Anybody having problems with Vapor Lock?

Larry
Did that get it low enough to gravity feed?

 

Thats some interesting info cray1801. All the hot air making a convextion oven. I may use some aluminum sheet and try some kind of baffel attached to air cleaner base. Also will have to plumb dual snorkle to tbe front area. I already use a baseplate heatshield under the carb.

 

I have a mallory pump in tbe trunk. No pusher. But its a return system. Im thinking its not the safest in the trunk. But it works perfectly. I use a big fram can fuel filter in front of pump. With the key on you can ooen the gas cap and hear it draining back to the tank.

 

Added a heat shield under the carb., re-routed the fuel lines behind the carb....tried it, still no solution. Then I found some Ethanol Free 93 octane!

 

If you still have the normal steel fuel line from the pump to the carb, insulating it will help keep the fuel from boiling inside. I got a fiberglass insulating sleeve for it, and wrapped it with vinyl non-adhesive wire harness wrap. I've had zero vapor lock issues, even on hot days in the drive thru line.

 

Vapor lock doesn't usually happen in the plumbing from engine-driven pump to the carb. Fuel under pressure has a higher boiling point than the fuel being "sucked" from the tank to the fuel pump. Vapor lock is on the supply side of the pump, not the pressure side. IF the pressure side vaporized, the carb would flood. When the supply side vapor-locks, the engine-driven pump starves, so the engine goes lean and stalls.

If you're going to insulate fuel tubing, do it on the suction side of the pump.

If I were having vapor lock problems--and I'm not--the first thing I'd do is to assure that the tank is venting properly. Any vacuum in the tank due to plugged vent(s) reduces the boiling point of the fuel.

Same for any restriction in the fuel tube from tank-to-pump. Restrictions (kinked tubing, swollen hoses) cause problems. Side note: Don't confuse heat-related "vapor lock" with an air leak into the suction side of the pump perhaps due to aged 'n' degraded rubber fuel hose, or a rust pin-hole in the metal fuel tubing. Similarly, don't confuse an overly-hot carburetor that results in fuel boiling in the float bowl, with "vapor lock".

THEN, I'd make sure there was a vapor return fitting on the pump, with the usual small-diameter plumbing back to the tank.

I'd assure that the engine wasn't running much beyond the thermostat rating at idle or cruise. No need to have the radiator and engine hotter than necessary; blowing hot air onto; and conducting/radiating heat into the pump (and plumbing.)

AFTER all the above was proven satisfactory, and if there was still vapor lock, I'd cram an electric "pusher" pump back by the tank, with a pressure regulator somewhere near the carb/throttle body, scrapping the engine-driven pump entirely. Again, pressurized fuel has a higher boiling point than fuel under "suction".

 

Great inputs guys.

Vapor lock can happen even with the mentioned improvements, I know mine did.

Here's another contributor that can cause vapor lock, electric fans. Take a heat soaked car (15-30 min.) on a 85+ deg. day, sometimes it would start. When it did, the electric fans will come on right away, blowing hot air directly at the carb. Within a mile or a minute the engine would often die. Measurements of external bowl temperatures before and after confirmed it. I could always tell... if the front bowl was hot to the touch (120 deg. F or more) it would either not start or die within a mile after driving.

This is with 10% Ethanol 93 octane fuel in NC. Another issue for NC is that the summer and winter blends have the same Reid vapor pressure (RVP of 7.0)...

I use to carry some water and a rag with me on those hot days. A wet rag on the front bowls would reduce my wait times to re-start from ~45 min. to ~10 min.

 

Once again, gasoline boiling in the float bowls IS NOT VAPOR LOCK.

Vapor lock is when the fuel pump sucks vapor instead of liquid gasoline.

Either one can cause the engine to not run, or to not start. The cause is more-or-less the same thing--overheated fuel turning to vapor.

When it happens in the carb, first the engine gets flooded with fuel vapor and even some liquid fuel being pushed-out as some of the fuel expands into vapor. The engine will be too rich to run; and if the vaporized gasoline isn't replaced with liquid gasoline, eventually it's too lean to run.

When it happens at the fuel pump, the engine is too lean to run--the pump can't pump vapor very efficiently. As far as the fuel pump is concerned, the vehicle fuel tank might as well be "out of gas".