1981 YZ125 Jetting Question

dcfitz
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dcfitz
My rebuilt 81 YZ125 is sluggish and seems to miss and bog on the pilot jet. Full throttle it flies! So, do I start with the air mixture screw?
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EastFlorida
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EastFlorida 10/28/2019 4:15am
10/28/2019 4:15am
Did you ever get it figured out?
dcfitz
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dcfitz 10/28/2019 6:56am
10/28/2019 6:56am
Haven’t messed with it since the post, but from the reading I’ve done, I think starting with the air mixture screw would be good. I hope to get it out, soon, so I can ride it to get I warmed up and then do the adjustments.
special K
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special K 10/28/2019 5:35pm
10/28/2019 5:35pm
The 1981’s definitely had a a flat mid range. I have 2 of them. Set the carb to factory settings after a thorough cleaning and if still bad check other things first before blaming carb. Clogged exhaust ( very common with 20:1/32:1 mixes. Broken or weak reed valves, make sure float is set correct as to not fill up to high when not at full throttle. If all that checks out the old solution was to drill the air box cover to get more air. I would not do that as the air box covers are getting real scarce. Just test run it with the cover off and if it helps cut a piece of aluminum mesh to shape and screw it on to keep the big stuff out and more air in. If I’m correct you can get a bog from to much fuel that’s not burning on correct air or not enough air to burn correct fuel. Sounds like the same thing but it’s not. Check your compression and do a pressure test on the crank case. The 2 strokes can be complicated for such a simple engine.
dcfitz
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dcfitz 10/29/2019 7:09am
10/29/2019 7:09am
Thanks for the thorough reply. I drilled out the sides of the air box back in 1981, so that’s a done deal. I rebuilt this carb with new stock jets and set the float level, as well. The day I was riding was cooler than it has been, so maybe it’s running lean in the mid range. I’ll play around with it when I take it out again. Thanks so much for your reply!

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