general carburetion question

[spudspuppy]

Hi all,

This is something that I've experienced on two vehicles and have never found a definitive answer for.

What is the main cause of "engine bog" on acceleration? I've only noticed this from a dead stop. Stomping the pedal to the floor causes the engine to bog down and requires I lift the pedal slightly to get acceleration. Is this due to undersized jets? Air quantity? air/fuel mixture?

In one instance the vehicle in question had a 4 barrel carb (both a rochester quadrajet and a holly - at different times). In the current instance on my 92 Silverado, I have the stock TBI system. However, the engine has been rebuilt (slightly bored over) and is running headers without cats. I should note that from a rolling start (10-15 mph), flooring the accelarator results in rapid acceleration as I would expect.

Any thoughts appreciated.

Spudspuppy

[70camaro]

With F.I. check your fuel pressure, injectors, spark timing and advance, MAF, vacume leaks, etc. With a carb there could be several additional causes within the carb itself. Those are the basic things. ECM controls could affect it too. hope that helps.

[pind]

could be that the accelerator pump is worn out, and not delivering enough of a shot of fuel to the engine when you hammer it. it should shoot a substantial amount in at the initial stomp.

[Pamsdad]

Spuds

The Quadrajet has a HUGE Secondary Air Valve. It is controlled a couple of different ways. There is a tension spring and a choke pull-off. The spring must have the right tension and the pull-off must be functional. Otherwise the secondaries are overcome with too much air at once. There is no accelerator pump that can keep up with it.

As far as the Holley, was it vacuum or mechanical secondary?

[spudspuppy]

Pamsdad,

Thanks for the input on the quadrajet. As I recall, the Holley was probably a mechanical secondary. As it was a Buick 350 engine, I also had to get an intake adapter to mount the Holley. I always attributed the bog to my inadequate knowledge of air/fuel mixture stuff. And it looks like I was right. I had rebuilt the Quadrajet a time or two, but paid no attention to the spring or the pull-off.

On my 92 Silverado, I have the stock TBI system, which does the same thing. 70camaro gave a listing of things to check with that system, so I guess I have my work cut out.

Thanks
spudspuppy

[gtmud]

With your carb, check your air/fuel mixture screw settings, and your timing. Its more a "feel" for it. Work your timing in as close as you can, then fine tune it with your mixture screws.

[Mikado14]

Spuds,

What Pamsdad said. It took me several tries with that damn Quadrajet when I rebuilt it but finally got it right.