The bike is backfiring!!!

[Big Kahuna]

My bike has begun to backfire when I get off the throttle at low speed. Most of the time it kind of grumbles like it's loading up but every once and a while it really let's one a loud pop. It's never done this before and I haven't changed anything in the carbs or the engine.

Any ideas?

[xraycatj]

I just glanced at the manual and got this (word for word):

Afterburn when engine braking is used:
1. lean mixture in slow circuit
2. air cut-off valve malfunction
3. emission control malfunction
-secondary air supply system faulty
-loose, disconnected, or deteriorated hoses of emission control sys.

Backfire or misfire during acceleration:
1. ignition system malfunction (like my dead battery)
2. fuel mixture too lean

[Brent]

Just bring it up to Factory and pay them to tune it..... trust me - my 94F2 did that - it was to have to do with improper carb settings...

[Calkidd]

Lean fuel mixture?

I thought backfireing had to do with excessive fuel in the exhaust pipes igniting?

[66droptop]

Lean fuel mixture?

I thought backfireing had to do with excessive fuel in the exhaust pipes igniting?
I thought popping under load was from lean conditions. Actually, I know this. But I thought that popping under no load (engine braking, et cetera) was from being rich. Not 100% sure on the second part.

[Big Kahuna]

It's strange, You wouldn't notice any problem the way the engine runs. It's still strong and I get no hesitation under throttle or idle.

I had an exhaust leak once, and I could feel it under acceleration, but this backfiring thing is different. It only does it when I release the throttle. If I ride long enough, It will start to do it in between shifts if I'm running it hard and high in the RPMs.

By the way, I jumped on it last night when a guy in a vette tried to get silly when leaving a signal light and I was again reminded how slow those cagers really are. :)

[Brent]

Bad Gas?
Lean?
Exhaust Leak?
All of the above?

[Blademan]

I have always had small backfiring under heavy engine breaking since I put the two bro's jet kit in

[66droptop]

Probably your exhaust bearings. And we all know that means your bike is F-ed up now. Should probably just part it out. Let me try to remember what mods your bike has that I'm interested in... Well there's the clear tail light. I remember that part. You should probably just give it to me for free since I diagnosed your problem and saved you all that time, effort, and money. Oh, and also because not since Steve McQueen has the world seen someone as cool as me. I'll PM you my address so you know where to ship it.

[Brent]

I have always had small backfiring under heavy engine breaking since I put the two bro's jet kit in


Blademan - this could be from an air leak.... in the exhaust system... might want to check that...

If I rememebr they used to package hi-temp silicon for this issue

[Big Kahuna]

Probably your exhaust bearings. And we all know that means your bike is F-ed up now. Should probably just part it out. Let me try to remember what mods your bike has that I'm interested in... Well there's the clear tail light. I remember that part. You should probably just give it to me for free since I diagnosed your problem and saved you all that time, effort, and money. Oh, and also because not since Steve McQueen has the world seen someone as cool as me. I'll PM you my address so you know where to ship it.Damn, it can't be those stupid exhaust bearings... I've replaced those twice already. :confused:

[Big Kahuna]

Okay, I pulled the main hose that goes from the PAIR valve to the airbox. The PAIR valve is suppose to control the flow of fresh air to the intake. When I pulled the hose, nothing changed but when I plugged the hose with my thumb, the backfiring stopped. It seems the PAIR valve must be stuck open thus continuously feeding the intake with too much fresh air.

Mystery solved. I decided to pull the remaining smog crap off as I've already removed the clogged evap canister. I need to find some smog block off plates. I know Two Brothers used to carry them.

How about it Brent, can you hook me up. I know you have connections at Two Brothers.

[66droptop]

Okay, I pulled the main hose that goes from the PAIR valve to the airbox. The PAIR valve is suppose to control the flow of fresh air to the intake. When I pulled the hose, nothing changed but when I plugged the hose with my thumb, the backfiring stopped. It seems the PAIR valve must be stuck open thus continuously feeding the intake with too much fresh air.

Mystery solved. I decided to pull the remaining smog crap off as I've already removed the clogged evap canister. I need to find some smog block off plates. I know Two Brothers used to carry them.

How about it Brent, can you hook me up. I know you have connections at Two Brothers.Wait. We have that crap on 900s? I thought it was just those newfangled bikes with EFI and that mishmash. Stone tools were cutting edge back when the 900 was made.

[Blademan]

Wait. We have that crap on 900s? I thought it was just those newfangled bikes with EFI and that mishmash. Stone tools were cutting edge back when the 900 was made.Never knew either

[Big Kahuna]

It's true!!! Would I lie to you guys? ;)

[Blademan]

OK so he does make a good point . . . !!!!

[wingnut1]

This is a California specific Mod most bikes in the us will not have it....

this is due to Californias emission standards