| Author | Message | ||
     Kalali |
I am trying to understand what caused the decel popping when I switched to a V&H slip-on. When I originally posted this issue/question most folks responded by saying that the mixture got too lean, etc. But technically speaking, isn't the popping caused by the gas burning in the exhaust tract, which would imply a rich mixture? Same thing about backfires..Why would a lean mixture cause backfire? Somehow I don't find the logic intuitive... Thanks. | ||
| Rich |
If the mixture is rich enough, there isn't enough oxygen for ignition. | ||
| Djkaplan |
When you close the throttle quickly (on a carb or FI engine) there is a momentary period when the mixture gets rich because air is suddenly reduced and it takes longer for fuel to lean out to match it. This only happens in an instant (and creates a puff of pollutants). Once this rich period is over (when air flow again matches fuel calibration) and you are still coasting, you have an engine running at an RPM much higher than idle speed but with only idle speed fuel mixture flowing through the carb (or FI). This creates a mixture so lean, it doesn't 'light off' properly when it's supposed to be ignited by the sparkplug. The unburned mixture is then pushed out on the exhaust stroke where the pressure and the hot environs of the header pipe ignites what's left. That creates the familiar 'popping' on deccel. The reason modern bikes and cars don't return to idle quickly is because the throttle has a return damper to keep the throttle from closing quickly. This is to pass EPA emissions tests, but it also helps keep the popping down. Next time you're on your bike, you'll notice the popping will go away (or lessen) if you keep the throttle slightly cracked open. | ||
| Mm128 |
Mine does it with the Race Setup from Buell... I think to a certain degree its kinda NORMAL..... All of the Buells that i have owned have done it with the Race Systems installed... Matt | ||
| Langperf |
Any well tuned system will not pop and carry on in a decel condition. You can look at any new car or bike, performance or not and if it is running correctly in stock trim, you can decel the hell out of it and it will not afterfire (technically a backfire would be into the intake tract) the popping comes from a lean condition where the unburned gasses actually detonate in the exhaust due to excessively high heat and the unburned byproducts of a lean fire in the cylinder. A to rich condition on decel will lead to (in more extreme conditions) fire coming out the exhaust, the unburned mixture will burn not detonate. What you see on some of your V8 stock cars under heavy engine breaking. None of my performance vehicles, Buell or otherwise pop on decel and they are all modified. The downside here is there is no magic way to eliminate it. It takes a lot of tuning time to get it just right. I just have to bite my tongue every time I'm sitting at the local biker hangout and the guys next to me are talking about how the guy at the dealer said popping out the exhaust on there bike is normal(I believe some dealer personel truly believe this). Wrong. Now wether they have the knowledge, or money to pay someone knowledgeable to get it right is another story (Very time consuming). So believing it is normal may put them at peace with that ill running beast. DJ...I havent seen a throttle plate damper in years(Throttle damper = Lawsuit), any RPM delay before returning to a true idle is done with the Idle air valve (IAV) or Idle air solenoid (IAS) And from the auto engineers I've talked to this is mainly in effect (or where it would be noticeable) on stick shift cars to aid the manual transmission shifting impaired. (believe it or not)Surprised me. Holds the RPM up a bit whilst they complete their shift. | ||
| Thatdudejoe |
Kalali, I have the same problem on my S1 (with V&H slip-on), and it seemed to get worse when I wrapped the headers. However, I had to drill out a pesky exhaust stud in the head and use a helicoil, so I have just assumed that the popping was from an exhaust leak. Leaks may be a cause too! | ||
| Kalali |
Thanks everyone for the thorough explanation. It does now make sense to me why a lean condition would contribute to the decel pop. When I switch back and forth between the stock and V&H exhaust, the decel pop completely goes away which supports Langperf's comments regarding a well tuned motor; e.g., stock ECM maps, etc. I do understand what needs to be done to get rid off it; race ECM or ECMSPY tuning, but the lean vs. rich thing is now cleared up for me. Thanks again. | ||
| Skntpig |
I had my V8 car tuned and one of the options was to retain the factory pop when downreving. The other was to introduce a small bit of fuel and it stopped the pop and smoothly downrevs. It was called DFCO Decel Fuel Cut Off and is easily heard on any most newer high performance cars and best heard with an aftermarket exhaust. Ever heard a loud Camaro or T/A pop and carry on? My S1 doesn't pop much at all with a KT pipe, but I jetted for days until it was spot on. | ||
| Bad_karma |
Make sure that you don't have any exhaust leaks. Use high temp O2 safe sealer at the elbow and can junction. Joe | ||
| Kalali |
I will check. BTW, where do you find "high temp O2 safe sealer"? Any specific brand? | ||
| Silas_clone |
I get a bit of popping, but more noticeably, the bike stalls at low rev deceleration. It starts right up when cold and idles M2 |
