Air Cutoff Valve contradiction.

[yrunvs]

I'm trying to diagnose a small amount of burbling and popping on low RPM decel and throttle unevenness just off idle maybe up to 2200 rpm. Could be slow jets, carb galleries, etc. But I've noticed mention of air cut off valves a lot as being a culprit. So reading up on them I'm getting a little confused as much of the literature says that when they fail they will cause problems and then the next sentence says that they have no effect on performance?? Read this and tell me what I'm missing.
https://www.motorcycleproject.com/text/aircut_valve_more.html   

[Ricky-D]

Nothing wrong with that....

The air cut valve is/was designed to help eliminate popping upon deceleration.

An off-idle gurgling and popping is usually (90% of the time) clogged carburetor passages.

Strong doses of an additive will normally clear up the problem after a few tankfuls.

Naturally, this is dependent upon how the engine was running beforehand.

Not to forget to mention, that any modification to the exhaust will void the design parameters.

***

[yrunvs]

But as I read it a non functioning air cut off valve will not be doing its job of adding fuel during decel thus contributing to a lean condition thus the burble/popping is not that a performance issue?

[Jersey]

But as I read it a non functioning air cut off valve will not be doing its job of adding fuel during decel thus contributing to a lean condition thus the burble/popping is not that a performance issue?

It may be that the reference to "performance" is about acceleration, cruising, mpg, etc.  Popping during deceleration might not be associated with a performance state, since the engine would be reducing rpms to idle.   Just a guess.

I do know, that I had a bad Air Cutoff Valve that caused popping on Decel.  I replaced it and all was good.

[Ricky-D]

But as I read it a non functioning air cut off valve will not be doing its job of adding fuel during decel thus contributing to a lean condition thus the burble/popping is not that a performance issue?

Read it again.

It does not say anywhere that a bad c/o AV adds fuel.

***

[yrunvs]

But as I read it a non functioning air cut off valve will not be doing its job of adding fuel during decel thus contributing to a lean condition thus the burble/popping is not that a performance issue?

Read it again.

It does not say anywhere that a bad c/o AV adds fuel.
G
***

You are correct. It restricts the air side of the equation.

[RonW]

I think the function is to introduce *air* in the pipes on decel. If the air tubes are clogged, the restriction reduces the volume of air introduced in the pipes. Pic is of the bottom (middle) air tube. I don't know how clogged the front and back air tubes can get. The middle air tube's bracket (pic) faces up.

[WintrSol]

I think the function is to introduce *air* in the pipes on decel. If the air tubes are clogged, the restriction reduces the volume of air introduced in the pipes. Pic is of the bottom (middle) air tube. I don't know how clogged the front and back air tubes can get. The middle air tube's bracket (pic) faces up.

That's the PAIR system. The air cutoff valve is mounted to the side of the carb, and is activeted by high vacuum in the intake tubes, changing the flow through the pilot circuit. The PAIR system is activated by vacuum in the headers.

[98valk]

I'm trying to diagnose a small amount of burbling and popping on low RPM decel and throttle unevenness just off idle maybe up to 2200 rpm. Could be slow jets, carb galleries, etc. But I've noticed mention of air cut off valves a lot as being a culprit. So reading up on them I'm getting a little confused as much of the literature says that when they fail they will cause problems and then the next sentence says that they have no effect on performance?? Read this and tell me what I'm missing.
https://www.motorcycleproject.com/text/aircut_valve_more.html   

All gas IC engines pop during decel, when everything goes lean. closed mufflers keep one from hearing it. super lean out of tune causes very loud pops.

unevenness at 2200 rpm, is idle mixture screws.   

http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

[yrunvs]

Thanks for that info. Would a faulty.air intake unit be considered a vacuum leak?

[RonW]

That's the PAIR system. The air cutoff valve is mounted to the side of the carb, and is activeted by high vacuum in the intake tubes, changing the flow through the pilot circuit. The PAIR system is activated by vacuum in the headers.

My bad.