Vapour Lock?

[Addy]

Ok more trouble from my lil viva hc. I've recently fitted an 1800 with all the running gear. from a magnum bought from sid, "Hey sid". It starts and runs forever but once you turn it off you cant start it up again for good long while.

I 've check that theres fuel coming through and i've got fire.
I've tried putting the choke on and flooding the engine with petrol but the sparks show no sign that petrol is getting through when then should have been soaked. So that leaves the carb its a twin choke webber by the way.

So is ther anything more i can do i will change the carb if needed but i thought the wise people of the forum may have some advise.

Thanks, Adam

[Sid]

If you take the top off the air filter and look down the carb whilst pumping the throttle be hand you should see squirts of fuel
going into the venturi.
If you *can* see plenty of fuel then I doubt vapour locking is the problem, but if you can't see any fuel squirting in then indeed
it must be boiling away from the float bowl. This is in fact the problem I get on my V6, which is also a sod to start when hot.

I wouldn't place too much significance in the plugs being "dry" when you take them out of a warm engine though, as and fuel on them
will evaporate quickly when they're hot.

Another thing you should check is that there is definitely a spark when hot starting. On some cars I've known the spark become very
weak when cranking on the starter, sometimes too weak to jump the plug gap under cylinder compression. You can determine this either
with an inline spark checker (a transparent device that fits between a lead and a plug) or using a timing light. If the timing light
doesnt flash regularly during cranking then there is no spark at the plug.

Yet another thing to check is that the valve clearances are OK when hot. If any of the valves aren't closing properly due to
insufficient tappet clearance then that would cause loss of compression when hot. I doubt that's the problem but worth checking
anyway.

I suspect the hot start problem on that engine IS fueling related. As I recall, with the stromberg it was terrible to start when
cold but fine when hot. With the weber it seems to be the opposite so I think either the fuel is boiling away OR conversely its too
rich. The carb came off a Cortina, which for some reason do seem to need a much richer mix than the magnum (as I discovered when I
fitted an 1800 Magnum carb to a Ford engine and it ran far too lean). It could be it needs smaller jets or a lower float level to
work right on the Magnum.
On the other hand, if its fuel vapourisation that's the problem then it might just need a thicker heat-spacer under the carb.

Sid

[pbottomley]

another thing to mention might be the fuel Lines? They run up the other side of the car on a slant four engine, and if these lines are still on the passanger side then they are too close to the exhaust manifold? Might vapourise the fule in the lines when tha car is stood still with no air flow.

A long shot I know but worth a look

[Addy]

Yeah i moved the fuel line over when i fitted the engine so that should be ok, but it was something i thought about. I also did as sid said and checked that there was fuel coming into the carb when it was hot, and it did.

There is a spark at the plugs when its hot but it may not be sufficient. I also checked the compression when it was cold and hot and they seems ok all where about 140 psi when cold and above this when hot. I'll try it again and make a few of the changes or test that you suggested and see how it goes.

Cheers, Adam