Hot starting problem with Series 2A petrol

I have been having hot starting problems with my 1969 S2a for several years now and having replaced everything I can think of its still happening. The only cure seems to be to lift the bonnet and wait for it to cool down then it starts again. The engine doesn't overheat and when it starts it runs fine till you stop again. Last year I traced a fault to a high resistance in the cable going to the ignition switch and had to replace the switch as contacts were scorched and this seemed to greatly improve starting but its all back again and the switch contcats are OK. Have replaced the coil, carburator, condenser etc. What am I missing??

Does the engine spin over but not fire? If so then I think that it is a fuel evaporation problem. If the engine is sluggish to spin over then I would think that it could be a heat related electrical resistance problem in the starter motor. Using a jump lead from battery earth to the starter motor body will help eleminate earthing problems.

Often a hot starting problem is caused by a FLOAT CHAMBER fuel level set TOO HIGH.

While the engine is running the fuel is always being replaced, and stays relatively cool, but as soon as you stop with a HOT engine the fuel stops flowing, then heats up and expands, and pours over the edge into the manifold. Engine flooded on the spot. If your float needle valve is the least bit leaky that will make it worse as the spring-loaded lift pump will empty itself into the carb float chamber and flood it.

Also, is there a plastic spacer between carb and manifold? Some setups use one specially to slow down the heat transfer into the carb body.

Stage One for you is probably to set the float level right or a tiny bit LOW.

CharlesY

Very interesting. Its a new Webber carb fitted last year but the last time it stopped I noticed that the inline fuel filter was empty. I eventually managed to fill it using the manual lever on the fuel pump and it started shortly after that. Ill check the spacer as well. Very many thanks
Donnie, Western Isles

Donnieit said:

Very interesting. Its a new Webber carb fitted last year but the last time it stopped I noticed that the inline fuel filter was empty. I eventually managed to fill it using the manual lever on the fuel pump and it started shortly after that. Ill check the spacer as well. Very many thanks
Donnie, Western Isles

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That sounds like some good clues to me.
The inline filter should probably stay filled.
The hand-priming lever should hoick fuel up smartish (unless the INNER pump lever is sitting on the cam). It should not be "eventually".
And then it started ... in other words, when the fuel reached the carb, it started?

If the check-valves in the lift pump are a bit leaky the fuel may drain back all the way to the tank and that will delay starting-up till the system is filled again. I think it may be time to take the lift pump off and have a good look at it. The check-valves should be on both inlet and outlet, and they should both allow fuel to pass ONLY towards the carb. But perhaps the pump is knackered and on its way out? It doesn't sound like the pump is a good 'un to me.

SO much to go wrong, and to try to work out!

After fifty years of practice one becomes quite good at guessing!

CharlesY

CharlesY said:

That sounds like some good clues to me.
The inline filter should probably stay filled.
The hand-priming lever should hoick fuel up smartish (unless the INNER pump lever is sitting on the cam). It should not be "eventually".
And then it started ... in other words, when the fuel reached the carb, it started?

If the check-valves in the lift pump are a bit leaky the fuel may drain back all the way to the tank and that will delay starting-up till the system is filled again. I think it may be time to take the lift pump off and have a good look at it. The check-valves should be on both inlet and outlet, and they should both allow fuel to pass ONLY towards the carb. But perhaps the pump is knackered and on its way out? It doesn't sound like the pump is a good 'un to me.

SO much to go wrong, and to try to work out!

After fifty years of practice one becomes quite good at guessing!

CharlesY

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Had the fuel pump replaced 3 years ago but the hand priming lever was delivering very little to the inline filter so will check that as well. The glass bowl was full though so this suggests it didn't drain back to the tank. If I purchase a kit for the fuel pump will it include check-valves?
Donnie

Donnieit said:

Had the fuel pump replaced 3 years ago but the hand priming lever was delivering very little to the inline filter so will check that as well. The glass bowl was full though so this suggests it didn't drain back to the tank. If I purchase a kit for the fuel pump will it include check-valves?
Donnie

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The pump will NOT hand-prime well if the INNER lever is sitting on the cam.
You will have to learn what this feels like.
You may need to turn the engine about a quarter turn to get the pump lever off the cam inside.

NEVER try to turn the engine by the fanblades unless the keys are in you pocket! Ace way to lose some fingers that is.

CharlesY