why does my yz450f give pops on deceleration

25 replies to this topic
  • bzakk

Posted October 12, 2004 - 12:52 PM


I just bought an 05' 450f and when I get the rpm's up then let off of the gas I get little pops out of the pipe only if I stay in gear and let the motor wind down, why is that? :cry:

  • brown77

Posted October 12, 2004 - 12:55 PM


Its running lean

  • bluerider450

Posted October 12, 2004 - 01:05 PM


my of does that to sometimes bikes come from the factory running rich or lean just probley have to adjust the pilot screw in the carb a little not sure how to do it i still have to find someone to richin mine up for me a little bit
or get some advice fromanyone on here who knows how to do it

  • bzakk

Posted October 12, 2004 - 01:12 PM


That isn't going to hurt anything is it? Will that affect power?

  • bluerider450

Posted October 12, 2004 - 01:14 PM


the only thing i know of that it will do is your more likely to foul out a plug

  • mxmhero

Posted October 12, 2004 - 02:51 PM


HMMM mine does that also , i just bought a leftover 04, makes me nerves when u say it could be lean, i have to check into this.

  • Fastest1

Posted October 12, 2004 - 02:51 PM


It wont hurt anything but it is too easy to fix. Look under the front of the carburetors bowl, there is a small hole with a screw inside (fuel screw). You can take a small flathead screwdriver bit and fit it in there. Clockwise for more fuel, counterclockwise for less fuel. You will need to more fuel to eliminate or lessen the popping. You do want a very small amount of popping on deceleration for the best throttle response. Eventually I would suggest an extended fuel screw for the FCR carb. It will make this adjustment able to be done with no tools. It gets hot around there trying to do it with just a screwdriver bit. You should really adjust it every ride for the best performance.

  • bushy

Posted October 12, 2004 - 03:46 PM


You have it backwards.

If you are looking up at the screw its tighten for less fuel and loosen for more fuel. Do not go greater then 3 turns out, if you have to you should replace your pilot jet one size bigger.

  • bluerider450

Posted October 12, 2004 - 03:53 PM


so then loosen it to let more fuel and more fuel mean richer right?

  • YZ250F_Rider

Posted October 12, 2004 - 04:10 PM


turn it a 1/4 turn CCW at a time. It shouldnt take more than a 1/2 turn before it starts behaving.

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  • bluerider450

Posted October 12, 2004 - 04:15 PM


yeah ill try that next time i have it out

  • Baycrosser

Posted October 12, 2004 - 08:42 PM


Thx Guys, good advice. i got the same prob here.
hopefully the european version got that fuel screw too :cry: :cry:

  • YZRIDER1127

Posted October 12, 2004 - 09:38 PM


From the dealer mine came .5 turns out i went another 1.5 out and it kept the bike from stalling...still gets a little backfire but it runs great.

  • Fastest1

Posted October 12, 2004 - 10:26 PM


Yeah, I just realized I wrote that, Sorry it is vice versa

  • bluerider450

Posted October 13, 2004 - 06:25 AM


the screw is the same on anything else right left to loosen and right to tighten?

  • YZ250F_Rider

Posted October 13, 2004 - 06:49 AM



lefty lucy, righty tighty. turn it left to richen and reduce the backfiring.

  • jerryls

Posted October 13, 2004 - 09:23 AM


Also check the gasket between your head pipe and the muffler. If it's a loose fit, it can cause backfiring. You'll be able to feel air escaping at the junction when the bike is running. Use some high temp RTV on the gasket if that's the case.

  • bzakk

Posted October 13, 2004 - 09:42 AM


I am going to turn the fuel screw all the way to the right then give it 2 full turns to the left and see which way to turn from there thanks guys :cry:

  • brown77

Posted October 13, 2004 - 09:57 AM


n/p :cry:

  • grayracer513

Posted October 13, 2004 - 10:01 AM


the screw is the same on anything else right left to loosen and right to tighten?

It is if it's a FUEL screw. Almost all off road four strokes built in the last 6 years at least have idle FUEL screws. Two strokes and older bikes have idle AIR screws, which work the opposite way rich to lean. The give-away is usually the location of the screw. If it's in the float bowl, it's fuel. If it's near the mouth of the carb, it's air.

Yours is clockwise/right/tighter=leaner and vice-versa.

Before you adjust your fuel screw to fix this, be sure that the clamp at the mid-pipe is tight, and check the flange at the header/head joint, too. An exhuast air leak will also cause this. If the leak is small, you can still supress it with a leaner idle, but if you do that, your idle will actually be too rich.

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