : to solve the fuel heat vapor issue. Running the engine with fuel pump off is like running out of gas…the engine will run very lean for a time as it is fuel starved, and that lean even for a short time can be harmful. Some motorcycle guys do it to empty the carb before shut off…by closing the fuel supply lever…the engine pops and pops as it stalls out…not good. Also…a heat shield thermo wrap on the coil can help…but looks goofy. My dad made an air duct to the carbs from out of a few canned peaches cans to prevent vapor lock on our old Studebaker on a road trip…we all had to eat two cans of peaches…And…the cold start carb, in combination with the coolant thermostat, is there for a reason…it does take a while to bring that big block up to designed operating temp of mid 70s C.
Nick
Hi Nick
Not sure my reply reached you.
I may not have made clear the purpose of my modification. The idea is not to switch off the fuel pump until the engine stops.
The procedure is to switch off fuel supply for a short interval before we stop the engine. I usually wait about 15 seconds. The result is that when the engine is stopped with no airflow and under bonnet temperatures rise, there is much less fuel in the system so the overpressure and vaporization does not occur. This is working well for me and the engine now starts quickly after a stop in hot conditions.
I did also move my coil to a cooler position but I am sure that the fuel issue is the overriding cause of the problems.
Brian
