I've got a few problems hapening wth my q-jet, and I'm sure 2 of them are related, hopefully the 3rd is as well.

Problem 1:

I need to replace the little accelerator pump piston. It bleeds off too quickly. When I get ready for a drive, I pop the hood and pump that piston up so I know it's filled with gas (2-3 full pumps before it starts sending gas through, probably 8 or so full presses before it's full). But if I'm on the highway for 20-30 min, I can tell it has already bled off some (delay from normal to WOT get's larger and larger). How much do I need to take off to replace that piston? Is it easiest to just remove the whole thing?

Problem 2 (related I hope):

When I press the accelerator pump, there's no real spray, it just comes out in streams, one in each primary barrel. I'm thinking once I replace the piston, this will clear up, I hope...

Problem 3:

When I've been hitting the back roads, and getting on it for a while (lots of little bursts of heavier acceleration) it seems like it runs out of gas. Ill put my foot down and Ill get something like "vroooOOO---OOO----OOOO--oooOOO---oooOOOOoo--ooooommm". Once I take it easy for a minute or two, it's back to normal.

74 L-48 btw.

Thanks for the input guys. Just a heads up, I'm no mechanic, so you'll probably have to speak to me like a child (see "vrooOO--OOmm")

Miles

 

I think that you're confused as to what the "accelerator pump" actually is. It is not a "pump" in the usual sense, in that it doesn't draw fluid in and force it out. It doesn't bleed off. It's like a child's squirt gun. The fuel bowl and accelerator pump reservoir is filled by the engine fuel pump, and when the accelerator pump is depressed two streams (not sprays) of fuel are squirted into the air-stream. It sounds as though your fuel filter may be clogged, engine fuel pump may be marginal or vapor lock is preventing proper fuel delivery. It's not difficult to change the accelerator pump, but unless you have some experience I would advise having a professional replace it and the filter. If you want to tackle this job yourself, search online or read a Qjet book before you do anything.

 

I replaced the fuel filter in the front of the carb this weekend. It didn't look to be clogged, but I replaced it anyway since it was already out.

I took the carb apart in high school, and said I would never do it again .

I was almost certain the accelerator pump (radiator/driver side corner of the carb) was just a little piston that had a rubber skirt around the bottom of it that would create a suction when depressed and it would draw in fuel to fill it's cylinder from the fuel bowel.

Could it be possible that the float in my carb is adjusted to sit too low and not allowing the bowel to be filled to where it should be?

Miles

 

I think you hit the nail on the head. This would be the first thing I would check as well.

 

if this is a sudden change in performance, the float level will not change unless something is worn out. Either bad accelerator pump or needle and seat wear causing float level to change or float is compromised. No matter what you have to disassemble the top of the carburetor. So you may want to have on hand a new needle and seat, new accelerator pump, and possibly a new float plus the airhorn gasket.

 

the accelerator pump does not pump into the bowl, it squirts out into the venturi. it's job is to mitigate the bog you would get when you quickly open the throttle and the venturi effect cannot react fast enough to draw enough fuel and stalls out. when it's bad, and you punch it, it stalls, or you have to pump the gas pedal quickly to keep it running or accelerate very slowly. it does not "mist" it's just a stream.

it does sound like a bad accelerator pump. if it takes 8 pumps to get it to squirt, it's the seal failing. when you get on it like you describe, the vroom, ooom, vroom, is the venturi pressure catching up with demand...

 

take it to a qualifies mechanic, or joi na corvette car club, have someone from there help you.

 

If it gets worse as you drive then recovers if you cruise easy for awhile, it may be the sock screen in the fuel tank getting plugged.

 

All above great suggestions. I'll add one more. Check the S hose from the pump to the line going to carb. S hose is a formed hose that needs to be used so the line does not crimp. If you have a straight piece of rubber fuel line look at it closely and I guarantee its crimped.