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Discussion Starter #1
Disclaimer: This will be a long post

So this winter I picked up a "basket case" 1988 KX125. It was completely disassembled by the PO and then he lost confidence and sold it for next to nothing. I was in the mood for a project so I decided to pick it up, especially because it came with some new engine parts. Plus I love 80's MX bikes.

Here are the details off the top of my head:

1) Fresh lower end (bearings and seals included in sale)
2) New Crank (included in sale)
3) New Rings (included in sale)
4) New wristpin, bearings, and circlips
5) Piston and cylinder within spec according to my manual and yes it is installed in the correct direction, lol
6) New top end gaskets
7) New Air Filter
8 ) New clutch (fibers, steels, springs, and cable)
9) Carb thoroughly cleaned. PWK 39: 52 Pilot (48 is stock and it had a 68 in it!), 155 main, needle in middle position, air screw 1-3/4 turns out.
10) Stator timing on stock middle mark.
11) New B9EG Plug with new coil wire and cap.
12) KIPS disassembled and cleaned. Re-installed according to manual.
13) 32:1 Maxima SuperM pre-mix

So the bike starts first kick every time. Sounds great at idle, when you crack the throttle it seems to have a slight miss but overall sounds pretty good. Click it into gear and try to pull out and that's when the problem starts. The bike bogs and doesn't even have the power to pull out on its own, I have to push off and then when I give it gas it just bogs and either stalls or I have to grab the clutch and then it sits and idles clean, until I try to ride off again anyway.

32 degrees outside, engine slightly warmed up, WOT, kill switch on, compression 3 test average is 135psi. Not ideal I know (150-190 is) but for a 22 year old 125cc MX bike it is not "blown up" or un-ridablely low. I have owned and seen bikes with much lower run much better than this one, LOL.

The coolant and tranny fluid levels are unchanged so I am saying it is not burning either of those.

I used the old reeds because they looked ok, no chips or cracks, and they are tight to the block. Would worn reeds cause this drastic of an effect?

I do notice a fuel smell, especially when I was performing the compression tests.

So I am looking for ideas. What am I missing? Weak spark under load maybe? Really messed up carb?
 

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Discussion Starter #3
Hmmm I honestly admit to not even thinking about the clutch. The clutch seems to engage/disengage because when you put it in gear the bike doesn't creep or jump. When you let the lever out it seems to have a solid grab and if it was slipping the engine did NOT rev higher. I'll have to look into the clutch adjustment more tomorrow because at this point anything is possible and I am willing to double check anything. The clutch lever, clutch cable, clutch plates, clutch springs, thrust washer and washer on the pushrod are all new because I wanted to start from a clean slate knowing 125's can be hard on the clutch. The only part I really re-used in the clutch was the basket parts.
 

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When a clutch wears and/or is poorly adjusted the bike will take off but will not accelerate as the RPMs of the motor rev to the moon. Basically the power is there but not being output to the transmission/rear wheel.
 

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Discussion Starter #5
When a clutch wears and/or is poorly adjusted the bike will take off but will not accelerate as the RPMs of the motor rev to the moon. Basically the power is there but not being output to the transmission/rear wheel.
I think maybe you misread/misunderstood my first post. As I said the bike is bogging, not revving high. If it was revving I would have looked right to the clutch even though everything is new in the clutch. This bike does not take off, it wants to bog and stall out when you let out the clutch.

Thanks for the responses though. Nobody else has been able to offer any advice, LOL.
 

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Discussion Starter #6
Mystery solved, the pipe was clogged. I originally checked the silencer and looked into each end of the pipe. Today I took a piece of wire and tried to slide it through the pipe (the silencer is clear) and hit a blockage. It was all inside where the light didn't reach. An hour later, use of a wire coat hanger, my air compressor, a huge mouses nest, and one dead mouse later the pipe was cleared and the bike is running great! Much better than I expected a 22 year old 125 to run.
 

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haha nice. you got to watch little animals like that and theyre nests. my friend shredded the belt drive on his polaris trailblazer because a bird made a nest in his air system, :-D
 
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