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Old 09-16-2019, 02:37 PM
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Default Suzuki RM125 Running/Adjustment Trouble

Hello, I purchased a 01 rm125 back a few months for a rebuild project, as my first dirt bike. It ended up that one of the exhaust valves had broke and was hitting the piston which is why it wasnt running. The cylinder was also*shot, so I got a used one in great condition, bought a new exhaust valve and got a new top end kit. I put it all back together and started right up, but soon after I was having symptoms of an air leak. So i made a leak tester and found part of the crankcase gasket was missing causing a large amount of air to leak. So I ordered a new gasket, took it all apart, and replaced it.*

Now I have the bike all back together again and i cant seem to get it to run right. Part of the problem is im new to dirt bikes and 2 strokes so I dont know what its supposed to sound like, but I know how it sounds right now, is not right. I think i got it to idle right, it might be rich im not sure, but when I try to rev it up its not smooth at all, and kinda sounds like it hits a rev limiter, or its choking,*at one point and wont go much higher than that, and thats only at like 1/4 - 1/2 throttle.*

The main jet is a 450, which I understand only effects the top of the throttle range. The pilot jet is a 25. The needle I believe is stock and I just put it on the middle position.

It seems like its smoking a lot when I try and rev it up, but then again im new to 2 stokes and that level could be normal. If I had to guess it is too rich but im not used to having so many things to adjust and having to adjust off the sound, and I just don't now what to adjust.

Here is a link to a video of it, not sure if it will work or not

Any help would be greatly appreciated, thanks!*
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Old 09-16-2019, 03:40 PM
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Have you tried to adjust the exhaust valves? There is an adjustment for them and it controls how fast they open. I would start there.

Paw Paw
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Old 09-17-2019, 09:25 AM
cowboyona426's Avatar
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In addition to what PawPaw said, I would go over all the basics.

Do you have good fresh gas mixed at the correct ratio?
Is the air filter clean?
Are any of the carb vent hoses pinched or blocked?

Also, did you happen to check the condition of the reeds when you had it apart?
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Old 10-01-2019, 12:00 AM
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"main jet is a 450, which I understand only effects the top of the throttle range"

thats a common misunderstanding. The main jet also affects idle running at closed throttle.
see 2 Stroke Carburetor Tuning
Besides the jetting you need to check for crank seal leaks and frayed reeds.
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Old 10-01-2019, 01:37 AM
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Posts: 922

Read the plug.
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