[quicksilver97ta]

My qjet has a dead spot in the pump shot. I observed this as I was looking for a reason why the carb seems so cold natured despite following Cliff’s calibration suggestions which I believe to be spot on. The shot will start immediately with any quick throttle movement so that part is correct however, about midway through the pumps range of motion the shot will stop/interrupt and immediately resume with even more flow. It’s like I have two sets of squirters but they don’t overlap. I have Cliffs acc pump. What could this be? Is the pump seal binding? Or could it be a problem with the checkball? It’s very repeatable, almost as if it’s there by design.

[Kenth]

Only one way to find out, pull the airhorn off.

May be swollen cup or pump duration spring retainer binding in bore.

[67cruiser]

Kenth is dead on, reseat the check ball first and easiest, check spring & cup, if its Cliffs pump, dought very much if thats it thou.

[quicksilver97ta]

Originally Posted by Kenth

Only one way to find out, pull the airhorn off.

May be swollen cup or pump duration spring retainer binding in bore.

Carb is on the bench, airhorn is off. Everything "looks" fine. So it does sound like something is binding? I was thinking of taking off the garter spring for testing purposes and repeating.

[Doug Hopkins]

I had a Q-Jet on a 86 Chevy truck with a lot of mileage that had the same problem. I found the pump bore in the bowl to be worn or improperly cast in the middle of the pump shot. I would put in a new pump about every four months and eventually replaced the carb.

[quicksilver97ta]

Pump seal binding/swollen?

I tried another pump I had and it’s clear the old one was sticking causing a jerky motion. The cup looks very similar but the new one is just slightly narrower. The old one has been in service for about 2.5 years with E10 pump gas. I do not know if the old one is swollen or puckered out or if it is just made slightly different. Also, I noticed the spring design is different. I’m not completely sure which or if both of these differences is making the difference but there is a definite difference. The new one starts with a more vigorous shot, it’s uninterrupted, and actually is exhausted quicker via the throttle body range of motion. I’ve got no experience with swollen cup seals, only hardened rubber ones. The old one is still very soft. In any case I’m sure glad I found this and cant wait to get it back on the car!

[Blued and Painted]

I like to wrap part of a green scuff pad around some kind of small anvil and lightly hone the pump bore. After honing, the rest of the pump circuit would have to be disassembled and throughy cleaned. No biggie.

If you cut/grind an 1/8" off the pump shaft, it will position the cup higher in the bore (virgin bore) and give you a longer pump shot.

All old girls need a longer pump shot to get the desired effect.

[Cliff R]

The pump in the top pic has the wrong spring on it, make sure if you use that pump to install the spring from the bottom pump on it, or it will coil bind and could cause major issues when placed in service. Neither one of those pumps appears to have a swollen or defective seal on it.

The pump we sell has a dark blue seal, it will have a noticeably thinner lip and be tougher and firmer than a blue seal from an over the counter kit or other supplier. I've never had one fail to date. We switched to them a couple of years ago, before that we were using the seals on the pumps from the supplier. They were a lighter blue material and softer. Had a few of those swell up in contact with this new fuel, so had to go to a much better part, which has proven good, even in E-85 applications.

The pic shows the blue and black seals being replaced with our seal........Cliff

[quicksilver97ta]

Thanks for the clarification Cliff. The diameter difference in the seals is very slight. I tried to get a pic of them inside a dial caliper but I just couldn't hold everything and the camera phone. But that spring is definitely wrong then.

[Cliff R]

Yes, too man coils, most likely from a pre-1975 unit. Use the later spring with less coils no matter which pump you are installing....Cliff