Fuel Mixture Screw Magic...

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.

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.

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.

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.

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

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.

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