Jump to content
Sign in to follow this  

Why More Decel Popping After Repack?

Recommended Posts

Hi-I just repacked my Pro Circuit Pipe and used a supposedly better packing material from FMF (it has metal screen and several layers of stuff). It is supposed to last longer than the regular packing I have been using (also from FMF). The exhaust is quieter at idle now, but when riding the decel popping is bordering on obnoxious. I've checked for exhaust leaks and have none, so what else would cause this? Do I need to adjust jetting? It seems that a repack shouldn't make that much of a difference on air-fuel ratios.

Also-unrelated but what are the symptoms of a worn chain and sprocket before it starts jumping teeth? I've got about 13,000 miles on the stock chain and sprockets and am starting to wonder if it is due for replacement. I have never had to adjust the chain, but it seems a bit louder and less smooth. The teeth on the rear are not perfect but don't have that crooked pointy look that really worn ones have. Does anyone know what brand of chain is sold by Procycle-I may order the chain and sprocket set they sell. Thanks for the help!

Share this post


Link to post
Share on other sites

Backfiring is a lean condition inherent in the BST. The stock muffler hides it, any aftermarket is going to pop some on deceleration. If you try to richen it up, your gas mileage will go to heck.

Stolen from another, smarter than me:

Two or three posters yesterday asked about DR’s backfiring, probably on deceleration. Didn’t see an answer, so here’s mine.

Most street bikes with carburetors have a decel circuit built into the carb to meter in a bit of fuel on closed throttle, to prevent or greatly reduce backfiring on deceleration. My KLR has this, as has every pure street bike I’ve owned. The simpler DR carb does not have this circuit, hence you will be hearing more backfiring than other bikes you may own or have owned.

This is not a problem, rather it is simply a characteristic.

My chain went 21,700 with two or three adjustments. I got home from a ride last week and my chain was loose, so I adjusted it. Rode another 150 miles, got home and it was real loose. 22,000; mostly street, short shifting, easy miles; lubed after every 120-150 mile day rides. I'm putting on a new chain and sprockets today.

Edit: NordieBoy, you're right, I missed this: "but when riding the decel popping is bordering on obnoxious."

Edited by Craig in Denver

Share this post


Link to post
Share on other sites
Backfiring is a lean condition inherent in the BST. The stock muffler hides it, any aftermarket is going to pop some on deceleration. If you try to richen it up, your gas mileage will go to heck.

But in this case it's the difference in packing that's caused the sound increase.

Same pipe before and after.

Share this post


Link to post
Share on other sites

You mentioned the exhaust is quieter at idle now... does the same apply throughout the RPM range while riding? If so, maybe its not that the decel pop is louder than it used to be. Maybe its just that the normal exhaust tone is quieter, making the decel pop more noticeable and louder by comparison.

Share this post


Link to post
Share on other sites

I've heard of people richening up the A/F mixture to help with decel pop. Milage may suffer.

Share this post


Link to post
Share on other sites

Thanks for the feedback everyone. Come to think of it, it's a little bit quieter when riding at normal rpms, but this morning I noticed it even backfired (popped) when I was warming it up at idle and cut the choke down. It's never done that before. I may try adjusting the idle mixture screw-don't know if this will help. I'll also check for an intake leak and cracked vacuum caps on the carb.

Share this post


Link to post
Share on other sites

There is a chain measurement specification in the manual. Replace it if its getting close. My 09 has almost 17K and its still good but I'm not taking any chances. It's going at 20k needed or not.

Share this post


Link to post
Share on other sites

Did you reseal the joints on the muffler when you packed it? The inlet cap must be sealed with high temp silicone or air will be drawn into the muffler causing decel popping. Anyplace between the exhaust port and the exit of the silencer where air can get into the muffler system will cause decel popping. Make sure your mid pipe gasket (if the Procircuit pipe uses one) is not leaking or you have sealed the head pipe to mid pipe connection with high temp RTV like you do on the FMF pipes.

Share this post


Link to post
Share on other sites

Just a thought but repacking it may have increased the flow just enough to make a noticeable difference if you were already running on the lean side (popping is typically indicative of a lean condition). Usually a little carb tweaking is all it takes provided there aren't bigger issues (exhaust/intake leaks)....if I remember correctly it's either move the needle up one or step up a main jet size depending on how lean it is. Also if the silencer was in bad shape when you put the DJ kit in it may make the tuning difference a little more significant.

Share this post


Link to post
Share on other sites

RIder4Life-I think you may be correct because I adjusted the idle mixture richer and immediately the engine idled smoother. I may change the main jet back up to a 170-I had lowered it to 160. First I need to ride more to see if the idle adjustment has helped.

Share this post


Link to post
Share on other sites

Let me know how that works for you. Mine pops quite a bit too. I was at a 170 main and it felt a tad better at mid range but not much at all so I went back to 160 cause the 170 was killing me on gas. I have a heavy hand

Share this post


Link to post
Share on other sites

Here's an update on my DR. On a recent 800 mile trip in early July that went from sea-level to over 10,000 feet, my bike started to run rough at higher altitudes. When not fully warmed up it surged badly and would not idle, and it was not a choke problem. When I got home I pulled the plugs and found some black soot, so I pulled the carb and went through it a bit.I decided to lean it out a little by lowering the needle to the 3rd clip but I used one washer under it. The washer seemed to improve the slide action a little . With this leaner set-up, the bike runs better and I picked up a couple of mpg's (47 vs 45 average). This post was initially about decel popping, but I am not having problems with this anymore since I adjusted the mixture screw and tightened the carb clamps. My set-up is a bit leaner than the Dynojet recommendations that came with my jet kit but I guess variations are normal. If I have any more issues with this carb I may ditch it and get a a TM40:thumbsup:

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×