Question about Yamaha YZ 125 Motorcycles

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Yz 125 fouls spark plug when it bogs. - YZ 125 Yamaha Motorcycles

Posted by Anonymous on

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  • Yamaha Master
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Hi, Anonymous and the usual suspects are:
1. Fuel mixture too rich or enrichner left out too long.
2. Incorrect spark plugs for your kind of service.
3. Piston rings badly worn or broken.
4. Valve guides are badly worn and/or seals worn, crushed or have come off valve guide and pump oil through it.
5. Spark plug cable weak or ignition coil faulty.
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.
http://www.woodsracer.com/portal/forums/showthread.php?6812-YZ-125-Help!!!-Fouling-plugs!!!
Fouling plugs in my yz 125
Yamaha YZ125N1 Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Posted on Jul 14, 2016

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Posted on Jan 02, 2017

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SOURCE: bike bogged down like plug fouled now wont start

Based on the information given, I think you may have a hole in the top of the piston. It sounds like pre-ignition, ( AKA detonation and engine knock ). Pull the cylinder head and check the piston and cylinder head. Sometimes the top outer edge of the piston disintegrates due to the heat. Replace the piston and rings and remove the carbon from the head. Be sure you run 32/1 mix on gas and oil. That's 4oz two stroke oil per gallon of gas. Only use premium gas.

Remove and clean the carb. Be sure the carb mount bolts and carb manifold bolts are tight. An air leak will cause the engine to run hot.

Please rate this solution. Thanks

Posted on Apr 07, 2009

  • 44 Answers

SOURCE: what spark plug for yz 125?

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

wayneman01
  • 301 Answers

SOURCE: my yamaha yz 125 is dumping to much fuel and

There are only two adjustments to make on your carburetor; the idle speed, and the idle mixture adjustment. If the spark plug fouls frequently, first make sure you are using the correct spark plug. Your 1997 YZ125 uses an NGKB9EGV. Then be sure you are using the recommended two stroke oil, mixed to the proper ratio, in the fuel. Also make sure the air filter is not excessively soiled.
With all of the above confirmed and corrected, start the bike and run until the engine is up to normal temperature. Adjust the idle mixture screw to attain the fastest idle and best throttle response. Then adjust the idle speed.
If you are still fouling the spark plug, verify that the carburetor has the correct size jets by consulting your owner's manual. Keep in mind that if you are operating your bike at an altitude higher than about 6,000 feet above sea level, the stock jetting may be too rich. Down-size the main jet in small increments until satisfactory operation and the correct spark plug color is obtained.

Posted on Nov 02, 2009

  • 3 Answers

SOURCE: 2003 Yamaha 125 yz plug fouls pretty quickly.

Like he said BR8EG runs hotter for yamahas and is bettter because br9eg foul quickly. Use castro in 2 stroke bikes. It runs a little higher because its better

Posted on Nov 17, 2009

  • 1584 Answers

SOURCE: yz 125 bog

Sounds too lean to me or lacking fuel.

Partially blocked jet in carb. May have to remove / clean.

Check also that carb butterfly / piston is travelling to full open position.

Posted on Dec 21, 2009

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1 Answer

Bike stutters


Hi, Billy and the usual suspects are:
1. Spark plugs in bad condition or partially fouled.
2. Spark plug cables in bad condition or leaking.
3. Spark plug gap too close or too wide.
4. Faulty ignition coil, module and or sensor.
5. Battery nearly discharged.
6. 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.
7. Intermittent short circuit due to damaged wire insulation.
8. Water or dirt in the fuel system, carburetor or filter.
9. Fuel tank vent system plugged or carburetor vent line closed off.
10. Carburetor controls misadjusted.
11. Damaged carburetor or intake seals.
12. Loose or dirty ignition module connector at crankcase.
13. Faulty MAP, CKP, O2, and or CMP sensors.
14. Incorrect valve timing.
15. Weak or broken valve springs.
16. Damage intake or exhaust valve.
For more information about your issue and valuable "FREE" downloads that you will need please visit the websites below. Good luck and have a nice day.
94 YZ 125 hesitates and bogs at lower RPM
https://yamahaclub.com/forums/topic/31400-sputter-sputter
http://www.motogelnar.cz/manual/YAMAHA/DT125X_RE-05-Service_Manual.pdf
OEM parts for Yamaha
http://www.dt125.cz/download/Owners_Manual-DT125X_RE.pdf

Oct 04, 2013 | 2000 Yamaha DT 125 R

1 Answer

My yz 125 started to bogg down when i put my bike in 3rd gear and i drove it back the next day i went to wash it and i tried to start it. it started but bogged right down till it shut off no matter where...


