Bench testing my combination fuel pump vacuum question

Posted by calcustom8 On 2009/8/29 23:01:43

Hi Guys,

I am in the process of rebuilding the combination fuel / vacuum pump for my 22nd Custom 8. While on the bench, I can tell that the fuel pump is working. When I push down on the lever, I get suction on the "in" and pressure on the "out" but the vacuum portion seems to just "sit there". Investigating, I found that the diaphragm spring is pushing the rod all the way in such a way that the levers take no action.

Is my test valid? In the back of my head I am thinking that maybe some other conditions have to be met before the vacuum pump starts working. (full throttle passing a car in the rain) It is almost as if the spring is on the wrong side. (it's not, I checked)

Any clues or advice?