Re: Posible vapor lock solution?

Posted by Tim Cole On 2012/6/29 17:39:59

These cases of verifiable vapor lock are really interesting.

Obviously the Packard company was able produce problems at the proving grounds because they started putting heat shields around the fuel pump and carburetor.

That one about the filter bowl has me scratching my head because if the motor is starving for fuel then there should be no pressure in the line unless the float is stuck closed. Perhaps the water splashing on the fuel pump released a stuck valve.

Packard cited vapor lock as a cause of poor performance but said nothing further about how to service the problem except for updraft carburetors where they said vapor locking occurs in an idling motor.

One of my suspicions is that there is simply a problem with these old fuel pumps. Maybe the valves don't work right because the castings are getting old and creating problems. They are after all just cheap zinc pot metal. Years ago people were putting electric fuel pumps on cars because they couldn't get parts for the mechanical pump. I remember one Caddy 12 that had the fuel pump gutted and was running on one of those fantastic Stewart-Warner electric pumps. It never broke down so maybe these cars should just be running all electric with a dummy mechanical pump.

Suppose for example that the pump is creating suction internally because of the valves. This reduced pressure will cause gas to boil.

Another possibility is that a restriction in the supply line is causing a low side vacuum. Once I dealt with a Clipper that acted like vapor lock. You could turn the electric pump on and the thing would still be starving for gas at full throttle. The location was terrible so I redid the whole thing and put a Hirsch Airtex unit midway in the line at the lowest point. That fixed it.

The postwar cars are designed to create a syphon action that keeps the fuel pump full when parked. If a filter or fuel pump is higher than the lowest point in the fuel line then that could create a low pressure point where gas boils.