Backfiring on decceleration

[shredex]

i went on a ride today with one of my friends Justin. He has a 01 R1 with a Aftermarket Wolf undertail conversion exhaust.
his bike just pops alot on decceleration..no flames though.

i wanted to say a leak in the exhaust, but when I checked over it, I couldnt find a leak.
so next thing is I think maybe its out of sync, but if it wasnt in sync, wouldnt it not be as powerful as it is?
hes bike is super powerful and blows by mine like im standing still.
I saw him playing with the throttle in 3rd with no clutch and his front tire was just hovering off the ground .

i was wondering if anything else could cause the popping. to rich?
im gonna tear apart his carbs here soon so its gonna get a good cleaning and tune up.

[95FZR600]

Oh no! Dont work on his carbs....it wont run at all when he gets them back! LOL2

Sounds like it is a but rich.

[ragedigital]

Generally it is from too much gas... the gas that doesn't burn ends up burning in the exhaust causing the popping noise.

[95FZR600]

Maybe he should run a higher octane? Burn slower?

[ragedigital]

It happens on carbed bikes more than FI ones. He just might need to adjust the carbs. Maybe he's got an issue with too large of a main jet or something worn out that is "richening" the circuit.

[shredex]

ill give you guys more info when I tear pat the carbs and see if its jetted.

higher octane to fix the richness issue?
do you think this would work for my bike because it still runs rich?

[reelrazor]

They will 'pop' from a lean misfire as well as a rich condition. A lean mix is hard (and slow) to ignite..and under compression is impossible to spread teh flame front.....as the compression drops as the piston moves down-engines like his with lots of valve overlap- will 'afterfire' when the exhaust valve is open. The ignition is happening in the combustion chamber being a stlled kernal of flame and then late leaking into the header. This kinda thing is quite common under engine braking. You'll see it happen on anything with lots of valve overlap...hot rodded small blocks..modded Harleys, and un-rejetted sportbikes. The Harley guys WANT it to happen....and make it so.

You will almost ALWAYS see flames from the tailpipe in the dark when an engine is rich.

It probably has NO carburetion correction for the aftermarket exhaust-and needs it.

fatten up the low speed mix and it will most likely go away.

[ragedigital]

Higher octane will reduce knock and ping, but I don't believe it has any effect on backfiring. Reelrazor can give some better answers I'm sure.

EDIT: How funny is that. I mention Reelrazor's name and he's already posting before I hit submit...

[DEMORAL1ZE]

in cars lean "pops" only happen under accelleration.

[shredex]

It probably has NO carburetion correction for the aftermarket exhaust-and needs it.

fatten up the low speed mix and it will most likely go away.

yea, im thinking when i pull it apart, im gonna find that its not even jetted...


what do you mean when you say "fatten up the low speed mix"?

btw, do the carb'd R1's have a choke? im wondering if My friend doesnt realize he has a choke and he is riding with it still engaged...that causing decceleration pop. thats how i know when iv forgotten to turn my choke off all the way.

[yamaha_george]

They will 'pop' from a lean misfire as well as a rich condition. A lean mix is hard (and slow) to ignite..and under compression is impossible to spread teh flame front.....as the compression drops as the piston moves down-engines like his with lots of valve overlap- will 'afterfire' when the exhaust valve is open. The ignition is happening in the combustion chamber being a stlled kernal of flame and then late leaking into the header. This kinda thing is quite common under engine braking. You'll see it happen on anything with lots of valve overlap...hot rodded small blocks..modded Harleys, and un-rejetted sportbikes. The Harley guys WANT it to happen....and make it so.

You will almost ALWAYS see flames from the tailpipe in the dark when an engine is rich.

It probably has NO carburetion correction for the aftermarket exhaust-and needs it.

fatten up the low speed mix and it will most likely go away.

RR,
+1 on that suggestion of no one re-tuning after adding the aftermarket can !

Fattening the low speed circuit means making it richer.

Talking of after market exhausts I have "inhereted" an oval one after dropping my pals bike (he was on mine) in a diesel spill, seems i still bounce quite well and the leathers & spine brace to the hit apart from a severe adrenalin rush I'm fine.
I cleaned the leathers and re-waxed them and they look used but not crapped out all the seams are fine.