Vapour lock??

D

dav118118

Club Member
hi,
I have a 260z with a 280 engine with twin hitachis from a 240Z and whilst using the car today after a hot run the idle seemed a little low and eventually stalled. When the car had cooled down it was ok again. It seems fine running the engine up to temp with the hood open so was thinking it may be a fuel vapourisation thing with the hot weather etc. I have the correct heat shield under the carbs too. When I blip the throttle when hot and at idle it’s fine and revs cleanly through.

I recently fitted a viscous fan to accompany the electric fan I have and I’m thinking the fan is pulling in additional heat from the rad into the engine bay which is causing the issue

Has anyone else experienced this and what have people done to prevent this from reoccurring?

Your thoughts are most welcome

Thanks, luke
 
Are you using the original airbox/filter setup too? What sort of exhaust manifold? I think a completely stock setup should be fine in this weather.
 
The cooling systems on these cars is normally pretty good, so unless your electric fan is particularly small you should'nt need the engine driven fan as well.

Is the return pipework to the tank clear? as this helps keep fuel a little bit cooler as it circulates around the system.
 
Yes a completely stock air box with air filter. The return filter is clear as I’ve blown down the pipe and all flexi pipes are new. Maybe I need to increase idle speed as it isles around 750rpm when warm? I reacon somewhere near 900 would be better or maybe wrap the fuel hoses etc as they were in the early cars?
 
By my calcs, the fuel lines hold very little fuel - I think not much to gain by insulating them.
Raising the idle can’t hurt, although 750 isn’t low.
What’s the idle mixture like? If it’s already quite rich, hot air might lower the idle.
(Or does hot air make it leaner ? [emoji849])
 
By the condition of the plugs I would say it’s running slightly on the rich side, which is how I would prefer it to run. Darkish brown on the electrode.
 
What type of fuel pump are you running. Sometimes it does get vapour lock when hot if just using a mech pump. I thought 260z also have an electric pump ( or was that just the 2+2?).
 
Ive got a facet red top pump located near the rear wheel arch. I have a pressure regulator set at 2 psi in the engine bay
 
These carbs like around 2.5 - 3 psi ideally, but will accept a bit more without problems, not sure if 2 psi would cause your issue when hot, but no harm in upping it a bit to see if it helps.

Ive got a facet silver top, which i think is 4 - 5 psi, i dont use a regulator and ive never suffered from vapourisation, i also have an electric fan.
 
I would just make sure any fuel filters are clear. I've had restricted fuel flow and after a 'rest' the car will start and 'blip' ok.

I wouldn't concern yourself with the second fan drawing hot air in, it will be cooling the engine bay. The engine will be warmer than the air.

My fuel lines are insulated on my blue car (built by Dave Jarman) so he must have thought it worthwhile. I think every little bit of cooling helps. I agree they don't hold much fuel but they will warm all the fuel passing through them.

Is the car running at the correct temp?

Jon asked what type of exhaust manifold you have, is it standard? If not you may benefit from a bigger heat shield.
 
dav118118 said:
Yes a completely stock air box with air filter. The return filter is clear as I’ve blown down the pipe and all flexi pipes are new. Maybe I need to increase idle speed as it isles around 750rpm when warm? I reacon somewhere near 900 would be better or maybe wrap the fuel hoses etc as they were in the early cars?
Click to expand...

What do you mean by - the return filter?

With your engine off and your pump running take the tank filler cap off, can you hear fuel returning to the tank?
 
Rob Gaskin said:
What do you mean by - the return filter?

With your engine off and your pump running take the tank filler cap off, can you hear fuel returning to the tank?
Click to expand...
Sorry, I didn’t mean return filter I meant return line. And yes I’ve already checked the return line is clear doing exactly what u said
 
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