Question about 2001 Yamaha YZ 426 F
Hi, Brennanhales it should be noted that your performance issues are not electrical ie. faulty charging system, battery condition, and connections etc. If your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetors in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the websites below. Good luck and have nice a day.
Carb tuning on yz250f swivel technique
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Yamaha YZ426F Owner Service Manual
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Posted on Aug 08, 2016
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Posted on Jan 02, 2017
Pull the slide out and then move the clip on the jet needle one notch lower. Also try two notches to see which helps most. This will richen the mix in mid-range.
Pleas rate thia answer. Thanks v222407! :)
Posted on Apr 15, 2009
Hello you have a
1. fuel starvation problem clogged carburetor jets.(clean the carb)
2. Intake leak carb joint/intake manifold.( start your motor get it to idle best you can spray wd40 around the carb joint if the rpms change you have a leak replace the carb joint or gasket/o-ring as needed.
3. crankshaft main seal magneto side leaking or worn main bearing.
check end play on the magneto side remove the cover plate firmly grab the end of the shaft with up an down motion if you can feel it move replace the main bearings and seals.
These are problem that will cause your motor to run lean and hesitate.
Hope this helps you with your problem
Posted on May 10, 2010
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