Question about 2004 Yamaha YZ 125

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I'm 5400 ft and running a 490 main jet. the plug

I'm at 5400 ft and running a 490 main jet on a stock motor. the plug is showing lean. Oem spec for sea level is a 410. plug looks the same with a 380 main or a 490 main. why can't i make my bike run rich? New piston,and rings. checked for leaks ( intake and exhaust) . it runs well, just not well enough. any thoughts?

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Try a cooler range plug with the same jets and see w

Posted on Jun 02, 2009

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1 Answer

Would it be possible to keep stock jets as spark plugs showing black not normal light brown.Stock #112-#117-#122tried all showing black plugs.Still bogs at 1500 rpm.


Hi Mick:
Don't know anything about your bike except that it is running rich.
If you can't lean it out manually you'll need to consider smaller jets as one way to change the mixture.

Feb 02, 2016 | Motorcycles

1 Answer

Yz450f running too lean


Hi, Anonymous 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 carburetor 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.
Too lean rich 2006 yfz 450
How To 4 Stroke MX Fuel Screw Adjustment YZF CRF KXF RMZ FCR Part 1 of 2
YAMAHA YZ450F Owner Service Manual
OEM parts for Yamaha
http://www.yamaha-motor.com/assets/service/manuals/2004/lit-11626-17-11_784.pdf

Aug 19, 2013 | Yamaha YZ 450 F Motorcycles

1 Answer

While riding when you twist the throttle the motor hesitates a little


Hi, Anonymous 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 carburetor 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. Here is how and where you compensate trouble:
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, please click on the websites below. Good luck and have nice a day.
http://www.vstar1100.com/1100jetting.pdf
Symptoms of Lean or Rich carb settings on motorcycle
http://www.sloneservices.com/SilverBack/Other-Stuff/V-StarShopManual99-07.pdf
OEM parts for Yamaha
http://www.starmotorcycles.com/assets/service/manuals/2000/LIT-11626-13-36_96.pdf

Mar 21, 2013 | 2003 Yamaha V Star 1100 Classic

1 Answer

Just bought a 2001 WR 426. Has an FMF pipe, no air box lid. Main is a #165 and pilot is a #42.these are stock jets according to shop manual. My elevation is 2500-3000 Ft. Any ideas on jetting?


Hard to give accurate info with out seeing the bike with jetting but I would suggest take a reading from the fuel air screw if the bike running better with the fuel air screw in carbi at 2.5 turns out or more then definitely increase pilot jet up 1 or 2 sizes if you get the bike to run well between one - two turns out on the fuel air screw that is where your jetting should be
I wouldn't be concerned with main jet at all - it should be fine for wide open throttle unless you feeling power loss when you open it right up
also if you are getting backfire or popping when de accelleration that also hints toward lean pilot so a size or two change in pilot jet would be worth trying

Jan 20, 2011 | 2001 Yamaha WR 426 F

1 Answer

What is the best jetting for my 2003 cr 125 with pro circuit pipe,evry thing else is stock,i live in ohio


Hi, Dbengal9 if you have changed your fuel delivery system, air filter size or flow rate, mufflers or exhaust system or a significant change in altitude your carburetors need re-tuning and 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 carburetor 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, the 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 blue links below. Good luck and have a wonderful day.
https://www.procircuit.com/jetting-specs.htm
Carburator Theory and Tuning
Honda CR 125R 2002 Sevice Manual
http://www.partsfish.com/page/oem-parts-for-honda
http://owners.honda.com/assets/OWNERLINK/model/own_man/powersports/2007/2007_CR125r.pdf

May 22, 2010 | 2003 Honda CR 125 R

1 Answer

Why does my kx250f pipe get red hot to where it melts and the exhaust starts too pop so why does it do that?


Several things are possible. The baffles inside the muffler may have partially collasped causing a restriction in the exhaust. The fuel / air mixture may be too lean. A lean mix burns hot. The stock main jet is a #178 (stamped on the jet). Try a richer jet, #180 or #182. Also, use only premium gas without ethanol. Be sure your gearbox oil is clean 10 w 40 motor oil. NO SYNTHETIC LUBRICANTS. Check the radiator coolant flow and temperature to be certain the engine is getting cooled as it runs. Be sure mud /trash is not blocking the radiator fins. Also check the spark plug. The stock plug is an NGK CR8EB. Replace it with a colder plug, NGK CR9EB

Aug 02, 2009 | 2004 kawasaki KX 250 F

1 Answer

Whats the adjustments on a 1996 kawasaki vulcan 800 carburetor. the bike seems to blacken the plugs and run sluggish. it was rejetted however im not sure if the carb was adjusted for the new jets. im...


oem specs run lean if you rejetted and plugs are blacken running rich try air screw first alittle at a time (replace plugs) keep rechecking plugs as you go same diff. if you adjust fuel screw

Jul 13, 2009 | 1996 kawasaki VN 800 A Vulcan

5 Answers

I have a 2005 kx 250 2 stroke and it keeps eating plugs


NGK brand spark plug BR8ECMVX is the stock plug for the bike. The proper gas / oil mix is 32 to 1. That means 4 ounces of 2 stroke oil per gallon of gas. The posting was not clear as to just what the problem is. If you are burning up plugs there may be a air leak in the intake system making the bike run lean. A lean fuel mix runs hot.

Jun 24, 2009 | 2005 kawasaki KX 250

1 Answer

1999 VN800A runs rough and backfires at high RPM.


if it lives above 4000 ft then it will need re-jetting.
Is it stock or does it have a dynojet kit? If dynojet then you need the DJ130 main jet.

Jun 16, 2009 | 1999 kawasaki VN 800 A Vulcan

1 Answer

Acceleration problem


If you are not running an open or free flowing exhaust go back to the stock size jets but use the DynoJet parts instead of the stock.
DJ jets tend to run bigger than oem jets

Jan 28, 2009 | 2005 Harley Davidson XL 1200 C Sportster...

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