Question about Yamaha YZ 125 Motorcycles

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How do you know you should go with a bigger main jet? What exactly would it do for my 2001 YZ 125?

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A bigger main jet will make the bike run richer which means more gas.
unless you have changed something on the bike which would involve a bigger main jet like porting or something like that. I wouldn't mess with the jetting.
if you are trying to get the bike tuned properly, there is an adjustment screw on the carb, but I would put it in the hands of a pro.
You can easily blow your bike up messing with jetting.

Posted on Jul 21, 2009


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Bigger jet is not the problem. More fuel would be put in and you said that it runs well at the top end. So it is not a fuel shortage issue.

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Alrite ? Iv got a yz 125 2001 it's had new piston

Hi, Dean for this situation I would call my local dealer or reputable shop's service/parts department and inquire about any possible quick fix, answers, or parts inquiry. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
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What is the size of main jet of YZ125?

  • Main Jet: 410
  • Main Air Jet: 2.5
  • Jet Needle: 6BFY43-74
  • Needle Jet: S-1
  • Pilot Air Jet 1: #40
  • Pilot Outlet: 0.7
  • Pilot Jet: 40

Jun 05, 2011 | 2003 Yamaha YZ 125

1 Answer

Need spects for carburetor main jet on mikuni ucal and spects for pilot air jet 1 and pilot jet 2

Site above has all the parts and specs for your bike. Jet ranges are large for a YZ as many mod's are available and riding conditions contribute largely to a peaky 2 banger. Start with #40 pilot, and #420 main. Trial and error from there. Cheers.

Apr 26, 2010 | 2003 Yamaha YZ 125

1 Answer

My yamaha yz 125 stalls at full trottle. can you tell me why

You might have some dirt or something floating in the carb bowl, and at full throttle it may **** it into the main jet. I would go through the carb thoroughly.

Apr 17, 2010 | 2003 Yamaha YZ 125

1 Answer

Have a yz 125 2001 need help with pilot screw?

125 bottom end power is almost non existent, but u could look on yds possibly for jetting and carb tuning specs, it all depends on altitude and temperature.

Apr 08, 2010 | 2003 Yamaha YZ 125

2 Answers

What jets does a vxr200 take i have a vx 125 and jus bort a malossi 210 and dont no what jets to put in do i keep the same 1s ??

hi,,your carb wont do...its not big enuf airflow..but .the main jet for a vxr200 is a 1.18 or 1.20 (the 125 main jet is a 1.07).
i am haveing the same probs with a vrx 200 i bought..they run fine up 65mph & then seem to run out of fule...but chime back in when drops below 65mph..i have put the bigger main jet in & it doesnt make no diffrance..the carb carnt get enuf air to go above 65mph..carb of a 180-200 will sort it out but it may still need rejeting to suit big bore kit!!....also there is the carb of the dna 180 scooter as well.....good look..Howard

Sep 29, 2009 | 2005 Gilera Runner VX 125

1 Answer

Will main clutch casing fit yz 125 2001 from 1997?

Hey Ryan! Long time since hearing from you.

When you say "main clutch casing" do you mean the right side cover for the gearbox or do you mean the primary driven gear (AKA "clutch basket") that the clutch boss (AKA "clutch hub") and all the clutch plates fit into?

If you mean the right outer casing > they are slightly different, '97 pn 4JY-15431-10-00 and 2001 pn 4JY-15431-12-00. The entire clutch is the same from 1997 through 2001.

Jun 07, 2009 | 2003 Yamaha YZ 125

1 Answer

2003 yahama yz 125 radiator

Google " motorcycle salvage yamaha ". You should be able to find a good used radiator there.

Please rate this solution. Thanks

Apr 09, 2009 | 2003 Yamaha YZ 125

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