426f backfire?

i just picked up an 01 426 fr pretty cheap but it has some problems, it starts right up first kick but backfires quite a bit, it has a white bros e series pipe on it and i was thinking it could have the wrong jetting, or the timing could be off, any advice?

i just went out and started it again, its not a backfire, its more of just a loud popping on the decel, when i gas it, it sounds fine but it wont idle at all and it pops alot on the decel

Are you sure it's a back fire and not a miss-fire? A true back fire comes back thru the intake and can start your air filter on fire.

If you leave the hot start button in the on position you can have a really lean condition and it will pop out the tail pipe quite obnoxiously.

Are you familiar with the hot-start on an '01? It's the red button on the left side of the carb. The black one behind it is the choke.

An aftermarket pipe such as the one you listed may give you a lean condition when 1/2 to full throttle, but not on idle.

If you are still having pretty bad pops, just clean the carb real good. Review your jets with your manual. You main may be one or 2 sizes larger due to the aftermarket exhaust, may find your needle down a position or 2 also.

i just picked up an 01 426 fr pretty cheap but it has some problems, it starts right up first kick but backfires quite a bit, it has a white bros e series pipe on it and i was thinking it could have the wrong jetting, or the timing could be off, any advice?


i may sound like a complete noob but lol my bike dont have a hot start button, here is the pic of my carb


i know where the red hot start is supposed to be but i dont know where it is on here, also im not really sure what the black knob is at the bottom of the carb, fuel/idle? idk

The small tab visible on the frame at the right of the picture used to mount the hot start on your bike. The 400 had an external hot start system, which was essentially an air valve and hose that ran from the clean side of the air boot, through the valve, and to the cylinder head to a port leading into the intake. If the port is missing, you may have a 426 head.

The bike also appears to be missing the upper engine mounts, from the tab on the back of the head to the frame backbone.

Absent the hot start, you might need to very slightly open and hold steadty the throttle when hot starting.

the bike is a 426, so there is no hot start? or is it missing, also i will definitely check out that missing engine mount

I would suggest you read your VIN code off of the frame. The carb in the picture is from a 400, by the looks of it. It should have a code stamped on its left side, and a 426 carb should say "5JG...". "5BE..." is a 400. The 426 carb has a hot start knob on the side of the carb.

The 10th character of the VIN is the year model:

  • W=1998
  • X=1999
  • Y=2000
  • 1=2001
  • 2=2002

yeah you are right, the code on the carb read 5BE so do you think that the bike is a 400 with a 426 head? cause by looking at it the head does look a lot newer than the block

The VIN code on the frame will tell you more about the bike.

If you look at the left front corner of the cylinder, just above the crankcases, it often has the engine size cast into it.

wow it definitely is a 400...im ticked cause the guy told me it was an 01 426f, how is the power comparison between the two? cause im thinkin about tellin this knuckle head to pound sand and take his bike back

There is about a 2HP difference in the engine performance. About a 15 pound difference in weight, (the 400 is heavier). And about an $800 difference in value. Personally, I'd tell him to eat it. Have you checked the VIN number?

yeah...the VIN is ground off and spray painted over =)) so i cant figure out what i got even if i wanted to, i also got the number off the block and called yamaha to see if they could give me a model number or anything, they cant because its supposedly 10 or more years old. what do you think i should do?

I had a YZ400 Stolen several years back that had a WB E-Series pipe on it. Any chance you could send me the engine block numbers from it? Maybe we can both get this guy. I know it is a long shot, but worth checking into. Thanks, PM me if you think this is possible for you.


Maybe a few more pictures as well if you don't mind.

umm could you send them to me? no offense but anyone could say yeah thats my bike after i give them the ID numbers lol

No offense taken, I would be glad to send the numbers. I'll have to get them though. I put them in a safe deposit box a while back. Kind of gave up on it, but this is worth checking to me. I'll get you the numbers in the next day or so. Thanks for checking, I appreciate it. Would you mind posting more pictures of the bike for me? Or e-mail them to jbrooks26atcoxdotnet? Thanks.


yeah...the VIN is ground off and spray painted over =))
That's a felony right there in many states. I'd get the police involved.

yeah i did get the police involved, he said to try and get the title or vin any way i can, because the bike may be stolen, so before i do anything they need to run it just to make sure its not stolen or is flagged in any way, but the guy i bought it from has nothing, he supposedly didnt even know the bike was a 400, or have any clue the vin was scraped off and painted over

he brooks my email is copley101@gmail.com, ill put some more pics on when i get home but heres a couple


If they really wanted anything to do with it, the police could raise the VIN number, regardless of the fact that it's been ground off. Stamping leaves an impression in the metal that goes far deeper the the surface.

Since they're not apparently interested, I'd go back to the seller and tell him that it isn't what it was represented to be when you bought it, you don't want it, and to undo the deal. Or, at the least, refund a few hundred dollars.

Bear in mind what it's going to be like for you to sell it.

thanks man i really appreciate your advice, im going to get me cash back fr the bike...who knows it probably been stolen

OK, I will try to get the information this afternoon and send it to your e-mail. I appreciate you checking anyway. If you get the guy to take it back, please record any numbers that you can and keep contact information for him until I can get you this information. Thanks again.


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