Question about 2003 Yamaha YZ 125

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

Posted by Dean Finch on


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SOURCE: yz 250 2008 possible 5th gear stripped?

I doubt that any gears are stripped. Believe me you would have known it when it happened at 40mph which is where you would have to be in 5th gear. This is a bent shift fork. The actual gear is fine. The slider gear is not moving far enough to engage with 5th gear. The YZ does tend to have this problem in 5th and 1st. "Dirt rider Magazine " did a story on it. Best to let the shop do the repair as the entire motor gets torn down into about 100 parts.

Please rate this solution. Thanks!

Posted on Apr 08, 2009



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SOURCE: my tzr125 2rk 1991 the bike splutters in every gear

gett a high preformance spark plug as i had the same problem with my bike

Posted on Apr 13, 2010

Mr BrokRench

Mr BrokRench

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SOURCE: i have a 1999 yz250

Hello Rick...Try backing the idle air screw out another half to 3/4 turn. The mid range stutter on these bikes is usually from the interface between the needle and the brass bushing just above the main jet. Also check your reeds, a chipped reed will cause the same problem. Clean all the carbon and gunk out of the expansion chamber. If it's real bad you may have to use a torch. Make sure your air filter is clean.
A 165 main jet will give you better response with a 40:1 mix, specially if the plugs are fouling.
..You can also go up a heat range on your plug... I hope this helps.

Posted on Aug 03, 2011

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Im putting my 05 yz 125 top end back together my question was what is the torque specs on the head and on the jug

G'day. The torque specs for the 8mm head bolts is 18ft/lbs.the jug?(cylinder or barrell) is just tightened down even & firm, as there is no acess for a torque wrench.
OK. other things to note.
Clean the cylinder first in solvent(kero or fuel).Then in warm soapy water in a bucket. Dry-(compressed air is best for this-wear eye protection).once dry lubricate all power valves with oil.
Using a clean white rag-soak the end in your 2 stroke oil & wipe the inside of the cylinder surface untill the rag comes back clean(you will need to do it a couple of times-turn the rag over & do it again).Lube the new piston just before assembly-Also pour a little oil down the main bearing oil holes & over the big end too.
Other things to be sure of are-
Piston on the right way round-arrow to the exhaust.
Rings right way up. Some 2stroke dirtbike rings will only go one way up.Look CLOSELY at the ring ends-on the upper or lower surface there may be an etched dot or "T" or "N" or other marking. the mark goes facing up(on both rings unless single ring piston).
rings positioned with end gaps over the locating pins(the ring grooves have a pin in them to stop the ring turning)
Piston pin clips in correctly.
Powervalve moves freely.
Again-watch when you fit the cylinder-it can be tricky to keep the ring end gaps over the locating pins as you feed the cylinder over the piston.
Hope this all helps
Regards(done this a thousand times)Andrew Porrelli

May 04, 2011 | 2003 Yamaha YZ 250

1 Answer

I have a 2000 YZ 426 it was blowing smoke like crazy so i took apart the top end! what all do i need to be looking for?

check your bore for scores/marks wear also the piston,,if they both look good get some new rings,,also check your valve stem seals as they also cause heavy smoke when worn out,,check if your valves are leaking by pouring fuel in the intake port and exhaust port,one at a time and see if any fuel leaks from the valve faces.

Mar 19, 2011 | 2002 Yamaha YZ 426 F

1 Answer

YZ 125 Keeps burnig piston & Ring on Exhaust side cant find problem on 4th or 5th piston & ring

only reason would be your running too lean. which causes more heat, which causes pre-gnition and pinging. Also if timing is off you create more pressure which in turn causes more heat

Nov 09, 2009 | 2004 Yamaha YZ 125

1 Answer

Sparks from my exhaust ??? Yamaha yz 125

if it still runs ok ,it was probably rust or debri from the muffler,if it dosent run ,or preformance changed after the sparks,internal engine damage would be a likely cause,part of a piston ring or something like that

Oct 05, 2009 | 2003 Yamaha YZ 125

1 Answer

How much is my yz 125 worth?

the retail value in good condition is approx $1,500. meaning it looks good, runs good, good tires, breaks,chain and sprokets. but with the extras you have and the after market up grades, i would start with a little higher price.

May 21, 2009 | 2003 Yamaha YZ 125

1 Answer

Just looking for general advice...on FMF Pipe Install

i changed my pipe on 07 dt125lc and did not rejet, seemed fine until i holed a piston. best to rejet me thinks, about £20 instead of £150 for piston rebore bearings and jets plus the time to re build.

Apr 25, 2009 | 2003 Yamaha YZ 125

2 Answers


excessive piston clearance.really needed bore job with oversized piston,not just honed and rings.measure piston to cylinder clearance,check spcifications and verify

Apr 05, 2009 | 2003 Yamaha YZ 125

1 Answer

While riding my yz 125 it just died and won,t kick up again

  • If a hole in the piston then install new piston and rings. Next, clean the carbon off the head and install a new head gasket.
  • If cylinder wall is scared the piston has seized up. Pull the cylinder off and take it to the dealer. Have them bore the cylinder and return it along with a new oversize piston and rings.
  • While at the parts counter, get a new stock spark plug and a supply of Yamalube Two Stroke Motor Oil. You need to add 4 ounces per gallon when filling up. This will be a 32/1 gas to oil ratio. NEVER ride the bike without at least the needed 32/1 mix.
Please rate the solution as a "FixYa" if able. Thanks!

Mar 23, 2009 | 2003 Yamaha YZ 125

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