On my 83 H/O that I just installed a newly rebuilt 350 engine with a Performer aluminum manifold the manifold is getting very hot around the carb base due to the crossover port for the egr valve and the choke manifold on the other side of the base. After I have run the car up to temp and then let it set awile I have to crank on it quite a while before it will refire. I am thing that the manifold is getting hot enough that it is evaporating the fuel out of the carb. Any ideas how to keep this from happening. I am not running an egr valve. Thanks Larry

 

Try a phenolic spacer.

 

Once again, before spending a dime on anything, try a little no-cost troubleshooting. First, when you swapped the 350, did you retain the CCC or not? If you did, was it richened for the larger displacement? If you didn't keep it, what carb are you running?

Did you keep the 307 exhaust manifolds or not? If you did, is the EFE valve on the driver's side outlet functioning properly? If it's not fully open, it will force more exhaust flow through the crossover.

If all that is working, check the float level in the carb before and after hot soak. If you have a Qjet, this is easy. You can gauge float level be measuring through the bowl vent, as shown below. While the photo shows a ruler, you only care about the relative measurement before and after hot soak, so any lightweight strip of wood or plastic will work. Let it rest on top of the float and mark a line at the top of the vent tube. Try it again after hot soak and see if the mark is now lower in the tube. If not, you do NOT have a fuel boiling problem.

I'll point out that there are millions of Olds 350 motors on the road that don't require phenolic spacers, so maybe you should figure out what your real problem is rather than applying a bandaid.

 

I didn't keep anything from the 307 other than the edelbrock performer manifold and the exhaust manifolds. The valve in the exhaust wasn't reinstalled. Car has true duals with just the mufflers. Has no egr valve but does have the provision if needed. The carb is from a 77 350 olds and is a quadrajet. It has been rebuilt. I was having this same problem with the 307 when it was in the car and it was with a different quadrajet. Just seems like the manifold is hotter than it should be. What is this spacer that was referred to. I remember years ago we used a stainless plate under the carb. Would that help? Have thought about blocking the crossover if possible.

 

I had the passages blocked wth the Edelbrock plugs. (may have been part of manifold package) Helped tremondously in keeping the heat away from carb base ( E Performer RPM manifold) Evidence on manifold of previous carb (Edelbrock) boiling fuel out of bowls and staining/burning on crossover passage.
Changed to small Holley due to idle circuits not operating properly.
Plugs must be placed in solidly!!!! They can loosen due to expansion and rattle. (Ask me how I know).
No more heat problem with new setup.

Had used phenolic spacer to cut down on heat transfer.