2004 Yamaha YZF 450 spitting fire out exhaust

8 replies to this topic
  • jsmith72

Posted February 09, 2009 - 11:12 PM


Ok, I sprayed carburator cleaner in the carb while it sat in the garage (to install new warm start cable) and when I went to ride it, it was poping(not quite a back fire) and is shooting flames out the exhaust when this happends.(when in neutral only while reving it up) I have now cleaned the carburator 3 times and it still does the same thing. I was told that the pilot Jet would cause this but I have gone through the carbeorator and it still runs the same, poping ect....Does anyone have any input on why. The spark plug is clean showing the bike is running lean and in less the 5 minutes the exaust gets red hot, which it has never done either. Any suggestions on what it might be. It is not the warm start, it works fine and leans the bike out when you pull it while it is running like it would normally.

  • rufusz

Posted February 10, 2009 - 02:03 AM


My 426 did this when the engine got false air, one of the clamps between the engine and the carburetor was loose

  • yamaha6j

Posted February 10, 2009 - 05:48 PM


Is it the stock pipe or after market ?

  • YZThumper07

Posted February 10, 2009 - 06:36 PM


Sounds like you're running Super Lean..like rufusz said, it could be a loose boot somewhere between your air box and the engine.....Also check really close to see if your head pipe is secure to the head and go all around it and check for cracks or holes.....I know you said it wasn't the hot start..but double check to make sure your hot start isn't being slightly held open under normal operation...any of that could be causes for pulling in extra air and causing you to run Lean

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • jsmith72

Posted February 13, 2009 - 05:44 PM


the hole bike is stalk including the exhaust

  • jsmith72

Posted February 13, 2009 - 05:50 PM


thanks for all the input guys, everything looks tite (clamp between carb and motor), I will double check the warm start, I cleaned the air ports in the carb as well and could blow air through everything, could those little vent holes also cause the poping......also, by looking at the spark plug (clean as a whisle) it is defanatley running lean, and it only takes about 3 minutes for the exaust pipe at the bend from the motor to get glowing red hot, and the bike seems to run hot unlike before I last road it.....since I screwed it up some how.


Posted February 13, 2009 - 10:22 PM


My 426 did this when the engine got false air, one of the clamps between the engine and the carburetor was loose

if the carb had an air leak you would get an irratic idle or a very high idle. check the plundger on the hot start and make sure its not stuck. (i'm saying this cuz you said you replaced the cable) does the plundger move freely and is it seating all the way down? how does the bike run when its in gear? i've owned two yz450s so far and they both popped on decel with a lean pilot and or airscrew. i use a 48 pilot with a filter and slip on, but even when the bike was stock it ran better with a 48.

  • grayracer513

Posted February 14, 2009 - 08:46 AM


the hole bike is stalk including the exhaust

You mean the whole bike is stock. Renner is probably onto something here. Think about it. It did not do this before you messed with the hot start, and now it does. It would be the first place I looked.

Be sure the cable has free play in it at the lever, that it moves freely, and that it returns positively under its own spring pressure.

  • jsmith72

Posted February 14, 2009 - 11:59 AM


It is hard to see if the plunger is all the way down, I guess I can take off the carb have the warm start hooked up, take the top of the carb off so I can see if it is seating all the way. As far as the cable goes there is free play telling me it is sitting as far down as possible. The spring is new also(hopfully yamaha gave me the right spring(looks the same) and it is making the plunger seat all the way down when there is play in the lever.....hard to say, I will see if I can see it through the top of the carb. When I am in gear and riding (on the gas) it, it seems to run great until I back off the throttle coming to stop, it will want to pop and die...so on the gas runs good, otherwise will pop and die .If I pull the choke out, ride it and come to a stop, it will idle (higher idle) but if I take the choke off, it will die. and yes it is bone stalk, never changed jetting and has always ran good in the valley/higher altitudes like sand mountain or truckee ca.

Related Content

WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

YZ450F 03 Sparks driving me crazy by SirAttard

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

Is the 2016 GYTR Yamaha YZ450F too fast? by Fryboy

Dirt Bike   Special Interest Forums   Pro Racing
  • * - - - -
  • Hot  241 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.