Carburetor Fuel Percolation

[Kelvin]

Hello,
I've installed a 455 engine in an 84 Cutlass and have a problem with fuel percolation. Causing poor idling and hard start up. I've insulated fuel lines, wrapped exhaust headers, and installed an insulating spacer under the carb. Limited hood clearance restricted the spacer to 1/4 inch. These steps helped. But driving in Central Florida heat makes the problem worse. I've read that a bypass fuel regulator would help. Does anyone have experience with this? Can the fuel return line from the mechanical fuel pump be teed for the regulator bypass return line? I believe this would help with hot idle, but would this help with hot startup?

 

[565bbchevy]

installed an insulating spacer under the carb. Limited hood clearance restricted the spacer to 1/4 inch

What is your spacer made of?

 

[Kelvin]

What is your spacer made of?

nitrile rubber

 

[565bbchevy]

nitrile rubber

I have tried them all from plastic to stacked aluminum plates, wood spacers work well but are not strong or machinable, so I have been using Jomar phenolic spacers for years and they are the best IMO.

Phenolic Carburetor Spacers

Racers, street rodders, and anyone who wants to maximize an engine's performance, rely on JOMAR Phenolic Carburetor spacers. The advanced phenolic laminate transfers approximately ten times less heat to the carburetor resulting in cooler denser fuel/air mixtures. In addition, spacers are used to...

jomarperformance.com

 

[Kelvin]

I have tried them all from plastic to stacked aluminum plates, wood spacers work well but are not strong or machinable, so I have been using Jomar phenolic spacers for years and they are the best IMO.

Phenolic Carburetor Spacers

Racers, street rodders, and anyone who wants to maximize an engine's performance, rely on JOMAR Phenolic Carburetor spacers. The advanced phenolic laminate transfers approximately ten times less heat to the carburetor resulting in cooler denser fuel/air mixtures. In addition, spacers are used to...

jomarperformance.com

Thank you. I'm looking into any and all suggestions.

 

[spongbob]

Thank you. I'm looking into any and all suggestions.

Your in florida pull the intake and block the heat riser passages to both or 1 side between head and intake with thin sheetmetal .018...ect also you got a 455 theres half a chance you have a crack into bottom of the plenum into the heat riser passage that's what they did(455/394 ) I can tell you I replaced more then a couple used to get new intake for 45, new I bet you can't get one now fir that now".if you think it's cracked put tin sheetmetal on both sides yes on top of the intake gasket to cover both holes this will help a lot even with out new intake but looks like you going to need an intake gasket and say some ultra grey fir water jacket spots and two peices of flat sheet metal...do not use no1 permatex by any means no 2 is fine

 

[Bonnewagon]

This^^^

block the heat riser passages

No need for exhaust heat crossover in Florida. Some people fill it with molten aluminum, but a sheet metal blocker is EZPZ.