I'm running twin 40's, previously listed and agreed ok. When my engine is hot (thermostat open) the engine struggles and dies.

I thought could be crap in tank / filter but have checked and replaced with no change.

As this happens only when hot could this be fuel evaporation due to manifolds being to hot on the head?

Yes, it could be.

Are you running the phenolic (sp?) spacers/insulators between the intake manifolds and the heads?
They are important in keeping the manifolds (and carbs) cooler.

Also a good idea to utilize the return line to the tank to keep the gasoline moving. A lot of people plug it when they convert to carbs but moving fuel is less likely to boil in the float bowls.

I have the manifold fitted to head with only a gasket.

A quick search shows up spacers from 3 to 9mm. What should I be looking at? Too far and that may cause linkage issues on the csp bellcrank linkage.

No return so I may get a knock on from the bowls but I'll rule out one thing at a time.

These are an example

https://www.dellorto.co.uk/shop/weber-carbu...nsulator-plate/

The phenolic spacers are the ones that came stock on our engines with the fuel injection and insulate the runners from the heads.

Last i checked (it's been a few years) they were still readily available from all the usual sources.

I used them on my carbed 2056 and it made a big difference ...

They look like this and go between the head and the bottom of the intake runners, they are several mm thick:

PS: I used a thin film of sealant on both sides, not sure if that is needed but it seemed like a good idea at the time

after having properly driven the car the other day on a 6 mile loop i just about limped back onto the drive.

i have the spacers fitted at the bottom of the manifolds but i think it's not enough and i still have the same problem.

the car runs like a dream when cold and warming up but the driven heat seems too much.

i'm going to fit a return pipe back to the tank and hopefully that will cure the issue.

now i need to look at how to fit (in a tidy way) the return pipes in the engine bay.

Also how old is your coil? it was discussed in another thread with the same symptoms...

the coil was new with the distributor about a year ago. i touched it to see if it overheated but wasn't very hot.

It seems to me that your jetting might be a bit off. All my Type-4s with carbs coughed , sputtered and spit when warming up then ran like champ one at temperature.

I am no carb expert to let you know. But your symptoms seem odd to me. That is why the -6 has a hand throttle to let them warm up.

Ignition is a possibility check you plug heat range as I got the parts counter guy slipped me the wrong ones once and it cost me a head.