Back Fire On Decel

[Cadillac94Pimpin]

Just got my bike back from the dealer 2 1/2 months later. (2nd gear disease). I had to pay for the repair but they did discount it though. I had all gears undercut and it shifts so solid its not even funny. Much better then stock. Anyways I am getting this weird back fire after I got my bike back. I have stock unmodified exhaust and no performance mod's. I will rev it up past 7k and let off the gas and as its coming down as soon as it its 4k it pop's sometimes once some times a few times and it does not matter what gear I am in or how hot or cold the bike is. It always happens at the exact same RPM (4K) I brought it back to the dealer and the mechanic rode it said he didnt notice anything. Then I rode it and it did it. Then they had another guy ride it who heard it faintly.  I asked him if it could be an exhaust leak as I saw a thread with that answer.  He told me it was not an exhaust leak as you would hear it. He said I should run 2 tanks or so of super since the bike has been sitting so long and if it continues after that then bring it back. There does not seem to be any performance issues just this obnoxious back fire. The bike has has 4,000 mles on it and did not do this before I brought it in. What could it be?

?

 

[Revvv]

I'm not sure what the problem is, but I am sure it's something the shop did when re-installing the engine.
It's something minor. This shop may not want to own up to its mistakes so you may have to take it somewhere else for a second opinion.

Motorcycle dealerships are a pain.

 

[Gunnybusa]

Sounds like an exhaust leak to me.

 

[Professor]

I vote exhaust leak as well.

 

[bigoltool]

Exhaust gaskets are not that tough to check. Make em do it!

 

[stlbusarider]

Try buying a cheap stethescope from a car parts store and ck the exhaust yourself. Specifically at the cylinder head.

 

[GPW]

(Gunnybusa @ Jul. 31 2007,08:27) Sounds like an exhaust leak to me.

+1

 

[BusaWhipped]

If its an exhaust leak with unmodified cans, shouldn't you be able to hold your hands over both exhaust outlets and listen for it blowing out somewhere else?

 

[Charlesbusa]

Another idea is to put it on a dyno with a fuel/air sensor. That way you'll know if its too rich or lean...

 

[Cadillac94Pimpin]

Ok, Well it is still happening. Im so sick of the stupid dealers out there. Im probably going to bring it back. I really dont know how to check for exhaust leaks nor do I really feel like it especillay after I paid all that money for someone else to do it. One question, exhaust is suposed to come out of the drain holes on the can right? I also noticed that its more noticable IE Louder pop when I rev it up higher in a higher gear and let it wind down. I am going to do the marble mod for sh*ts and giggles to rule out the pair. I think that is as far as I am going to go.

 

[Cadillac94Pimpin]

Marble mod fixed it!!!!!! I did it without the marble though. I used two rubber end caps. My exhaust is stock why did this happen?

 

[Charlesbusa]

The PAIR valve injects fresh air to burn off unspent fuel and gasses for emissions.

The marble mod dissables the Pair valve.

The problem may be that you are still running rich, since the marble mod just covers up the problem. Keep an eye on your spark pulgs if you can't afford to have the fuel/air ratio checked on a dyno.

 

[Cadillac94Pimpin]

Not to sound stupid but what would make the bike run rich if it is stock? I did notice in the morning the right can puts out a whole lot more vapor then the left. I do not know if that has anything to do with it, just throwing it out there.

 

[Bokey]

Does the bike hesitate between 3k-4k RPMs with the throttle cracked? As you're in slow traffic?

 

[Cadillac94Pimpin]

It does not seem to hesitate at all. It seems to run great. I do run the **** out of my bike but my gas mpg is indicatiing 25 mpg. I dont think it has ever been that low before. It started out at 40 when I first got my bike then went down to 30 as I started to get used to it

 

[Bokey]

Check the clamps on the throttle bodies. I had to tighten the lower ones with the long screwdriver thru the hole in the frame.

 

[robvas]

My stock 2000 does this. I open it up until 6-7,000 rpm, close the throttle, and I swear the second the tach touches 5,000 rpm....KA POW!

A nasty, loud back fire. At night it shoots a blue/orange flame out of the pipe, very cool!

It does it every time in second but I have gotten it to do it in other gears.

If you time it right, you can pull up next to your buddies, and point your hand at them like a gun...it's funny at least the first 20-30 times

 

[Over_Easy]

Replace the pair valve w/ block off plates and caps.

 

[kd185]

its definitely an exhaust leak sucking oxygen into the system on a closed throttle situation causing a lean condition

 

[Lesbusa]

It's the PAIR valve beginning to go bad. My bike did the same thing. Something happens to the valve as it starts to age and the bike spits flames and backfires going from 5K down to 4k.