240Z Dual Weber 32/36 Carbs: Problems starting when warm

[lm71z]

Question for those with experience with these carbs. The car is a 1971 Datsun 240Z with dual Weber 32/36 carbs. It starts and runs perfectly from a cold start. Plenty of power, no issues while driving. However, if it sits for 5-10 minutes, it will take several cranks to fire back up and will often smell of gas and/or smoke out the back. I assume that fuel vapor or fuel is continuing to make its way into the manifold after the car has been warmed up and then shut off. The only time it starts up perfectly is if it sits for 1-2 days (I assume this is because the extra fuel from the carbs has evaporated?)

 

We have replaced the accelerator pumps, needle and seats, and power valves.

Any idea what the fix could be? Any ideas for a solution would be appreciated.

[Patcon]

My first thought would be to check float levels

[Captain Obvious]

Sounds like textbook fuel percolation.

[lm71z]

Okay, I also forgot to mention it has unwrapped headers. Was thinking the heat from those could possibly be causing the gas on the float bowls to evaporate and expand. I’m going to test this by only driving it for a mile or less, then turning it off for 5 min and see if I have the same restart issue when it’s not warmed up. For float level, should I consider lowering that? Seems to me that the only 2 causes could be the fuel evaporating from heat and/or improper float levels? Is there anything else I’m missing?

[Mark Maras]

 Do you have a heat shield under the carbs?

[lm71z]

Nope, in the process of trying to find one, but it seems like I’ll have to have one made.

[Zed Head]

 

[Mark Maras]

 Ztherapy sells heat shields for $100.00, no core. They list one part # but I believe there were three (somewhat) different heat shields over the years. 

[Patcon]

I would start with the heat shield and heat issues before I looked at the float levels

[lm71z]

Okay, we actually have a factory heat shield under these, but it's the SU Carb heat shield and it looks like it doesnt block all of the heat from the header

Edited September 23, 2018 by lm71z

[Mark Maras]

To confirm that fuel percolation is the problem, next time you shut it down when it's warm. crack the hood and let some heat out from the engine bay. Then see if it starts easier.