Decel pop, what's the real story?
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Stellar HDF Member
Joined: May 2010
Posts: 2,864
Likes: 126
From: Aussie lost in Switzerland
Decel pop, what's the real story?
Many of us go the route of fuel managers, xied's etc for better performance, but many also cite decel popping as something to be killed at all costs!
What I haven't seen is an explanation as to wether or not decel popping is actually a bad thing. I can understand extreme popping may not be doing you any favors performance wise, but is it bad for your engine, especially since it occurs in your pipes.
I run my bike with V&H straight shot slip ons, Sceaming Eagle open AC and ViEDs. I have the ViEDs tweaked to what I believe is as close to perfect as I can get and the bike runs really well. I spend a good amount of time in the power band because the roads here are just awesome twisty heaven and I love riding them.
I get a nice throaty "burble" on decel, and very occasionally a good loud backfire under decel if I drop it down a gear in the power band for a hard engine brake. I don't plan to change the setup because the bike performs beautifully and I am satisfied with the setup.
For those considering fuel management of some sort, could the forums collective wisdom explain if decel popping is actually a bad thing, aside from being annoying to some, and if it is something that should be the subject of a life quest to kill, and why?
What I haven't seen is an explanation as to wether or not decel popping is actually a bad thing. I can understand extreme popping may not be doing you any favors performance wise, but is it bad for your engine, especially since it occurs in your pipes.
I run my bike with V&H straight shot slip ons, Sceaming Eagle open AC and ViEDs. I have the ViEDs tweaked to what I believe is as close to perfect as I can get and the bike runs really well. I spend a good amount of time in the power band because the roads here are just awesome twisty heaven and I love riding them.
I get a nice throaty "burble" on decel, and very occasionally a good loud backfire under decel if I drop it down a gear in the power band for a hard engine brake. I don't plan to change the setup because the bike performs beautifully and I am satisfied with the setup.
For those considering fuel management of some sort, could the forums collective wisdom explain if decel popping is actually a bad thing, aside from being annoying to some, and if it is something that should be the subject of a life quest to kill, and why?
Road Master
Joined: Aug 2012
Posts: 1,086
Likes: 5
From: London, UK
True, but the matter is made worse by the oft-suggested fix of adding more fuel!
Since it is the combustion of unburnt fuel in the exhaust, the solution to me seems to be to reduce the amount of unburnt fuel in the exhaust. Making the mixture more lean in these regions might help a little, but I'm now leaning towards advancing the timing to try and get it all burnt within the cylinder. Because the engine is under no load whatsoever, there is no danger of damage from pinging, so should be a pretty safe option.
Since it is the combustion of unburnt fuel in the exhaust, the solution to me seems to be to reduce the amount of unburnt fuel in the exhaust. Making the mixture more lean in these regions might help a little, but I'm now leaning towards advancing the timing to try and get it all burnt within the cylinder. Because the engine is under no load whatsoever, there is no danger of damage from pinging, so should be a pretty safe option.
Elite HDF Member
Joined: Apr 2008
Posts: 4,718
Likes: 11
From: Back in the Good Ole USA. South Carolina to be exact.
True, but the matter is made worse by the oft-suggested fix of adding more fuel!
Since it is the combustion of unburnt fuel in the exhaust, the solution to me seems to be to reduce the amount of unburnt fuel in the exhaust. Making the mixture more lean in these regions might help a little, but I'm now leaning towards advancing the timing to try and get it all burnt within the cylinder. Because the engine is under no load whatsoever, there is no danger of damage from pinging, so should be a pretty safe option.
Since it is the combustion of unburnt fuel in the exhaust, the solution to me seems to be to reduce the amount of unburnt fuel in the exhaust. Making the mixture more lean in these regions might help a little, but I'm now leaning towards advancing the timing to try and get it all burnt within the cylinder. Because the engine is under no load whatsoever, there is no danger of damage from pinging, so should be a pretty safe option.
Road Master
Joined: Apr 2008
Posts: 935
Likes: 1
From: Indiana
I'm confused. Should I increase or decrease fuel at 0% throttle? Running PC-V. Currently fuel enrichment are at 0 at closed throttle.
If there is unburnt fuel causing the decel pop, Shouldn't I decrease fuel instead of adding?
If there is unburnt fuel causing the decel pop, Shouldn't I decrease fuel instead of adding?
Road Master
Joined: Aug 2012
Posts: 1,086
Likes: 5
From: London, UK
So there are three ways of stopping this from happening; make the fuel mixture too rich to burn (add fuel), make the mixture too lean to burn (remove fuel) or reduce the temperature in the exhaust (add fuel). The problem with the last is that the temperature only changes slowly (compared to conditions inside the engine) and so unless you can cool the exhaust under all engine conditions, this cannot be solved in one area of the AFR table.
So we are left with either
a) adding fuel by decreasing AFR in the 0% throttle/Lowest MAP columns. If you add enough, you'll make the exhaust mixture too rich to burn. But the result is just spraying your expensive gas out of the exhaust unburnt.
b) removing fuel. You can try increasing the AFR, but you're limited in how high you can go before the table maxes out. If you can't go any higher, what's left to try?
c) burning more of the fuel in the engine. By increasing the timing in the relevant area, the mixture starts to burn in the engine earlier. The load is almost non-existent, so the danger from pinging is tiny and we should be able to increase the advance considerably before seeing knock events. By igniting the mixture earlier, it has more time to burn in the engine before being thrown out the exhaust.
Let us know how each of these options plays out for you.
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Big Kahuna HDF Member
Joined: Dec 2012
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From: .....
Mine does it and I was told, it the kind of pipes I have. I've gotten use to it after 4 months.
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Grand HDF Member
Joined: May 2007
Posts: 3,870
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From: Alberta
FWIW; my '01 103 FXDXT at 111hp/117ft lbs with 2" Cycle Shack M pipes (stock looking) NEVER popped on decel...fuel was handled by a CV51; no carb vs efi thread starting here!
The bike also got exactly 10% less fuel mileage than the wifes 08 FXDL with a 96" stg 1 engine. No change in our retirement plans with that difference.
Waaay back in the mid 70's I had one of the first gen Goldwings and there was an enrichment circuit for closed throttle...kept the ultra quiet pipes from farting...at least that's what I think it would've sounded like.
My current 08 FXDF pops a lot less with my RB Racing Black Hole than it did with the V&H swoopy 2-1...will be re-tuning when I change cams and see what happens.
The bike also got exactly 10% less fuel mileage than the wifes 08 FXDL with a 96" stg 1 engine. No change in our retirement plans with that difference.
Waaay back in the mid 70's I had one of the first gen Goldwings and there was an enrichment circuit for closed throttle...kept the ultra quiet pipes from farting...at least that's what I think it would've sounded like.
My current 08 FXDF pops a lot less with my RB Racing Black Hole than it did with the V&H swoopy 2-1...will be re-tuning when I change cams and see what happens.