Question about 2003 Yamaha YZ 125

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2007 125 yz, has a miss before the power valve kicks in. short flat spot then , have keep the revs high to avoid it!!

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There's no extra valve that kicks in to give the bike extra power. The term "power band" is simply referring to the RPM range of the motor that produces the most torque. Make sure the carb is clean and check the spark plug gap and fire. You need a hot blue,purplish fire not a weak white looking fire. If the plug itself is whitish in color you need to richen up the carb if it's black you'll need to lean it out. You should have a chocolate almond color. I'd bet the bike is getting too much air.

Posted on Aug 24, 2009


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02 yz 250 not reving up

Check the compression. It should have at least 100 psi,..if not,then its time to rebuild the top end..IE piston,rings,bore cylinder. If compression checks out,i would start with the power valve. Two stroke dirtbikes power valves are notorius for gumming up and sticking,causing them to not rev correctly.

Aug 31, 2012 | 2003 Yamaha YZ 250

1 Answer

How to start yamaha yz 400f?

pull the choke out, make sure fuel is on, DO NOT turn the throttle before starting. now you have to make sure the cylinder is at the top of the stroke, give the bike a couple short, easy kicks your not trying to kick it over yet, you are just trying to get the piston to the top of the cylinder, as your givivng it the short easy kicks, you will notice that the kick is getting shorter and harded......until you are at the top of the it is ready to kick over, hold the hot start lever in about half way to release some compressionand give it a hard strong kick, if it doesnt start on that kick, make sure you are at the top of the cylinder again and when you are, give it another strong hard kick all the way to the bottom, when it starts immediatly release the decompression lever or you could do damage to the valves. relaese the choke, you dont want to leave the choke on too long because it is a very rich gas mixture and will eat the oil off the cylinder walls after a while. and DO NOT high rev the bike until it is warm, because you need to make sure that oil has gotten to the top end. it isnt a 2 stroke, ya cant make her screem right away.

Apr 21, 2011 | Yamaha WR 450 F Motorcycles

1 Answer

Stops pulling through 2nd 3rd and 4th just flattens out pulls hard ou the hole though brand new cylinder and to end was installed could it be a problem with the power valve postion? the pwer valve arm is...

engine leak down is crucial on two stroke just as much as cylinder compression is engine compression fix the leak first and check for others - spray soapy water over to spot any leaks and kick over with plug disconnected you will see bubbles appear

Feb 23, 2011 | 2003 Yamaha YZ 125

1 Answer

1980 Yamaha xs 400. First start of the spring. Had it started (will only start with kick starter not electric start) - but couldn't keep rpms high enough so it stalled. Went to kick start again and kick...

Sounds like it either dropped a valve, or broke a Connecting Rod. It is never good to get the RPM's too high on the first start. If you have to get them up high to keep it running, you probably have build up in the carb. Make sure it is in Neutral, and the first thing I would do is check the valves. Lift the valve cover off and see if any of them are missing. If not, unscrew the side cover on the left side of the bike(1 inch round cover using a flat tip screw dirver) and the nut in there that is exposed, try to turn it with a ratchet. If you cannot, pull the spark plug and using a pick up magnet, run it down the hole, swish it around a little, pull it out and see if you picked up anything. Last thing I can think of is drain your oil, and see if any metal comes out there, if not, your going to probably be rebuilding. It's not as expensive as it sounds if you do most of the work yourself and pay close attention to your service manual. If you need one, I can send you a digital copy for $30, or a grease proof binder and CD for $100.

Good luck.

May 14, 2010 | 2004 Yamaha YZ 250 F

1 Answer

What pasision do you need for your power valve on a yz 125 1988

well it depends if u have the pv or not if u dnt then just have it wide open, the low end power will be **** but when u get to about 6 tho revs it will kick in and wheelie time, if you do then chech were the pv is and how much movment you have in the servo it should be almost closed when it isnt running and practicly full open about 6 tho revs, the more you open it up the valve opens wider..blablablabla hope was some help

Dec 10, 2009 | 2004 Yamaha DT 125 R

2 Answers

2000 YZ 125 Breaks up at High RPM. We think its the power valve. any tips would be great

check fuel float level as it might not be able to keep up the flow rate at those revs
or the read valve has become weak

Jul 19, 2009 | 2003 Yamaha YZ 125

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