Re: Car won't start without priming carb

Posted by shinyhubcap On 2016/10/11 11:13:10

car wont start without "priming" cont:

Lets review the changes in chemistry of gasoline down thru the years to get a better understanding of why some cars wont start when they are hot.

If we go back to the early twenties, we will see your Packard had something called a "Fuelizer". It was nothing more than a spark plug in the intake manifold !

The fuel of that day had such a high boiling point, best way to get your car started on a cold morning was to start "lighting the fire" in the intake manifold.

How to make it easier to get cars started on a cold morning? Increase the Reid Vapor Pressure - i.e. make the fuel more volital.

The introduction of devices like the vacuum tank of the 1920's, and the "suction type" fuel pump in the early 1930's standardized fuel supply from the tank to the motor (with the exception of the Ford Model "A", which had the fuel tank above the engine, right behind the dashboard..!

The introduction of "suction style" fuel supply ( again...either the vaccum tanks of the 1920,s or the "suction style" fuel pumps that came out in '32, caused additional problems.

Because when you suck fuel along the underside of the car, where heat from the engine can warm the fuel lines, you help the fuel boil over.

"suction style" fuel pumps cannot pump vapor; you can wrap all the clothes-pins and cow magnets around the portion of the fuel line that you can see - the "pressure" side from the pump to the carb. - but that wont change what happened in the "suction" side of the gas line between the tank and the fuel pump.

Fuel and car engineers correctly recognized if they lowered the boiling point of gasoline, cars would be easier to start during the cold winters of the north-east.

As the "Reid Vapor Pressure" went up, Packard Service Bulletins by the early 1930's were full of articles trying to resolve the vapor lock problem.

The symptoms described by the fellow who started this "thread" suggest it is a simple problem of using modern fuels in a pre-fuel injection vehicle. Which explains why a electric fuel pump (which pressurizes the fuel line, thus preventing vapor lock) is the simple and permanent solution.

I have no real idea - only some suspcions, as to why some of the later pre-war "junior" Packards and most of the post-war ones - again - SOME, do not seem to be afflicted with the "vapor-lock" disease. Could it be that Packard engineers figured out a way to keep the fuel lines cooler than the earlier models ?

As a side note - don't make the mistake of thinking "we all use the same gasoline". Nonsense ! Depending on the season you are in, and/or the region you are in, the Reid Vapor Pressure of gasoline is changed by the refineries, to best meet the needs of the average driver in that area. Well...that WAS the case during the carb. era - I don't know if they still bother to do that now that you cannot buy a new car with a carb - all have high pressure fuel pumps located IN the gas tank.