Question about Yamaha YZ 125 Motorcycles

1 Answer

Bogs down throttling

Hi, i have a 1991 yamaha yz 125. it starts and runs fine. when u pull off it bogs down when throttled

Posted by Anonymous on

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  • Yamaha Master
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Hi, Anonymous it should be noted that your performance issues are not electrical ie. faulty charging system, battery condition, and connections etc. If your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the websites below. Good luck and have nice a day.
UPDATED 2005 YZ125 bog issue with videos
MototipsTV Replacing Float Cleaning Carb
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Posted on Jul 16, 2016

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Posted on Jan 02, 2017

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SOURCE: 1994 yz 250 bogs down

Have you cleaned the carburator ? It seems the main jet has some kind of obstruction.
Try cleaning the carburator and well a tune up would be fine too after the clean , check the plug/s & air filter too.

Posted on May 10, 2009

ollie reece
  • 1167 Answers

SOURCE: Carburetor issue

make sure the oil level is correct also on carb is a screw fiddle with this mixture screw and get back to me if it made no difference i will send a pic in a while

Posted on Oct 06, 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

dmsr63
  • 2050 Answers

SOURCE: I have a Yamaha yz 125 and it keeps fouling plugs

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.

Posted on Jan 09, 2010

  • 162 Answers

SOURCE: I have a 2001 Yamaha 200 blaster 4 wheeler.

You have to adjust the jets on the carb, theres a high and low jet, Turn them both all the way in ( dont force them) just turn until they stop, now losen each one in 1/4 intervals and try running it,

Posted on Apr 04, 2010

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1 Answer

My 1999 yz 125 runs well at high rpm but won't idle and when I give it full throttle it bogs.


Hi, Anonymous and the usual suspects are:
1. Severely drained or faulty battery.
2. Faulty regulator/rectifier or high output coil.
3. Faulty power valve, solenoid or installation.
4. Clogged air filter or exhaust.
5. Cracked or incorrect float level.
6. Float needle is not seating.
7. Faulty reed valve.
For more information about your question and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
UPDATED 2005 YZ125 bog issue with videos
Dirt Rider Magazine
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Jan 09, 2014 | 2003 Yamaha YZ 125

1 Answer

My 1999 yz 125 runs well at high rpm but won't idle and when I give it full throttle it bogs.


Hi, Anonymous and the usual suspects are:
1. Severely drained or faulty battery.
2. Faulty regulator/rectifier or high output coil.
3. Faulty power valve, solenoid or installation.
4. Clogged air filter or exhaust.
5. Cracked or incorrect float level.
6. Float needle is not seating.
7. Faulty reed valve.
For more information about your question and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals
OEM parts for Yamaha
YAMAHA YZ125 Owner Service Manual
Dirt Rider Magazine
UPDATED 2005 YZ125 bog issue with videos

Jan 09, 2014 | 2003 Yamaha YZ 125

1 Answer

2001 yz `125 bogs on hard throttle and blows a lot of smoke


Hi, Anonymous and the usual suspects are:
1. Oil tank/pan overfilled.
2. Restricted oil return line to oil tank/pan.
3. Restricted breather operation.
4. Restricted oil filter.
5. Piston rings badly worn or broken.
6. Valve guides worn and or seals worn, crushed, missing, or have come of guide and are literally pumping oil through the valve guide.
7. O-ring damaged or missing from oil pump at crankcase junction (also results in poor engine performance). 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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YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Aug 25, 2013 | 2004 Yamaha YZ 125

1 Answer

Why is my2001 yz 125 smoke and bog on hard throttle


Hi Glen, you could have a piston cylinder issue do a compression test, faulty carburetor jets clogged or loose air passages or bowl vent block, contamination in the float bowl, a proper rebuild might be in order, or a fuel delivery issue, faulty petcock or fuel tank not venting and for more information about your question please visit the website below. Good luck and have a nice day.
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Aug 25, 2013 | 2003 Yamaha YZ 125

1 Answer

My 1998 yz 125 keeps bogging out about half thottle. We have adjusted the carburetor many times but nothing is working. How do I fix the problem??


Hi, Anonymous it should be noted that your performance issues are not electrical ie. faulty charging system, battery condition, and connections etc. If your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the websites below. Good luck and have nice a day.
HELP YZ 125 bogging out
YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Feb 17, 2013 | Yamaha YZ 125 Motorcycles

1 Answer

I have a 04 yz 125 runs great slight flat spot on bottom end plug is med brown any idears


Hi, Anonymous it should be noted that your performance issues are not electrical ie. faulty charging system, battery condition, and connections etc. If your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the websites below. Good luck and have nice a day.
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YAMAHA YZ125 Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Dec 20, 2012 | 2003 Yamaha YZ 125

1 Answer

Yz250f bogs out at full throttle


Hi, Anonymous and the usual suspects are:
1. Throttle cables misaligned or misrouted.
2. Damaged or restricted fuel tank venting system.
3. Intake system air leak.
4. Vacuum piston malfunction.
5. Accelerator pump leaking or no output.
6. Plugged bowl vent or overflow.
7. Fuel level in bowl too low.
8. Restricted fuel supply passages.
9. Plugged jets or passages.
10. Worn or damaged needle or needle jet.
11. The enrichner valve not seated or leaking.
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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YAMAHA YZ250 LC Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Aug 12, 2012 | 2003 Yamaha YZ 250

1 Answer

2003 yz 250 starts and idles but runs rich and bogs as soon as the throttle is applied


Hi, Anonymous and the usual suspects are:
1. Throttle cables misaligned or misrouted.
2. Damaged or restricted fuel tank venting system.
3. Intake system air leak.
4. Vacuum piston malfunction.
5. Accelerator pump leaking or no output.
6. Plugged bowl vent or overflow.
7. Fuel level in bowl too low.
8. Restricted fuel supply passages.
9. Plugged jets or passages.
10. Worn or damaged needle or needle jet.
11. The enrichner valve not seated or leaking.
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.
2002 yz250 idles fine but bogs and tries to die when twisting the throttle...
Bike dies when you give it throttle
YAMAHA YZ250 LC Owner Service Manual
OEM parts for Yamaha
http://mybikemanuals.com/yamaha/yamaha-yz-owners-manuals

Mar 19, 2012 | 2003 Yamaha YZ 250

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

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