Top 10 2003 Yamaha YZ 125 Questions & Answers

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Question

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how to clean carb on yz125?

I have a 2005 yz125 and the bike runs well in low to mid power but when I open the throttle there is no power. It feels like the gas cuts off and the bike **** down. What do I need to do to clean the carb? Do I just pull it off and spray carb cleaner? Do I need to double check anything else? Thanks in advance for the help...

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Answer

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ALWAYS have a fire extinguisher on hand when working on carburetors.
Remove the water trap bowl at the bottom of the petcock, (gas valve). Is there any water or trash in the bowl? Drain a cup of gas from the tank. Is there any water or trash in the cup? Dump it, clean it and re-mount it, ( not all bikes have a water trap bowl ).

Drain the carburetor. There should be a large plug on the bottom of the carb float bowl. Remove the plug then replace it after the fuel drains. Turn the gas back on and wait a minute for the carb to fill with gas. If the bike doesn't start and run properly then shut off the gas and remove the carburetor from the engine.

Remove the float bowl and clean the entire carb with a spray carb cleaner from the auto parts store. Wear protective goggles to avoid getting spray in your eyes. Spray into all the little airways and fittings in the carb. Remove the idle screw and the air screw on the outside throat of the
carb and spray into the screw holes as well.
< < READ CLOSELY > >
Be sure to put these two screws back in the same hole they came out of. IMPORTANT > do not tighten these two adjusters down. Only screw these in until they LIGHTLY seat. Now turn each adjuster one and one half turns outward. Put the rest of the
carb back together, clean the air filter and install the carb. Let the float bowl fill then start the engine. This process should get you back on the road. Post a comment to get back to me if it doesn't.

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Posted on Jun 16, 2009

Question

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yamaha yz125 wont start...

The other day i was riding my bike, it worked fine. The next week i tried starting it and after well over 100 kicks it still wouldn't start, I have tried a new spark plug but still wont work. What could be the problem?

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you should try cleaning your carb i dont know how often you clean your air filter but if you havn't done that you should do it also.after you do that turn the gas on lean it over till gas runs out the over flow and give it choke no gas and try kicking it over.you should be able to just loosen up the clamps on each side of the carb and twist it so you can get to the float bowl,unscrew the four screws and blow it out with a air nossle you can try that before you go through the troubles of taking it off to clean it.

Posted on Nov 23, 2008

Question

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what spark plug for yz 125?

i have a yz 125 2001 model what spark plug should i put in it and what heat ratiung etc? thanks for any help. Ryan Dundas

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Answer

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I have a dennis kirk book, the correct spark plug is a --BR9ES--(NGK)

i always used SAE 10w-30 oil on all my dirtbikes,
no transmission fluid

for the chain you should move the back tire back until the chain is at a snug tension

Posted on Apr 24, 2009

Question

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Yamaha YZ125 Clutch not disengaging

I have a 2002 Yamaha YZ 125 and the clutch is engaged and wont disengage, it is stuck in third gear so I can't even start it. I was wondering if there was some easy way around it? I have taken off the clutch side of the gears and of course it is freed up, when I put the pressure plate back on it gets engaged again, I just bought it off someone that KINDA knows stuff about these bikes and I have been a mechanic for vehicles for about 3-4 years so I know the basics with these bikes... Please let me know if anyone can help...Thanks, Vinny

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I would be more concerned with the stuck gear than the clutch, but we will start with the clutch.

02ccdb2.gif The push cam may be bent or deformed and the push shaft may be bent. Assuming the ball bearing is in place, the cam and rod are all that can really go wrong. The rod slides out of the left center case. You will need to loosen the springs to get the left side cover back in place. Roll the rod on a flat surface to see if it is bent. I fear a bent shift fork is causing the gearbox to be stuck in third. Fix the clutch and then post a comment to get back to me.

Posted on Jul 26, 2009

Question

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yamaha 125 grizzly starts and idles when choked but dies when acc

our 125 grizzly will start when choked but dies when given gas. My kid ran it out of fuel last year and it did the same thing. The main jet was plugged with gelled gas. This year it acts the same but the main jet was okay. I cleaned up the carb anyway and put it back together. Minor improvement. I have put in a new plug and do not have the air cleaner hooked up right now and it still will not run. I also put on a clear gas filter and can see that there is fuel going to the carb. Any Thoughts?

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Answer

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check that reed valves not sticking and check the pilot jet its prob. half blocked. have to stick a very thin wire through it.

Posted on Aug 12, 2009

Question

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Fuel ratio 2 stroke yahama YZ125

What is the Fuel ratio for a 2001 2 stroke yahama YZ125.

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Answer

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32:1--40:1 Any less than a 32:1 mix and she will smoke and foul plugs(not to mention wasting money on mix) Any more than a 40:1 mix and your top end ect. is not being lubed enough which will lead to costly top end and engine repair..... 40:1 is good for a synthetic mix...And 32:1 for a non synthetic mix.... hope this helps ya....

Posted on Sep 12, 2010

Question

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1999 yz 125 service or owners manual

ive searched for a week now for a free download of the service or owners manual for my 99' yz 125. Its no were to be found so any help would be great

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Answer

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www.denniskirk.com-1-800-969-7504orwww.j&pcycle.com-1-800-318-6847. they should have it.

Posted on Mar 26, 2009

Question

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2000 yz125 - Water pump seal change

My 00 yz125 was dripping coolant from the weep hole so i went out and bought the pump gasket and seal but i am stuck at the impeller wheel - do i need to take the entire casing off to get the impeller wheel off??? tried putting the bike in gear and holding the tire with no success...

Thank you

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The two seals in the diagram below are separated by the casing they fit into. The impeller is threaded to screw onto the impeller shaft. I think you already knew that by your "holding the tire" note. The center casing does not get split. The right casing does remove then a wrench is used on the shaft as the impeller unscrews counter clockwise. It is risky to "Lock the wheel" because the gear on the impeller is very thin and can break.

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Posted on Jul 01, 2009

Question

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power valve position and installation for yz 125

power valve position and installation for yamaha yz125 two stroke , whats the proper position of the opwer valve arm right side of the engine thanks

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The proper adjustment is achieved when the notch in the actuator lines up with the pin hole in the cylinder casting.

Posted on Nov 13, 2009

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how do i set the timeing on a yz400f or 426

how do i set the timeing on a yz400f or 426

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Hi Leewy....Ok...Turn the crankshaft counterclockwise until the " I " mark on the rotor is aligned with the stationary pointer on the crancase cover.Fit the timing chain onto both camshaft sprockets and install the camshafts on the cylinder head.The camshafts should be installed onto the cylinder head so that the exaust cam sprocket punch mark " E " and the intake cam sprocket punch mark " I " align with the surface of the cylinder head,both marks facing out of course towards their prospective ports.thats about it Lee.Please leave some feedback if this has helped in anyway. from tilleydog at Moto Headquarters.

Posted on Jul 17, 2009

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