Question about 2003 Yamaha YZ 125

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I was wondering what kind of jets and needles I should put in my 99 yamaha banshee after I just rebuilt it. It is bored 80 over, has fmf pipes. what would be a good jet to start with?

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Whatever a professional manual or pro sez-jets are a delicate thing cause you cud end up rebuildin again--the web n fixya has books or getta hold of a motocrosser

Posted on Aug 26, 2010


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1 Answer

I put a fmf slip on, on my 06 Suzuki 125 drz-l and it is running a bit lean I was wondering what size I should go with on the jetting?

I take a small drill and go up to the nearest 0.1 say if you have jet with 104 bore, go to 1.1 drill, means 110 bore, next is 1.2 and so on,
When you find the right size, then buy a jet in that size.

Sep 11, 2014 | 2006 Suzuki DRZ 125

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Wont stay running/just rebuilt,,67mm all new

Hi there . These brothers know what to do. Trust me i feel your pain.


Oct 30, 2017 | Yamaha IR Blaster

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Need 3000 ft elevation jetting for 2002 yz250 with fmf SST pipe and fmf spark arrestor

Hey Anon,
Proper and correct jetting is something that can only be achieved in person by a REAL MECHANIC that KNOWS how to "read" a spark plug,,,With the mods you mentioned.. you need to know the stock jet sizes..a close guess would be reduce the main jet by two or three steps and lower the needle one clip position... oil mix should be at least 32:1....or better yet 28:1.. KEEP the oil mixture and jet the carb for performance....( I see TOO MANY IDIOTS that instead of jetting a carb correctly just reduce the oil ..some as low as 50:1(INSANE) just to keep from fouling plugs.).. then WONDER why their engine doesn't last long... hahaha????

Aug 25, 2013 | 2005 Yamaha yZ 250 F

1 Answer

Hey guys, I have a 03 banshee that a just had completely rebuilt. Crank, pistons, pipes, the works. When I got it back it ran great. Then we noticed it seemed to not be getting enough fuel in the power...

1. How could you tell it wasn't getting enough fuel in the "power band?"..i.e. the upper rpm range...?
A "power band" is simply the RPM range where the engine makes the most power.. it is more pronounced on modified two-cycle engines.. it is NOT something you can buy or have "installed".
Adjusting the float level only accomplishes getting more (or less) fuel in the carb bowls to make it available to the jets. >>The JETS are what (and ONLY what) gets the fuel to the engine!<<
Spark plugs are read to tell whether their is a need for a jetting change.. if you do not know how to do this - STOP tinkering with your engine-PERIOD!
You need a factory shop manual to get the necessary specifications of the ignition system,,(resistance values)...then and only then can you adequately check the wiring and related components...
What is a hot rod crank? I have built numerous banshee racing engines.. just wondering about yours.. $3000 in an engine.. it should have come with 34mm carbs, new head, ported cylinders, etc...jetted by the person that built the engine... if it didn't you need a new engine builder!!!
Do you live near North Alabama??

Mar 06, 2017 | Yamaha 2004 Banshee Base

1 Answer

I have a 06 banshee with fmf pipes it won't start

sounds like your rings are shot, Prob only runs at high rpm & dies when gets lower and wont tick over, try kicking it over slowly with your foot can you feel the compreesion cycles , if not defo rings

May 27, 2011 | 1986 Yamaha RD 350

1 Answer

I have a 98 yz125, i race it but seem to have a lack in power in certain areas, ive changed my jetting a few times but seem to find the power else where and NOT where i need it, as of rite now im running a...

I would first make sure the power valve is decarboned and moves smoothly. Jetting is trial and error as so many things can affect the mix. Temp. humidity, gas quality, oil ratio etc. Tht being said you can make small changes and keeping a log with results. First write down baseline settings. Include main jet and pilot jet numbers found stamped on the jets and needle number. You don't say where it is you are trying to get power. 125s have poor bottom mid power, it is all on top for racing. Don't change and race or you may keep going when you should stop and melt something. Try to test at the altitude where you will race and read the plug often, cleaning or changing the plug between tests. Be alert for the surging feel of lean mix with racing idle do not let this continue. Remember 0 to 1/4 throttle, pilot and needle base width. 1/4 to 1/2 throttle controlled by needle mid taper. 1/2 to 3/4 throttle needle tip and main. 3/4 to full is the main jet. Find out the stock settings and make sure to start near there. I don't know about a spes pipe but pro circuit has charts for jetting and maybe a support line. I really feel you will get more from a clean powervalve, repack the silencer, clean airfilter and maybe v-force reed. Gearing can offer some options. I just read about a James Dean jet kit for cr250 that puts more power in the low mid. I might try that for my bike. Good luck, just remeber " too lean, too long- too bad"

Apr 06, 2011 | Yamaha YZ 125 Motorcycles

1 Answer

Yamaha banshee. Just rebuilt top end and has been bored 80 over. Starts but is bogging down in low rpms. It seems to run ok in high rpms. I cleaned the carbs and replaced the reeds.

Check the plug color to see if it is normal. I would put new spark plug caps and new spark plugs on the machine and see if that helps . From what you describe , if the spark plug caps do not work , you will probably have to either , adjust your air screw setting or change your pilot jets up one size to compensate for the other changes.

Aug 17, 2010 | Yamaha YZ 125 Motorcycles

4 Answers

Banshee wont rev

Usually related to TORS, specifically the safety switch in the clutch/park brake assembly. If it's defective the engine won't rev. Solution: look for a TORS removal kit.

Jun 16, 2009 | 1986 Yamaha RD 350

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