Question about 2004 Yamaha YZ 125

1 Answer

Just did new top end on a 1989 yz 125 it has fire compression and wont start before i did the work i could pull start the bike but would not idle or when you gave it a little throttle it would die

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  • Yamaha Master
  • 39,932 Answers

Hi, Lissahere and the usual suspects are:
1. Fuel tank empty.
2. Fuel supply valve/petcock turned off.
3. Fouled spark plugs.
4. Engine flooded as a result of overuse of the enricher.
5. Vacuum hose to the fuel supply valve/petcock disconnected, broken, cracked, or pinched.
6. Fuel valve/petcock or filter clogged.
7. Fuel line to carburetor or throttle body pinched or kinked.
8. Carburetor float stuck.
9. Fuel injectors clogged.
10. Severely discharged or damaged battery, you need 12.5 volts or better and be able to pass a load test if necessary.
11. Check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
12. Loose or corroded wire connection at the coil, battery or plug between ignition sensor and module.
Spark plug cables in bad condition and shorting, cable connections loose, or connected to the wrong cylinders.
13. Ignition timing incorrect due to a faulty ignition coil, ignition module or sensors (MAP, CMP, CKP, O2, TPS, ETP, IAC,or BAS).
14. Faulty neutral, clutch lever, or kickstand safety switch.
15. Faulty fuel pump or fuse or relay.
16. Faulty CDI box if applicable.
17. Tilt sensor needs a reset.
18. Security system not disarming alarm needs a reset.
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.
Dirt Rider Magazine
yz 125 wont start
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Posted on Jul 19, 2016

6 Suggested Answers

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  • 2 Answers

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Posted on Jan 02, 2017

FoRdMaStEr
  • 51 Answers

SOURCE: 1997 yz 125 wont start, please help

2 stroke bike are very dependent on compression. and being a bike that is 12 years old my best educated guess is that the top end needs to be rebuilt. i usually have to have the top end done on my honda about every three years.

Posted on Jan 13, 2009

  • 3567 Answers

SOURCE: 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!

Posted on Mar 23, 2009

  • 3567 Answers

SOURCE: i have a keeway 125 bike new idle prob

Pull the carb off the bike and clean it inside and out. Be sure main jet is clear. Remove the two screws on the outside throat of the carb and spray into the screw holes as well. Be sure to put these two screws back in the same hole they came out of. IMPORTANT > > > do not tighten these two screws down. Only screw these in until they LIGHTLY seat. Now turn each screw one and one half turns outward.

Put the rest of the carb back together and install the carb. Turn the gas on to let the float bowl fill then start the engine. Chances are this will fix the problem. I suggest that you install an in-line fuel filter to prevent this happening again.

Last item> You should have just a little bit of slack in the throttle cable where it goes into the top of the carb. Not more than 1/16". Let me know how things turn out.

Please rate this solution as " FixYa " if all goes well. Thanks

Posted on Mar 28, 2009

  • 3567 Answers

SOURCE: I have a 95 yz 125 head and 98 yz 125 bottom end.

You have a 50/50 chance that they will work okay. All the mounting holes need to line up and the cooling holes as well. Get a head gasket for the '98 and see if all lines up. Will the exhaust pipe fit the '95?

Posted on Apr 30, 2009

  • 200 Answers

SOURCE: crack in my yz 125 2001 crank case

You know aluminum can be welded very successfully now, so best bet is to remove that case and take it in to a good welder..You can ry the quick fix (JB Weld) is what i recommend, but success is rare !....good luck to you my friend...Tim

Posted on May 10, 2009

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I have a 2000 yz 125. Melted a hole in the piston but didnt score cylinder. Replaced top end. Wont start. Has good fire. Crank case oil was a little grey. New plug,fluids,fuel.


I would be checking compression it may not be visible score on cylinder but it does not take much to loose compression on small bore motor with one piston ring and 11 years old

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Jun 03, 2010 | 2003 Yamaha YZ 125

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Yz 125 2001 model. i went down to the garage and kickstarted the bike she fired up no problem then the engine cut out after a minute now the kickstart is real heavy too push down and will not start, any...


Sounds like the piston seized.
Pull the spark plug and hand crank the engine if the piston moves up and down with little effort your ok but if you have a lot of resistance top end rebuild needed.

May 26, 2010 | 2003 Yamaha YZ 125

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Change plug then use a small amount of starting fluid then kick it if it fires then dies your carb needs to be cleaned pull float bowl pull both small brass jet screws and clean they must be clear to see through when put up to a light reassemble and you should be good

Jan 31, 2010 | 2004 Yamaha YZ 125

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Apr 07, 2009 | 2001 Yamaha V Star 1100 Classic

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

5 Answers

1997 yz 125 wont start, please help


2 stroke bike are very dependent on compression. and being a bike that is 12 years old my best educated guess is that the top end needs to be rebuilt. i usually have to have the top end done on my honda about every three years.

Jan 12, 2009 | 2003 Yamaha YZ 125

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