Does anyone out there know if vapor lock is a common problem with 396 big block engines?
I have a 1968 ss-396 325 h.p. Chevelle with a Q-jet carb. The engine runs just fine when the outside temperature is below 90 degrees F. When the outside temperature rises above 95 degrees F. and I do stop and go traffic the engine seems to want to stall out and misfire (vapor lock). If my car is vapor locking, is it vapor locking in the carb. or fuel line? Will a carburetor lift spacer help? Any suggestions would be greatly appreciated.

------------------
1968 Chevelle SS-396 Convertible

When the temperature goes up and affects the engines performance three things come to mind.

One...coil issues. A coil that is old and fried will usually work okay when cool, but give it some heat and it will/can misfire or completely leave you hangin! Check this by getting your engine to the point of misfiring and then lay an ice riddled rag over the coil and see what happens. If it continues move to number two..or you can simply change it out if you are in the mind to.

Two, usually fuel boiling (not vapor lock) will cause all kinds of misfirings when heat is present. This is the fuel actually boiling away in the bowls. Protection can be insulated fuel lines from the pump to the carb and a plastic spacer. These plastic spacers work better than the metal shields. Conduction far outperforms convection and radiation any day! So, make sure that you get a spacer appropriate for your intake. Single plains are open spacers and duals are holed.

Third, vapor lock is a condition that usually shuts your engine down completely...not just misfiring. The fuel line to the pump gets hot and boils fuel in the line and then you have a gassified trap that is in line and when arriving at the pump cannot be cleared without cooling and condensing usually. If your engine is simply missing....then this is not the culprit in my opinion even tho insulating the lines with split rubber fuel hoses on top of the metal lines is a good idea anyway.



------------------
Steve Jack - ConceptOne Pulleys and Brackets / Engineering & Marketing Technologies

To answer your basic question lumberman the big blocks did not suffer from vapor lock as a normal thing. Perhaps you might examine your cooling system more closely and see if there are any deficiencies. JMHO.

It sounds like I am having the same problem...go to the heating and cooling forum and look back about 10 days under the heading, sputtering motor when hot. I had a few replies that may also help your situation. If I fix my problem I'll let you know. If you seem to get yours fixed, let me know.

Craig

Thanks for the suggestions! I think I will try a new coil and a plastic carburetor spacer first. It sure feels like I am temporarily running out of gas and trying to stall out. I think it might be the fuel boiling situation that HOTRODSRJ described.