What else can I do?! BACKFIRE

A

andyw8705

Registered
Ok so I had a completely stock 2000 busa with about 8000 miles on it and I decide to change the exhaust on it and give her a good tune up...so I changed the spark plugs, did the pair valve mod,,marble mod, put a k&n filter, flushed the coolant system, and since I didnt really have the money, I bought some headers from an 06 busa and put some stubby tips on to replace the awful midpipes and cans of the 99 and 00 busa's. Well I ran into a problem, it backfired like crazy, mostly during decel and constant throttle anywhere between 2500-4000 rpm. I took it ato the dealer to have it put on the dyno and they said those pipes are too difficult to map out so they just tuned the ECU i guess it was. That didnt help so i decided to tinker with the PC3USB by myself. After tinkering the power commander for days i finally gave up and bought a yosh r22 full system, and still backfires, not only that but im shootin flames and there is white smoke comin off the pipe...im running a stock map and i plan to try a few different ones today...DOES ANYONE KNOW WHAT IS CAUSING THIS BACKFIRE?!?! did i mess up putting the plugs in?! what the hell is goin on here?!?! it didnt backfire before
 
i tried goin to the website but nothing seemed to match, unless im lookin in the wrong spot...only tuner shop is about 3 hours away sadly
 
I agree with a real tuner shop, other thing is check for air leaks in your block off plates or header connections.

Remember you are running stubbys so that may be helping the fuel meet the air.
 
Dumb question are you sure you put your plugs in right? check your firing order if your having the same issue with both sets of pipes ...i know sounds stupid but being in a hurry to hear your new pipes .... just a thought i would check there first since your questioned it in your original post you could have 2 of your wires switched causing it to fire out of order or maybe one of your caps are not seated properly causing it to fire intermittantly hence the backfire from fuel build up? just my .02 on this subject
 
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Camaro could be right,,but if you have 2 wires wong,,it will backfire like crazy in all the rpm levels,,,if it is not,,,,It IMO that the upper posta are correct,,shory pipes can alow cold air in to the valves[backpressure] and backfire badly,,exspecially when you let off the throttle,,,,,,does id do it while throttleing up? at all rpms/ just when you let off of it? or just at a certain rpm? I believe , only from what little info,,,,its in your exhaust,,you[as mentioned above] I believe you have a leak,,,and as for maps,,,go to LIke said above,,,to powercommander/dyno jet,, and down load thier softwware and all the maps for your bike,,,there is a map for that yosh pipe in their archives[sp],,,but remember this ,,,not all bikes will rspomd to the same map,,fine tuneing can be done by a trained well gifted tech,,,by a dyno is the way to go,,,you can tweak it and get it vvery close if your gifted,,,but a dyno is sweet and takes the guess work out,,,,BTW,,,check your header to head connects amd make sure your not leaking there as well,,suspicion arise's because you had the same problem with the other pipe and now you have a brand new yosh,,for which I assume the model you have has a longer pipe and not a shorty,,,,,and i do agree with the upper posts,,,some dealers,,really suck at tunes,,,if your near or schnitz [ryan] anyone here who dynos,,let them chime in,,,,there are some guys here who now how to dynotune
 
im not a bike tech so i was just putting in my .02 but i am a tech and i would start with the obvious since you stated it does it in both acel ,constant and decel i dont believe during acceleration it would back fire out the exhaust unless you have a spark issue so IMO i would start with the easiest to check and work my way to the hard stuff IE. plugs wires and work my way to my mapping im not tryin to step on any toes and say anyone is wrong in their ideas but if it was my bike i would check the easy stuff and rule it out first before i went onto stuff like mapping also i know it would suck but you could undo your mods and see where the problem lies ???
 
thanks for all the tips guys i really apprecaite it...to clarify the backfire usually happens on constant decel and constant throttle around 2500-4000rpms...i went to the pc website but the only map i see for my set up is only available for the PC2 unit, it would seem that the plugs would be a easy culprit because it is the only mod besides the new filter that has been through the stubby system and the yosh system but it just seems weird it only backfires at certain times, seems if the plugs were the issue it would be a problem up and down the rpms
 
One thing else,,I have found,,,that when I do a few mods or swap out something or a tune,,I do one thing at a time,,then check my work,,listen to the vehicle and start on the next fix,,,,that will diffently help with the process of ilimination,,,,,doing alot of different things at once ,can lead to this very issue,,,But check everything and retrace your steps,,,after re=reading your post,,,,,as camero said,,,,look at the plug wires to make sure you didnt cross 2 of them,,,I know thes bike are simular[busa],,,but the last time I swapped out my plugs and had to unplug the coilpaks from the harness,,there is not enough room for mine to reach to another plug to make that mistake,,,you would really have to stretch it far and would be noticeable on my bike,,,also pull the plugs to see if you have a dead one,,,but ive had a plug die on me and it missed but didnt backfie like what your describing,,,,,,,,,,,,,Im glad my harness is short so that I cant cross them.,,,,,,also a buddy called me up and told me that one of his coilpaks was not snapped all the way down onto the plug,,,this could cause a miss,,,,but your talking backfire,,,,check everything [fireing order,and bike leaks and vacum lines,,,,mapping could be an issue,,,,,,,,,,,backfires ussually denote fire/timeing and ehaust/vacum problems issues
 
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Did you make sure to gap the plugs? Are you sure the pair mod was sealed properly? I had a small gap in my seal when I did the air box mod, and it caused backfire on deceleration. My bike has the shorty pipes too.
 
FIGURED IT OUT!!!!!! it turns out that the fuel line from the petcock was kinked so I thought maybe this is the issue. Unbolted the tank bolts and piled some tshirts to where the tank was raised enough to take the kink out and sure enough, took it for a half hour ride and not one pop!!! this makes sense when you take into account the fact that it was only popping at constant throttle at low rpms and decel...at heavy throttle, the fuel demand was enough to overcome the kink but at constant throttle and decel the pressure wasnt enough to overcome the kink causing a very lean mixture...I HOPE THIS HELPS SOME OF THE OTHER PPL THAT ARE HAVING BACKFIRE PROBLEMS, and ps...the kink was very very small, I never thought it would have been enough to cause an issue
 
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