Hot Fuel Pump

[archigator]

I've read on this forum that an Elan that runs well when cold, and then sputters once the engine heats up to normal operating temperature, can sometimes be attributed to a faulty mechanical fuel pump. (Also told it could be a faulty coil.) But when I contact a mechanical fuel pump rebuilder of some repute (Antique Auto Parts Cellar), he tells me that if a mechanical fuel pump is malfunctioning, it will malfunction when cold as well as when hot.

What is it that would make a mechanical fuel pump malfunction when hot, yet operate normally at cold start-up?
Or is this, in fact, not the case?

Thanks,

Gary
'71 Sprint FHC
Miami, Florida

[rgh0]

A mechanical pump located near the engine can vapor lock when it gets hot and fail to prime with fuel and thus stop pumping. Rarely a problem on the Elan compared to some other cars though

cheers
Rohan

[oldelanman]

A mechanical pump located near the engine can vapor lock when it gets hot and fail to prime with fuel and thus stop pumping. Rarely a problem on the Elan compared to some other cars though

cheers
Rohan

Isn't this why there is a 1/4" thick plastic spacer fitted between the pump and the engine block to reduce the heat transfer ?


Regards,

[archigator]

Isn't this why there is a 1/4" thick plastic spacer fitted between the pump and the engine block to reduce the heat transfer ?

When I received my rebuilt fuel pump back recently, it was sent back with all of the old parts that had been replaced... along with a new paper gasket for mounting to the engine, which I assume is the standard installation for many cars. I would guess that since the AC mechanical pump is a standard unit, not exclusive to Lotus cars only, the composite spacer on the Elan is used to correctly locate the pump's lever arm over the internal jackshaft on a compact engine. This, I would guess, has the added benefit of reduced heat transfer as well as some minor vibration isolation to reduce fuel frothing.

I guess the question I'm trying to resolve is: "Is there anything in the internal workings of the mechanical fuel pump that would cause the pump to operate sufficiently when the engine is cold, but not work properly once the engine has come up to temperature?" It was noted elsewhere in the forum that this could be the "sign of a failing pump," but I don't know that that is the case. Is this a symptom of a failing pump diaphragm? The fuel pump rebuilder tells me "no." He says that a failing pump is a failing pump, with the same symptoms at all temperatures. Does anyone know anything to the contrary?

Thanks,

Gary
'71 Sprint FHC
Miami, Florida

[robertverhey]

Can't see how temperature would affect the trusty old AC mechanical fuel pump, but I did have vapor lock issues in a lotus cortina once, during a particularly hot spell, only cured eventually by fitting an electric "push" pump in the boot to get that fuel moving along the line.

Electrical problems can be heat related too, things like a marginal distributor pigtail lead, which may break down after it gets hot, and other leads in the low tension circuit. Then there's the ht circuit, plugs and ht leads, coil, which you've already mentioned.

Back to the fuel system, there's the carburetor float levels, jets and filters to check. Hours of diagnostic fun!

Robert