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Backfiring during engine braking

djgtekfrmsanjo

djgtekfrmsanjo

New member
Joined
Apr 7, 2008
Location
San Jose/Fremont/Sunnyvale
Moto(s)
2001 250, 98 YZF600R, 01 SV650S, 03 636, 08 CBR 600RR, 2014 Grom
Name
Glenn
I just installed an exhaust and now am
experiencing backfiring noises (popping) from my exhaust when I engine brake. What will happen, if anythig, if i leave it as is? What would be some correcting steps?

Thanks BARF!
 
If you installed a new exhaust (I'm assuming freer flowing) and don't remap the fuel injection (or rejet the carbs) the air/fuel mix is going to be off and can damage the engine. Note I didn't say it WILL damage the engine, only that it can.

What kind of bike and what kind of exhaust?

When I installed the new exhaust on my Aprilia, the recommended fuel map was already installed on the ECU. The dealer simply enabled map2 and I was good to go. If your bike is a Triumph, I believe the dealer can install some updated fuel maps without any issues (for their TORS).

If you have a Japanese bike, you're most likely going to have update the fuel map yourself. You have two basic options:

  1. Buy a Power Commander and download a map from the internet for your bike and exhaust combo. You can usually find these maps for free. These maps are not going to perfect for your bike, but they will get you close and most likely be better than using the stock map with your after market exhaust.
  2. Buy a Power Commander and have your bike dyno tuned. A dyno tuner will create a custom map specifically for your bike.

I'm sure there are BARFers who have your bike and exhaust combo and can point you in a direction for either a map download or a dyno tuner.

Cruise CL for a Power Commander.
 
Check the exhaust for leaks. Sounds like you have an air leak.
 
elskipador said:
in his sig he lists a 2001 sv650.
Click to expand...

What, you expect me to READ these things? I only read sig lines that involve sex, religion or food :x.

Thanks for the info. I believe the 2001 SV650 is carbed? If that's the case sounds like new jets.
 
Its a 01 sv650s and the exhaust is a supertrapp (dispersing). The exhaust is actually tuneable by adding or taking away discs. Would this possibly avoid any need to rejet and correct backfiring if I find the right amount of airflow?

El skipador - i've heard alot of good references about your work. How much would this run me if I want to get everything setup correctly?
 
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You sure hear a lot of that at the track from a lot of bikes presumeably tuned for max performance. Is that too rich?
 
Lovedoc said:
You sure hear a lot of that at the track from a lot of bikes presumeably tuned for max performance. Is that too rich?
Click to expand...
not usually. its actually from running lean & its called an afterburn, not a backfire. when you close the throttle from the upper rpm's the bike goes onto the idle/pilot circuit. this causes the exhaust tract & pipe to heat up really quickly & ignite unspent hydro-carbons in the exhaust. twins, as a breed, tend to like the lower rpm's a little on the rich side so the op could adjust his fuel screws. usually 2.0~2.5 turns out, for a slip-on & stock headers/airfilter will fix it. just remember that it SHOULD pop, @ least a little, on decel. if it doesn't your idle/pilot circuit is to rich.
 
How about this scenario:

Bike doesn't backfire on decell until as soon as you get on gas, then it bangs loudly.
 
djgtekfrmsanjo said:
Its a 01 sv650s and the exhaust is a supertrapp (dispersing). The exhaust is actually tuneable by adding or taking away discs. Would this possibly avoid any need to rejet and correct backfiring if I find the right amount of airflow?

El skipador - i've heard alot of good references about your work. How much would this run me if I want to get everything setup correctly?
Click to expand...

find the air leak

Unless you are running ten plates it is not restricting the flow enough to cause backfiring ( particularly with stock filter)

If you want it jetted correctly, take it to a Factory Pro site and have it dynoed. Otherwise it's going to be close at best.
 
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afm199 said:
find the air leak

Unless you are running ten plates it is not restricting the flow enough to cause backfiring ( particularly with stock filter)

If you want it jetted correctly, take it to a Factory Pro site and have it dynoed. Otherwise it's going to be close at best.
Click to expand...

actually when i add plates, the air flow is less restricted and exhaust is extremely loud. when i take away plates, air flow is more retricted as there is less space for fumes to escape and the exhaust is not as loud. does this mean the less plates I run, the more likely to backfire?
 
Dude. That is why I said "UNLESS YOU ADD TEN PLATES". I used to run Supertrapps with twenty plates and an open end cap. Yes, the more plates you run the leaner the mix is, the louder and more likely to backfire.

how many are you running, what size mains, pilot jets do you have, and what air filter?
 
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