Q jet Bog

[greggome]

Had my 68 Q jet rebuilt by allstate carburetor about 6 months ago and its been working fine. I suddenly started having significant hesitation issues when i stomp the accelerator pedal. Car cruises okay though I have noticed a very slight hesitation feel when changing gears and press accelerator normally. Under heavy acceleration the car bogs and almost sounds like it could stall but as soon as I back off the pedal it resumes cruising. just recently installed AC Delco R 45 plugs instead of the cooler Champion RJ12YC plugs I had been running (local driving cooler champion plugs were too rich , new plugs nice tan color). Also I had just flushed cooling system. Dont think these things would cause the bog. Any thoughts how to trouble shoot this?

[429bbf]

id try a couple things  first id change the fuel filter and then id test the accelerator pump and see if the cup has swelled up and not pumping fuel . fwiw

[Dogmeister]

Check your air valve spring tension. If it's too lose it can cause hesitation. Start with a half turn after the spring contacts the pin. You may need 3/4 - 1 turn. Make sure you tighten the locking screw when you're done.

[greggome]

not sure the location of this spring. I see the external spring that attaches to the secondary shaft.  Anyway to check this spring tension without pulling the carb? Carb only has been run for 1000 miles since rebuild. I'm surprised anything like valve spring adjustment or accelerator pump would be out of wack.

[Cliff Ruggles]

Most likely the accl pump seal and/or pump has already failed.

Very common problem and EXACTLY why I have much better accl pump seals made as NONE of the "blue" ethanol resistant seals you will find in rebuild kits will last very long in contact with this new fuel.....no matter what they tell you......Cliff

[greggome]

While trying to correctly diagnose the problem before tearing my carb apart, I ran across this online info from thecarburatorshop.com "It is very easy to test the function of the accelerator pump. Start the engine, and warm to normal operating temperature. Shut off the engine. Remove the air cleaner. The choke butterfly should be fully open, as the engine is warm. Observe the pump jet in the carburetor, and with your hand, work the carburetor throttle to the wide-open position. You should observe a healthy squirt of fuel from the pump jet."

I have followed this method and i do have a good squirt of fuel from the pump jets. Wouldn't this confirm the proper operation of the accelerator pump?

[Cliff Ruggles]

Not always as the seal can still push some fuel with a rip or tear in it and that test woln't tell you if the check ball isn't sealing well and allowing fuel above the check ball to drain back into the carb causing a delay in delivery from the pump (common problem)......Cliff

[greggome]

Never tried tearing a Q jet apart. To replace the accelerator pump seal apparatus are there any diagrams/instructions available as to the disassembly procedure?

[Cliff Ruggles]

Accl pump replacement only involves removing the airhorn, and at most you would need besides the pump assembly is a new main body to airhorn gasket.

Our top gasket for those early units is .015" thicker than stock and much better material, plus when you order our pump you get the entire assembly with new springs/retainer, and it's lifetime warranty......Cliff

[greggome]

Since the bog takes place when I am driving and press the hard on the accelerator should i expect to get the same bog when I stomp the gas while in neutral if the accelerator pump is the culprit ?

[Cliff Ruggles]

Not always as engine there is no load on the engine and it would require much less accl pump shot to cover a lean condition.

I would install one of our accl pumps and be done with it. It is far superior to anything Allstate would be using and has a lifetime warranty.....Cliff

[Dogmeister]

Obviously Cliff is The Master here, but I still suggest putting a little more tension on the air valve spring to see if that helps. Doesn't require disassembly. Fixed a significant bog on mine. I PM'd you with instructions.

[Montecarlow]

I know this is an old post, but it would be great to see instructions here in the post. Specifically the location of the secondary air valve tension spring, and where to tighten the locking screw when your adjustment is finished.

[Kenth]

This might help some.