1972 Porsche won’t start when engine is hot - open to any suggestions

[911T1972]

I have a 1972 Porsche with a 2.7 L. engine with Zenith TIN 40 carburetors. It starts well when the engine is cold and runs great, but it will not start when the engine is hot. The starter turns the engine over with good rotations. Operating temperature is usually around 190 to 210 degrees reading from the oil temperature gauge. I checked the oil temperature with another thermometer and the dash oil temperature gauge is accurate. I have to let the engine cool down for about 30 minutes, then it will start again. I’m open to any suggestions anyone might have.
Thanks,
Chris

[70SWT]

This is reaching back a bit in the memory, but I believe you could be experiencing heat soak resulting in vapor lock. You need to use phenolic spacers to reduce heat transfer from the case into the induction system.

Also, Grady Clay advised me on this way back once when I was having fuel boil-over in one Weber. I believe he recommended making the fuel system a return loop rather than the dead-end type. This would allow recirculating cooling of the fuel.

I have also heard of guys using creative heat-reduction strategies such as wraps and shields to reduce radiant heat soak, but I believe the bulk of it comes through conduction from direct contact.

[Grady Clay]

Here are some good links:

Weber fuel recirculation- Questions

fuel pump rpblem - vapor lock?

Early 911 Warm Start Problem

I need to see if I can find the original modified Factory diagram I posted so I can add the proper legends.

The best basic set-up is to have a circulating system with as few components in the engine compartment as possible. This has a flow-through Bosch pump (fuel flow cools the pump) on the front cross-member, the fuel filter and bypass-type pressure regulator up front. All the fuel hoses/pipes from the end of the tunnel to the carb inlets should be insulated.

I use two or three phenolic insulators between the heads and the intake manifolds.

Keep your fuel tank relatively full in hot weather.

Best,
Grady

[70SWT]

Grady, I figured you would come to the rescue for this gent...cheers, Al

[Quickstep192]

On my Webers, before the phenolic insulators were installed, the fuel would acutally boil in the bowls and percolate over the top into the throat making it hard or impossible to start. not to mention a bit scary.