No need to ch manifolds. Lets see if we can solve it as is. heat riser sending heat up top?. Need a thin gasket on either side of the 1/2 black plastic phenolic spacer? E10 gas (ethanol) by chance. the eddy 750 may have an issue . Something besides the cast iron is causing the prob & if it is not heat related check for a good blue spark when hot

When E10 became an option at the pumps here in Nebraska in the early 80's it caused quite a bit of vapor locking and stalling at stoplights in the summertime but then later w the intro of fuel injection and carbs becoming nearly extinct it became a non issue. Some eng setups are much more susceptible than others and the ones that are it is severe and a real pain. Any way you could get the E10 all the way out & toss in several gallons of non alcohol fuel of some kind (maybe some racing gas ) to confirm or deny that that is the prob. Changing the intake is not the solution imnho

Putting an alum intake on (and in Florida) blocking the heat-crossover) will help big-time.

Eddy Performer RPM.

I love mine!

I think i'm going to swap out the manifold and look for a place that sells decent gas........ the vapor lock theory sounds familiar... i used to live in Tucson AZ and had a stock 67 383hp and drove it for about 3 yrs(before I wrecked it ) and I honestly opened the hood about a dozen times (too interested in the girls back then ).... they had regular leaded pump gas at every station and NEVER had a heating issue.

Holler w what ends up taking care of it

I would use the Edelbrock Performer RPM dual plane intake. The RPM intake blocks off the exhaust crossover so it should not get as hot as the intakes that use the exhaust crossover. Also, make sure the heat valve in the exhaust manifold is not sticking closed. That would cause you exhaust to flow through the intake crossover and out the drivers exhaust making the intake really hot.