Need Help! YZ125 jerking back and forth and stuttering mid second gear!

VloggyBoy
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VloggyBoy
Edited Date/Time 10/30/2020 1:22pm
I just fully rebuilt my 2001 yz125 and when I started it up and rode it, it had a slight bog through mid gear 2nd-4th . Today I did some tinkering with the carb trying to fix the bogging got and started riding . It shifts fine 1st to 2nd but half way through second when I throttle it starts to jerk violently back and fourth and starts to loose power . If I stay on the throttle it will power through and keep riding . PLEASE HELP!!!
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Camp332
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Camp332 10/30/2020 7:13am
10/30/2020 7:13am
Hate when that happens Bro.
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WFO72
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WFO72 10/30/2020 7:37am
10/30/2020 7:37am
I had the same feeling but in 5th gear on my 2002 YZ250 and it was the gear cogs on 5th gear worn. The shift fork kept it from actually jumping out of gear into a false neutral. Replaced a couple gears and shift fork and bingo, works flawlessly now.
Justin_P
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Justin_P 10/30/2020 7:47am
10/30/2020 7:47am
You probably know this if you've gone through the trouble of rebuilding the bike, but you should jet rich to break that thing in (in my opinion). This is tenfold this time of year if you live somewhere that gets cold. I learned this the hard way as a teenager with an rm 125. I did a top end, went to break it in early in the spring, and left the jetting the same as the summer before. It was about 50 degrees out, bike would bog and feel flat, tried to power through it and melted that brandy new piston because it was lean. Before those (or that) ring wear(s) i like to run a generously rich jet and then work my way back down once it is properly broken in. I'm not overly familiar with yz's and not sure if this is your problem, but it's worth considering. -Justin
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Skerby
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Skerby 10/30/2020 8:28am
10/30/2020 8:28am
Have you guys ever got Yamabond on the shift fork rods before? Happened to me, could not for the life of me figure out what was up until I realized one of the shift forks was binding up.
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FGR01
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FGR01 10/30/2020 9:42am
10/30/2020 9:42am
Description is kinda vague, but I think we're dealing with an engine issue here.. not a transmission issue.

That being said, I saw pretty much these exact same symptoms when my buddy put his piston in backwards in his YZ125. Bottom line, the fact that it started after rebuild points to something you did wrong in the rebuild.
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bvm111
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bvm111 10/30/2020 12:51pm
10/30/2020 12:51pm
jerky stuttering usually points to a lean condition and mid throttle is usually the needle. if it ran well prior to rebuild you should be in the ballpark. I would look for something simple first, double check that the clip is in the correct position on the needle, it may have not been fully seated and popped out... it’s happened to me i’m embarrassed to say.
VloggyBoy
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VloggyBoy 10/30/2020 1:22pm
10/30/2020 1:22pm
Justin_P wrote:
You probably know this if you've gone through the trouble of rebuilding the bike, but you should jet rich to break that thing in (in my...
You probably know this if you've gone through the trouble of rebuilding the bike, but you should jet rich to break that thing in (in my opinion). This is tenfold this time of year if you live somewhere that gets cold. I learned this the hard way as a teenager with an rm 125. I did a top end, went to break it in early in the spring, and left the jetting the same as the summer before. It was about 50 degrees out, bike would bog and feel flat, tried to power through it and melted that brandy new piston because it was lean. Before those (or that) ring wear(s) i like to run a generously rich jet and then work my way back down once it is properly broken in. I'm not overly familiar with yz's and not sure if this is your problem, but it's worth considering. -Justin
1
BAD10
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BAD10 10/30/2020 2:56pm
10/30/2020 2:56pm
Switch to 30 weight muffler bearings. If that doesn't work check the flux capacitor.
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huutnanny
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huutnanny 10/30/2020 3:07pm
10/30/2020 3:07pm
Maybe check your power valves. Make sure they aren't getting hung up on something.

Also the float level in your carb. Also that the float valve is working.

Also that none of your jets are clogged.

Also that your needle clip is in the position you think it is in.

Set your air screw to the stock setting.
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