Quote:
Originally Posted by JBanna
I have had the vapor lock issue on heavy acceleration in outdoor temps of 80+ and can't really figure it out - I have a Carter street pump set at 6 psi, but have kept the original fuel lines. My car is a 78 T/A with a 455 Pontiac, with 4x heads and a roller cam with moderate increases in duration and lift, so I still have good vacuum; I also switched to headers and full dual exhaust, an Edelbrock Performer manifold, and run a Rochester Quadrajet. I also had my distributor curved. Many people have doubted vapor lock, but the hesitation and faltering does not happen in cooler weather; in fact, I made a 100+ dash one spring at temps around 50 and had no issues, no matter how hard I mashed the accelerator. Finally, the closest my fuel lines get to the headers is about 3 inches, and the thermostat is a 195 degree high flow model.
Any other ideas other than replacing fuel lines and/or fuel pump? How does one even confirm vapor lock?
Thanks, Joe
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Vapor lock is hard to confirm since you cant really see the fuel in the lines or carb. True vapor lock is when the fuel is so hot it turns to vapor in the lines/carb, one way to check the fuel at the carb, is when it acts up pull over instantly & shut off the engine, pop the hood & pull air cleaner then look down the carb while operating the throttle, if you see raw fuel squirt out its probably not vapor lock, if its an intermittent broken spray of fuel or looks like an aerated mist then its likely related to overheated fuel. the other option is to use a fuel gauge plumbed to the windshield or like 81turbo said to get a gopro camera to view the gauge, if fuel psi drops from normal then its a fuel supply or vapor related issue.
Vapor lock is not as common as some think, until 81turbo investigated more he would have sworn it was vapor lock but turns out it was ignition related.... at this at this point. I have random fuel cut out issues at the drag strip on hard launches at low 11sec runs, based on the symptoms & that some times its hot summer days many people would say its vapor lock, but in my case its fuel supply related, have confirmed fuel is not evaporating in the carb on the hottest of days.
Big cube or high hp/rpm engines using stock lines or wimpy pumps can have fuel related symptoms in any temps, but heat can exaggerate that just like it can with electrical issues. Do some more testing to narrow it down & consider some heat wrap on the lines near super hot sources like headers.