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Backfiring when decelerating and then accelerating

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Sucram24

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When I roll the throttle down to decelerate and then roll back on quickly to accelerate I get a backfire sometimes. It is not really loud but is definitively noticeable. What should I check. I bought this bike used. It has 14K on it now and is totally stock. I think the original owner had a aftermarket slip on pipe on it before and put the stock pipe back on to sell it. There was no PC or other mods done to the bike. Any Ideas? Thanks Guys!
 
it's normal.

just to confirm, it happens when you are in the high rpm region, say >7k rpm when you start to do a quick deceleration?
 
This is normal, and most noticeable with the stock pipe when the previous owner has gutted the CAT in the header pipe. Otherwise you probably wouldn't notice it at all.

My mate just bought a used FZ1N with stock pipe and lo and behold we can also hear it backfire now and again - gutted CAT!

:noworries:
 
It's not actually a backfire, and with a aftermarket can it's usually quite noticeable but just to make sure the PO did the recoup of the original muffler correctly, I'd check the EXUP vavle and motor to make sure they are working properly. If an aftermarket can was put on once, it's a fact that the EXUP was inop and the cables to the motor more than likely removed. It has been a guesssing game in the past for some riders who did this to get the cables back in position correctly so the actual EXUP valve works as it's been designed. A quick check would be my advice.
 
I took a look this morning and yes it looks like the cables are missing. Does anyone have a pic that show what it should look like? Will it hurt anything to run it the way it is? What would the benefit of hooking it all back up be? I have read that that issue shows up even with the exup valve operating.

Thanks for all the input.
 
Shouldn't hurt, as the EXUP valve only quietens the exhaust tone at low to medium rpm for compliance IMO. Looking inside the pipe you will find the valve / flap is fully open without the cables connected. As with an aftermarket pipe, it is not required.

Have a look at Copperdawg's aftermarket slip-on fitment insructions for photos / videos of the EXUP removal and reverse if you're keen to refit it.

If it was me, I'd rather fit a slip-on...:sinister:
 
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Sucram24 said:
When I roll the throttle down to decelerate and then roll back on quickly to accelerate I get a backfire sometimes. It is not really loud but is definitively noticeable. What should I check. I bought this bike used. It has 14K on it now and is totally stock. I think the original owner had a aftermarket slip on pipe on it before and put the stock pipe back on to sell it. There was no PC or other mods done to the bike. Any Ideas? Thanks Guys!
Click to expand...

This is normal behavior. Fuel is cut during deceleration and as throttle is reapplied there is a slightly delayed "bang" as the return to power occurs. Search this and the other site for Ivan's FCE (fuel cut eliminator). It gets rid of the fuel cut related throttle snatch and would get rid of your "backfire" as well. . .
As already mentioned, the GenII's exup is primarily a noise control device and with no cables attached would default to the free flow / open position.
 
I don't consider this normal if the bike really is stock. My initial reaction is that the EXUP is not connected AND, I'm heavily betting that the CAT was gutted. Any takers?
 
FZ1inNH said:
I don't consider this normal if the bike really is stock. My initial reaction is that the EXUP is not connected AND, I'm heavily betting that the CAT was gutted. Any takers?
Click to expand...

i bet that's it too. because if it's hooked up correctly, and the cat isn't gutted, then there should be no backfiring what so ever. but it sounds like the exup was never recconected. maybe the previous owner lost the cables or something, or just forgot/ didn't feel like hooking them back up.
 
FZ1inNH said:
I don't consider this normal if the bike really is stock. My initial reaction is that the EXUP is not connected AND, I'm heavily betting that the CAT was gutted. Any takers?
Click to expand...

the EXUP valve will be open when you pull above a certain rpm, isn't it? hence the backfiring..

i am running a slip-on, with the cat still 'meowing' inside, and i do get backfire popping whenever i do a high rpm off throttle..
 
aRcHeR said:
the EXUP valve will be open when you pull above a certain rpm, isn't it? hence the backfiring..

i am running a slip-on, with the cat still 'meowing' inside, and i do get backfire popping whenever i do a high rpm off throttle..
Click to expand...

i am just saying, that a stock fz-1 with out the cat gutted shouldn't be backfiring if everything is hooked up correctly. mine didn't and i haven't heard of anyones doing if before. it is usually backfiring or popping when an aftermarket pipe is introduced to the bike. so that being said, i am with eric, and going to say that something isn't hooked up at all, or isn't hooked up correctly.

i'm no mechanic. very far from it. just going off what i have experienced, so i very well could be wrong
 
aRcHeR said:
the EXUP valve will be open when you pull above a certain rpm, isn't it? hence the backfiring..

i am running a slip-on, with the cat still 'meowing' inside, and i do get backfire popping whenever i do a high rpm off throttle..
Click to expand...

The EXUP will alleviate some of these but not all. And, yes, with the CAT in or out, a slip-on will pop on high RPMs without a tune, PC and/or FCE and no AIS blockoff. Mine pops a little with no AIS, slip-on and a CAT but it doesn't backfire at all.

With the stock exhaust, you shouldn't hear hardly even a pop. Hence, no EXUP and/or no CAT in the header. Who knows, the PO could have even punched out the stock can with the 1" drill bit too. ;)
 
Backfire? Just a word. What he is describing as I have already mentioned, sounds like the occasional "bang" that is produced on a completely stock bike when returning to power after deceleration. I could duplicate this reliably on my 06 before modifications. This has been described in any number of theads. . . .On the GenII an exup valve (that isn't stuck) will be fully open if it doesn't have cables connected. It should have no effect on high RPM behaviors . . . .
 
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On an '06 it is more pronounced due to the fuel cutoff issue. '07 and beyond, Yamaha reduced the effects. On my '09 and on my wife's current '07, with the EXUP and stock can in place and the cat's all meowing, it doesn't backfire at all. I cannot duplicate this on my machine now but I can on my wife's bike. It just doesn't do this at all.
 
I agree, with a box stock exhaust setup (EXUP intact and working, cat's in place) there is absolutely no backfire heard or felt when abrubtly cutting the throttle at any rpm. That's on my 2009 model.
 
The EXUP cables are not installed. Not sure if the CAT is gutted. I will pull the pipe and check this weekend. I think backfire was not the best way to describe this as it is not a very load bang. It is more of a pop. In any case it does not seem to effect performance. My question is will it hurt anything to continue to ride? Thanks for all the info.

Sent from my ADR6300 using Tapatalk
 
Sucram24 said:
The EXUP cables are not installed. Not sure if the CAT is gutted. I will pull the pipe and check this weekend. I think backfire was not the best way to describe this as it is not a very load bang. It is more of a pop. In any case it does not seem to effect performance. My question is will it hurt anything to continue to ride? Thanks for all the info.

Sent from my ADR6300 using Tapatalk
Click to expand...

Nope, this isn't hurting anything at all. If anything, you're being more responsible to the environment by having your exhaust burn up more excess fuel than those of us who chose to remove the AIS and/or gut the CAT. ;)
 
Perhaps I'm picking at nits here but the pop is most likely in the intake tract and as a result of the delayed shot of fuel into the hot / dryed out intake tract (fuel has been cut off during decel). The popping associated with the AIS system burning excess fuel in the exhaust occurs in a bit different circumstances. Regardless, what you describe is actually normal on many forum member's bikes and shouldn't cause concern.

Here's a thread which may be of interest . . . .

http://www.yamahafz1oa.com/forum/showthread.php?t=113415&highlight=backfiring
 
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