Fuel vapourisation

[David Morris]

Hi there,

I have mentioned this problem in JowettTalk before, but it is still giving us serious problems.

Perhaps I should explain. Our Javelin carb problems are really strange. When we are running, the carbs are totally normal. The engine tick over is correct and she does not really overheat ( thank goodness ). The problems only occur when the car is left with the engine switched off and the engine is hot. If we leave the car for, say 5 mins, when getting petrol for instance, the car will re-start promptly and completely normally. However, leave the hot car for 30 mins and you might as well walk away - there will be no chance of it starting for at least another hour.

It may not even be the carbs at all, but fuel vapourisation somewhere in the fuel line. When the engine is in this mood, I have tried taking off the carb bowls, which are still full of fuel, and with the manual pump lever, pumping through some more fuel, all to no avail. I have since fitted an electric fuel pump, which is much better when starting but has unfortunately had no effect on this hot starting situation. When the engine is hot there is still a good spark, so I am at a loss to explain it.

Chris Coles has suggested heat deflector plates under each carb, shiny underneath and black on top, which may well be a good solution. However, any other suggestions for a cause and preferably a cure would be really welcome.

I suspect our UK recipe for unleaded petrol has a lot to do with this problem, but in that case it seems strange that other people haven't had the same difficulties?

As it is, I think we are having to look for some extended stops on our way up to Crieff, to allow everything to cool off.

All the best,

David

[Keith Andrews]

Are u sure it is fuel?
Next time it happens, squirt some ether CRC engine start in the carb.
If it fires...fuel if not electrical

Check that u have a 13v coil on 12v system generally they have a 6 or 12 stamped on the bottom.

Starter motor, could be dry solder joints between the part wher the brushes run and the armeture coils...when hot these can draw too much power and not enough let to give a good spark...

Dropped a spark plug on the ground? may have a fine crk that opens with heat...Drop a plug, throw it away, replace.

I dont kjnow it javelins have a insulation block/spacer between manifold and carb...?? most older cars did to stop transfer of heat.

A note on heat shelds...they are not so much a heat sheld but a heat sink
Heat travels to the coldest piont, older cars had metal shelds...usually painted with a thin layer matt black. Instead of the heat moving up to the carb, it gets distracted and moves to the outside edges of the sheld...
Aluminium has far greater heat transfer properties than seet metal, and a matt black surface can increase heat disapation 40 to 60% over a shiney surface.

Try the CRC either engine start.

[Forumadmin]

I would suspect a rich mixture caused by flooding carbs. This might be worse if left on hill nose down as needle valves may be leaking.

May even be ignition timing too advanced or blocked air filter. Presumably you tried to start with bonnet open! Ignition timing problem might be caused by weak springs on weights. Check ignition timing with strobe, as static may be ok, but as soon as engine turns, timing advances.

I had a similar problem and it was the coil getting hot. But then that also stopped the car in transit. Also capacitor might suffer from heat. Quickest way is fit a complete new distributor.

[vicboddy]

I almost feel embarassed to suggest this but here goes: I had a somewhat similar problem recently on an XK Jag. It would start and run well on trips, but as soon as I had to slow down in towns for any significant period, the engine would cut out and not restart until it had cooled down. This turned out to be fault in a (new) rotor arm which tracked to earth when hot. And everytime this happened I would have the cap off the distributer, and of course it cooled down and thenran again.

RgdS vic

[David Morris]

Hi there,

Just before we set off for the NJD Rally at Crieff, I had an e-mail from Simon Pointon. He had the same problem with his Jupiter and had solved it by fitting a new coil.

It was down to our local car parts shop for me and I fitted a new coil just before we left. Result? The problem has been completely cured!

Previously, when we had the problem, I had tried for a spark and convinced myself that all was well - just shows how wrong you can be!

Many thanks Simon! We did 1240 miles there and back and she started every time 'on the button', even when really hot.

By the way - what a super Rally we had at Crieff? How did the Scots arrange such wonderful weather? A big thank you to all involved.

All the best,

David

[Keith Andrews]

There is an old school saying
"There is many a carb tuned by changing spark plugs"