Decel Popping when Hot

[srigas]

Got a map from Dynojet that works quite well except I get a big decel pop between 2700 and 2900 when I let off the throttle. This only happens when the bike has been ridden for 15 or 20 minutes. Up until then there is no popping in that rpm range. Anyone have any ideas what might be happening? I can't seem to tune out the big bang. I have replaced exhaust gaskets and the efi carb gasket between carb and air cleaner back plate as well. Thanks for your thoughts.

[Dave63]

Please introduce yourself in the New to the Community section. I also see you posted the same question on the V-Twin forum.

My *guess* is that you're running lean in that range, but without knowing what pipes you have (backpressure) or without a Dyno run with a gas analyzer, it's only a guess....

It may be lean, or it may be nothing other then decreased backpressure resonating at that specific rpm range.

[srigas]

I have the V&H Big Radius 2:1 pipe. I really like it. Also have the powercommander. I've been trying to richen my map up and even Dynojet has made changes to the maps, but still issue continues. I just haven't had a chance to get to a dyno. Thought I could buy some time, but I guess not.

[Dave63]

It may just be that specific pipe, making noise at that time, but like I said, without a dyno run, you're never going to know for sure. PC also allows you to go into the mapping and change lean/rich settings at specific rpm ranges, which if you did that and still have that noise, that leads me to believe it's the pipes, themselves.

[Blackdog 15]

Try adjusting your PC up one bar...that will richen you 5% ..do it in the mid range...also check your plugs...run down the road at 3,000 rpm, hit your kill switch and coast to the side of the road...pull your spark plugs and check them for color...

Black = rich
white = lean
tanish = just right.... this is how I fine tune my scoot...

[blackwell33]

You said that you get the popping when you let off of the throttle. Is your throttle completely off? or are you just rolling it back slightly? I'm guessing it is when you let off completely.

Open up your power commander software and the current map that you are using. As you will see, there are 2 areas that you can tune in (The "fuel" and "ignition"). You want to look in the "ignition" section.. and you will be able to change values for the front and rear cylinder. make sure you do BOTH.

Since you are hearing the decel pops in the "0" throttle position (meaning not twisted at all) you will need to make changes in that column. All of the values there currently should be a "0".

In the 0 column, in the rows between 2k rpms and 6.5k rpms, change the value "0" to a value of "15" or "20". I am personally using 20 right now (and 15 in the "2" throttle position).

Do not change values below 2k, as it will affect idle.

if you are 100% certain that you are only hearing the decel pops between 2700 and 2900, then start by just adjusting them in that range.

Its ok to make changes to the map and send them to the power commander while the bike is running.

here is a close screen shot to give you an idea of what i am talking about. try this and then take the bike out to warm up as usual and let me know if it helps. It cured mine like magic.

Let us know..

safe riding..

[srigas]

Here is my map. You can see that I have beefed up the zero cells. Still get that bang. Thanks for the help.

[blackwell33]

Not insluting your wrenching abilities, just trying to cover all bases.. did you torque correctly on the exhaust? I don't torque, I just use a good snug fit, and I always make sure I have 3 threads showing, then I know I am good.

Also, did you replace the exhaust gaskets with the HD ones or the screamin eagle performance ones? The SE ones are thinner and are a bit harder to get to seal.

If it's neither one of those, and you have 100% ruled them out, I would think it's just the pipes and how they resonate at that given rpm.

There are a couple of posts on here about a home made "baffle" that you can try. Dave has one version in the exhaust forum called "drag pipe blues" and I have one in the sportster section called the "lollipop mod". They're both tuneable and cheap. Check out those threads.

[srigas]

Yes I did replace the gaskets with the SE ones and checked all exhaust nuts. I even changed the carb gasket to the air cleaner base. I think I'll just get it to a dyno and see what the real issue is. It just may be the pipe as you say.