Re: vacume tank or vapor lock 1929 626

Posted by Tim Cole On 2012/9/2 7:21:15

Dear 29:

Get rid of the fuel filter. It is a restriction. If you are having a dirt problem the a filter should be installed before the vacuum tank. The vacuum tank will pull through a filter given the motor is in good condition, but will inhibit sustained full throttle.

If you think the manifold is causing problems you can test by making a heat shield.

Check your compression and motor vacuum. The vacuum tank will cause problems in worn motors and will need to be bypassed using an Airtex electric (available from Hirsch) and a 1 psi fuel pressure bypass (available from McMaster-Carr).

To test the tank, buy a hand vacuum pump and plug the fuel line. The unit should hold vacuum. Next fill the tank via the hand pump to pull gasoline from the tank. If it doesn't fill you have a valving problem. Or an air leak in the pickup circuit. Brave souls can simply suck on the line to fill the tank. (Heavy smokers will probably have some problems.) Those old tank pickups are prone to pin holes as well.

Dirt in the fuel will cause absolute havoc with the vacuum tank, so if the gas tank isn't in good condition that needs to be addressed. (Apparantly those old globe type gasoline stations were pretty good at delivering clean fuel to gas tanks).

You can confirm you have a vacuum tank problem by filling the unit during a no start situation, but do not overtighten the fill plug as the pot metal is old and delicate. Snug with your finger should be plenty.


Hope this helps.