Re: vacume tank or vapor lock 1929 626

Posted by DavidM On 2012/9/1 18:08:22

The car in question is a 1929 626 and strangely the Packard parts list for that model does not call for insulation on the exhaust pipe although it is specified for other similar models however I have fitted insulation to my 1929 633 (which is identical). I am sure it helps but I think the main problem is radiant heat from the manifold to the vacuum tank due to the close proximity of the tank to the manifold, hence the need for a heat shield..
I once had an interesting conversation with the owner of an early twin six (they are notorious for vapor lock) and he had tried many things and found the best improvement was fitting a vent to the carburettor float chamber. He stressed that it had to be at least 1/4 / 3/8" dia tube to be effective.
As a matter of interest, hold you ear to the vacuum tank when the car is hot and you will hear the fuel boiling inside, this does necessarily mean it is vapor locking, it is the very low boiling point fractions boiling off. But it shows how close these cars are to vapor locking with a little more heat.