02' YZF426-Popping/Backfiring?

7 replies to this topic
  • yzfit

Posted March 13, 2005 - 09:22 AM


Hi Guys,
02 YZF426, do I give more fuel if it is popping when I let off throttle or does it need more air? It runs strong but does pop when I let off, I do have a Zip Ty adjuster on bowl of carb. Also, hard starting when cold. Thanks!


  • 02YZ426

Posted March 13, 2005 - 09:32 AM


Thants a good question... Mine does the exact same thing. I tried putting new exhaust gaskets and silencer re-pack and that helped a bit. Its always hard to start in the cold, and usually I have to clean, or put a new plug in it to get it runnin. I just put the auto decomp cam in it, and its still the same thing. Once its running, its always takes 1 kick to fire up, but it will pop and bang on the downshift. Im starting to think I will clean the carb and maybe see if the adjustment are right. I wonder if its running too rich?

  • skthom2320

Posted March 13, 2005 - 10:25 AM


Both of you are too lean on the pilot circuit. First thing to do is adjust the fuel screw richer (OUT) about 1/4-1/2 turn at a time. Don't go out more than 2.5 turns total. If you need to go out more than 2.5 turns, put in a larger pilot jet and reset the fuel screw to 1 turn out and tweak it as necessary. Best throttle response on the 426 is when you get some slight popping on deceleration.

  • 02YZ426

Posted March 13, 2005 - 10:40 AM


Is the fuel screw the one that has the plastic knob on it and is there a reccomended amount of turns out that it should be at? or do you just set it as nesesary? I am not that fimiliar with tuning these thumpers, so Ive just left my carb alone. I am great with tuning the 2 strokes but am a dumb a** with these 4strokes when it comes to carburation. My current set up is completly stock on this carb. Where ever that fuel screw is set now is where it was when I got the bike new. Thanks...

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  • Bob_o

Posted March 13, 2005 - 06:12 PM


The screw with the plastic end is the throttle idle adjustment. The fuel screw is on the bottom of the carb and a bit of a pain to adjust until you put something like "zip ty" adjuster in. I had the same problem with my bike and found most of it to be corrected by cleaning the carb. My main problem was that some dirt/grass mix got into my air jets that are on the backside of the intake going into the carb. Mine is still not perfect... but MUCH improved!

  • bzakk

Posted March 13, 2005 - 06:31 PM


You probably won't get rid of the popping completely but my 450 was doing that. I closed the fuel screw then turned it out 2 full turns and fine tuned from there. It depends on your climate. Also check your plug, I also put a better plug with a dual electrode to make sure you are burning as much gas as possible.

  • desertfox89

Posted March 13, 2005 - 07:13 PM


i agree with them i had the same problem with mine and i got imfo i was running alittle lean on the bottem end i turned my pilet screw out .5 out more and it helped. i also think its elevation matters to

  • 02YZ426

Posted March 13, 2005 - 08:21 PM


Im going to try to richen it up a bit, if that doesn's help it, then maybe I will have to double check the jetting. Maybe the stock jetting is just to lean for my area? I will also be cleaning the carb just to make sure its not dirty or anything. What about that TPS? Should I just leave it alone and clean the rest of the carb?

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