Fuel Mixture Screw Magic...

6 replies to this topic
  • Plusdome

Posted April 25, 2005 - 08:58 PM


I just got a new MSR/Zip-ty external fuel mixture screw I understand what it does but any tips on sea level usage or seat of the pants tuning?? When I say sea level I mean sea level I live in central Virginia and rarely if ever ride above 500 feet above sea level and top out around 3500 feet. I ride a '00 YZ 426 with a White Bros tapered headpipe, E-series can, and a P-38 accelerator pump cover. Any tips from a seasoned user would be appreciated. I also would like to thank everyone who responded to my first thread, this site is amazing and I recommend it to everone I ride with.

  • Fastest1

Posted April 25, 2005 - 10:21 PM


Generally start at about 1&1/2 turns out from seated gently, ride and while decelerating if it pops , it is too lean. Turn the fuel screw out until most if not all popping is gone. It is a fine line so play with it often til you understand it. It will always need adjusting. If it makes no difference in the idle when turning, the pilot is the wrong size. Tinker a lot.

  • ovrrdrive

Posted April 26, 2005 - 12:20 AM



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

Posted April 26, 2005 - 02:47 AM


Fastest 1. I agree good place to start, but note: Some popping on decel is good as it provides better throttle response on accelleration and eliminates most of the bog. Thats one of the differences between the YZ and WR. The WR has a bypass on the AP mod to richen it on decel. Most blokes do the free mod on the WR to make it pop a bit and get the better throttle response. See free mod on the 250 faq site for more info.

  • sirthumpalot

Posted April 26, 2005 - 03:52 AM


My personal advice is, for the most part ignore the sound out the exhaust and tune it until it runs best. If the idle seems to float and not be stable then it's likely lean, turn it out a little (1/4 turn at a time). If it doesn't want to go right when you hit the gas and the idle seems to slow and want to stall then it's likely rich, turn it in 1/4 turn. Once you get in the ball park you can fiddle with it more, but once you start playing with it you'll find the setting you like very quickly. I'm at sea level as well and almost never have to touch it, and when I do it's never more than 1/4 turn.

  • Daz_426_02

Posted April 26, 2005 - 05:32 AM


Just how much popping on de-acceleration is normal/good ?

  • saucebox

Posted April 26, 2005 - 09:00 AM


my personal experience is that i tweak it till you are getting the highest rpm at idle and then when you crack the throttle off idle it dont hesitate. i notice that when my fuel screw is not set right and i crack the throttle off idle it will blurp and die sometimes.. basically i try to eliminate that and it runs great.

Related Content


Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

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

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 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.