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rm125 jetting

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hey everyone, was hoping you could help me out with my jetting problem!

my bike is a 1988 rm125

I need to get this bike jetted right! my cabin is up at 3600', temperature most of the time I am riding hangs around anywhere from 50-65 degrees, maybe cooler in the morning. The riding up there is forestry roads, and doubletrack trails, nothing technical but it gets really muddy!! I got to ride it for the first time on the long weekend. heres the scoop:

-runs rich, plug is black, lots of spooge out the pipe.

-has 320 main, and 20 pilot

-pilot circuit seems fine, good throttle response and no bogging, it can idle all day long when its running. I rode it around on muddy slushy trails all weekend, rides great on trails tractoring through mud, or slowly riding around things. this is my first bike, I didnt want something with too much power, and I love how it is in the woods. Throughout the day I was fiddling with the air screw, seems happiest between 1.5-2 turns out, which is good!

The problem is between 1/4-3/4 throttle where you ride most of the time when you are cruising on the roads, it chugs and hesitates. it will go away if you either let go of the throttle or give it more throttle. goes away instantly. LOTS of top end power, scary actually, but in between tractoring and going insanely fast is where the trouble lies. reading up a bit on jets, this would point to the jet needle. I tore into the carb, and discovered that my jet needle was bent, and had lots of plier marks on it from someone trying to bend it back! do you guys think this could be causing my problems?

For starters I was going to replace the needle, and try 1 size smaller main jet but I cant get one from the suzuki dealer. Where can I get a new needle? my bike has a mikuni TM carb, I suspect there are other manufacturers that use the same carb, where can I go to find parts for it?

As for my mid range bogging issue, does that sound right? my needle is bent and scratched up so bad it causes the bike to come on too rich at mid throttle? What can you recommend for jetting for 3600 ft elevation and cool dry weather? Where can I buy jets for this bike? Are jets sort of a universal thing for each manufacturer(like mikuni) or do they change every couple years, will a jet for a new mikuni carb fit into my old mikuni carb sort of thing...

A few more things to add here that might mean something to someone with more experience in this sort of thing: my bike came with no silencer on it, I intend to get one, but can a missing silencer be causing this problem? Also, I will admit another mistake: I used the premium Canadian Tire brand 2 stroke motorcycle oil, it was all I had. Could this be the cause of the problem at all? The suzuki dealer I went to today advised me to change oils and hope that the problem goes away. I bought some Bel-ray synthetic, but I kind of doubt that was the problem, the problem is with the jetting! Sure, my engine wont last as long if I were to continuously use that oil, but cause it to run poorly? I dont think so. I mix at 32:1.

anyways, I hope someone can point me in the right direction! this is my first dirt bike, I am definately hooked on the sport and excited that I was able to turn a pile of scrap metal into something that rides great!

Thanks for the help!

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If the needle is bent I would replace it, you can get the OEM I am sure with no problems. I would check aftermarket sources on the needle like Parts-Unlimited/Tucker-Rocky or call bikbandit.com and check with them.

Check the auction sites for a silencer, you can get one at a good price. I would always use a good quality pre-mix oil and premium fuel.

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Use a good bike two stroke oil. Get a new needle. (same size for now) AND GET A SILENCER!!! There are probably no animals and many very angry people within a few miles of the cabin. And the silencer missing would affect the way it runs.

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hey guys!

i ended up putting different jets in it.. i had a 20 pilot and 330 main before, now have a 17.5 pilot and 290 main. 3600 ft, 50-60 degrees, anywhere from 30% humidity- 100%. still a little bit rich, but much more crisp and more power. i also switched to a b8es spark plug. i cant find a needle anywhere so far, suzuki discontinued it. they also werent much help with the jets, i ended up going to a bike shop up here in hickesville and surprisingly they ended up having them.

specifically heres the problem: it bogs down a little at mid rpm still, but not as bad after changing the jet. if you twist the throttle a bit more it picks up. i might try a 280 jet and see how that is next time i go into town. also switched to bel-ray synthetic! i use the bike for woods and fsr roads, no MX or track or racing up here! went over everything again: reeds seal good, air filter cleaned and not over oiled, ignition, fuel all good.

as for the noise pollution... any time is 2 stroke time up at the cabin! so many trees, neighbours are always chainsawing away or ripping on their bikes. a few less deer standing on the road would be a good thing in my opinion as well. still looking for a silencer, up here when you want a part for something you dont go to the store, you go to the scrap yard and hunt around! theres usually a few snowmobiles, old bikes, etc in the pile so hopefully one day i can grab a silencer that will fit, for free!

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