Popping on deceleration

I read on a Honda forum that if the exhaust pops on deceleration it indicates that the bike is running lean. Anyone know why that would be?

 

Don't know why, but heard the same thing here.
I had a popping on deceleration - then I rebuilt carbs (replaced 30 year old throttle shaft seals) and the popping went away.

I used to have a 75 IH Scout (slant 4) with a cherry bomb muffler on it . . . You wanna talk about popping on deceleration? I would set off car alarms with it! The things that I thought were cool as an adolescent not so much now . . .

 

Yes.

 

I guess I should explain.

First, a lean mixture burns hot. This results in hotter than normal exhaust gasses.

When closing the throttle the engine vacuum increases, but the slide closes cutting off fuel from the main jet. The difference in pressure causes fuel to be pulled in from any available passage (the idle circuit (and en enrichment circuit if it's open/leaky)) as quickly as it can be drawn in. This results in a richer than normal mix.

During valve overlap some of that rich mix is dumped into the exhaust.

Remember what a lean mix does to exhaust temps?

POP!!! Ignition of the rich mix inside of the too-hot exhaust.

 

Makes sense. I assume no damage to the engine but perhaps to the exhaust if too much.

 

If you let a lean condition go on for too long you'll end up with a hole in the piston. Of course that depends on how lean it is.

 

My 2001 Honda 750 Shadow ACE with 37,000 miles is bone stock and it has always popped a little if I fully close the throttle. The carbs have never been touched so they still have the factory settings. I normally never fully close the throttle so it's not normally a problem. I wouldn't think the factory setting would be so lean so as to cause a problem--at least I hope not.

 

OH. Ya, they do that. Honda set them lean to meet emissions, but safely lean (liquid cooled engines have greater safety factor). My son's ACE used to do that too. Now it only pops if you goose it a little before slamming the throttle shut. Be sure not to do that in the neighborhood at midnight; it'a very big pop ....lol

 

I'll keep that in mind for the 4th!

 

Does this condition sounlike a 'pop' like gunfire or popcorn, or a mild 'gurgle' when decelerating?

 

It can be either. Depends on how lean and what the exahust system is.

 

When mine was doing it, it sounded like a rather cool gurgly pop, popping.
Too bad it isn't an ideal tuned condition . . . .

 

I guess it is more of a gurgly popping. Certainly not a gun shop type. It only does it if I totally close the throttle. Sounds like an old car I used to have, so I'm ok with it--just wondering.

 

The VT1100 ACE engine is really kind of a dirty-burner as engines go. So the stock tune is pretty much ideal for meeting emissions requirements and still having a strong-pulling engine.