Ii sounds like your bike cuts out when it get`s hot ? If it does this like clockwork then i guess you have same problem as me with my no limit 125 which does exactly that. i have fixed all connectors & cdi but it still does it. Which leads me to believe some ferrite core in the ignition system is going non-magnetic (called the Currie temp) at this "hot" temperature. It can either be the magnets in the flywheel or the core of ignition coil.I only use this bike for trips less than 10km so i live with it. if anybody can shed more lite plz!

Aug 05, 2013 | 2005 Yamaha yZ 125

1 Answer

MY 1998 YZ 125 KEEPS FOULING PLUG AND THEN BOGS DOWN


Hi, Anonymous and the usual suspects are:
1. Fuel mixture too rich or enrichner left out too long.
2. Incorrect spark plugs for your kind of service.
3. Piston rings badly worn or broken.
4. Valve guides are badly worn and/or seals worn, crushed or have come off valve guide and pump oil through it.
5. Spark plug cable weak or ignition coil faulty.
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.
Why Does My Dirt Bike Keep Fouling Spark Plugs
Fouling plugs in my yz 125
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Mar 18, 2013 | Yamaha YZ 125 Motorcycles

1 Answer

I was ridding my 84 Yamaha yz125 and it was running fine then it quite like it ran out of gas. I took the carb apart blew it out. Checked the fuel lines, it has fuel in the tank (clean). When I went to...


Sounds like it could be as simple as a fouled plug. Change the spark plug and try it again. Lugging a 125 around fouls plugs really easily, you have to open it up and clean it out occasionally.

Jul 24, 2010 | 2003 Yamaha YZ 125

2 Answers

What spark plug should i run in my 2003 YZ 125?


Run a B9ES if you don't have a problem with fouling. If you do have a problem fouling, run a B8ES. Both of these plugs are available at auto parts stores for a few bucks each.

The stock plug was a BR9** - the R indicates a resistor plug which is not needed.

Scott

Jun 18, 2010 | 2003 Yamaha YZ 125

1 Answer

Im losing spark after my yz 125 engine warms up, why?


Hi, Jeffreyo76 and the usual suspects are:
1. Fouled spark plugs.
2. Severely discharged or a damaged battery, should have 12.5 volts or better and be able to pass a load test if necessary.
3. 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.
4. Loose connection at ignition coil or plug between ignition sensor and module.
5. Spark plug cables in bad condition, shorting / leaking, spark plug cable connections loose.
6. Faulty ignition coil or electronic control module or CDI box.
7. Faulty CKP, CMP, or BAS sensor.
8. Faulty ignition switch.
9. Tilt sensor needs a reset.
10. Security alarm failing to disarm needs 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
99 yz 125 no spark Yamaha 2 Stroke
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

May 19, 2010 | 2004 Yamaha YZ 125

1 Answer

I have a Yamaha yz 125 and it keeps fouling plugs and bogging out could it be the top end?


A compression test will tell you your condition. (Throttle wide open while doing that) If that's good, your jetting is too rich, could be the issue.

Jan 09, 2010 | 2004 Yamaha YZ 125

1 Answer

Yz 125 bog


Sounds too lean to me or lacking fuel.

Partially blocked jet in carb. May have to remove / clean.

Check also that carb butterfly / piston is travelling to full open position.

Dec 21, 2009 | 2003 Yamaha YZ 125

1 Answer

Yz 125cc 2003


Black spark plug means too rich , you will have to replace the spark plug since it has foul up and reset the air mixture screw on the carburator 2 and 1/2 turns outwards.
Check the air filter too.
Hope this helps.

May 23, 2009 | 2003 Yamaha YZ 125

1 Answer

My yz wont start, changed spark plug it ran for 1/2hr then died


Couple things- 1. If the plug was dirty after 1/2 hour you have either the wrong heat range plug(too cold) or 2. a fuel/carb issue. Buy a hotter NGK plug, ask for help the numbers don't always make sense. Use only full synthetic 2 stroke (I always liked bel-ray) and fresh 93 octane fuel. When you find a plug that works good buy a case of them, 2 stokes will foul plugs period. And some advice with your solution, never head into the woods without a spare plug, they will foul at the absolute worst time.

Don't forget to rate please!

Mar 13, 2009 | Spark Plugs BR4HS Plug 10/BX #3322

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