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Problem with my YZ125 bogging

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Took my 01 YZ125 out for the first time this season. When I put it away in the fall, it was running great; no problems whatsoever. I changed all the fluids, new plug, new air filter, etc. yesterday and mixed up a fresh batch of 93 octane fuel with Yamalube 2R at 32:1 (same mix that I always use). Started the bike in my yard and let it idle, no problems. Rode around the street in 1st and 2nd gear, no problems. Loaded the bike on the truck and headed out to the sandpit where I ride.

 

When I got there, I let the bike warm up for about 10 minutes before riding. Pipe was hot to the touch and it was revving perfectly. My friend that was with me mentioned how the jetting seemed to be spot on. Normal amount of smoke coming out of the exhaust during idle and rev. Got on and it was absolutely ripping for about 2 minutes until it let out a loud backfire and died. Was very smoky (according to my friend) and smelled like burning oil. Lots of oil running out of my silencer and if you put your finger inside, it came out covered in oil. If I tried to start the bike again, it would idle for about 5 seconds before dieing. I have a clear fuel line and we noticed that no fuel was being sucked in so we took the carb off, drained the bowl, and put it back on. That seemed to fix the problem.

 

Bike will now idle as it should but when I twist the throttle, it bogs down real hard. Tried a new plug and that didn't help. I got on and rode around in first gear and it was extremely jerky and could only go about 5mph. Before going crazy tomorrow and tearing everything apart, I am hoping to get some ideas as to what this might be.

 

Other things to mention:

- Bike has the JD jetting kit and is set up as per J.D.'s recommendations. Carb not been touched since last year.

- Stator has not been touched since last year.

- V-Force reeds - came in the bike when I bought it 2 years ago. Thinking they might have chipped and need to be replaced.

- Powervalves - been having an issue where one of the powervalve pins/ dowels comes loose, rendering the one of the 2 powervalves useless (either stuck in the open position or closed position). I have had it welded a couple of times already and I'm thinking maybe it came undone again. I have had it stuck open before and never noticed any change in performance. Never experienced it stuck closed but have heard this could cause a bog.

- Piston and ring have approximately 12 hours on them.

- Fatty pipe - thinking that there may be a pool oil sitting in the low spot of the pipe, restricting the exhaust flow.  Could blow compressed air in to see if anything comes out.

 

 

 

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I would also make sure that your carb air screw is set properly. I rebuilt a 2007 yz125 and same thing, bogg at lower rpm's when I pulled on the throttle. I screwed in the air screw to lean out the mixure and it runs like a champ now.

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i bought an 03 yz125 that sat for the winter, and it wouldnt rev beyond idle. I bought a full carb rebuild kit for 20$ and the needle valve and seat was worn out. Never ran better after that

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Took the bike apart today..

 

A few things to note:

 

It appeared that the orange wire coming from the CDI box was not fully plugged onto the ignition coil. Not sure if that came off when I removed the tank or was like that yesterday and is part of the problem.

 

Reeds look fine.

 

The right power-valve that I previously had welded, was broken again. The little rod/dowel moves around and the spring no longer is able to move it back and forth like it should. I believe the valve was stuck in the closed position. The whole assembly was also full of oil. Going to try to find a new PV on ebay and will put everything back together as well as a new piston and ring.

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