I have some older RM125 questions...

[wasted]

my brother just bought a 1990 RM 125(he owned a '98 YZ125 up until a couple years ago, and a '94 CR125 before that), he hasnt had it long and hasnt ridden it much, but the thing is a dog... its by far the slowest 125 either of us have ever ridden...
it has an fmf pipe, aftermarket aircleaner(not sure which) with the lid removed and a few tooth bigger rear sprocket...
according to the previous owner it was just recently rebuilt, it starts on the first kick everytime and after we messed with the jetting some it runs good, but something just doesnt seem right, the thing has no power to speak of... it hardly wants to even pull itself to get going, has no bottom end, has a little bit of a hit in the upper midrange, and then does nothing but make noise and vibrate on top...
it revs up alright and accelerates fairly decent once underway, but its like there is no power at all to the acceleration... just motion... and it doesnt take much sand or mud to sap what little power it has(so trail riding it is a pain)
even where it has excellent traction it wont pull the front tire off the ground in anything but first gear and even then you have to use the clutch and MAKE it do it...
I'm not firmiliar with RM's of that time period and never really dealt with them, but with all the stuff done to it I would think that it should go pretty decent...alot more than it does... where these things just naturally doggy, or is there maybe some inherent problem that they had that I should be looking at?
I dont know if any porting has been done, but we pulled the cover off and the exhaust valve actuator arm and valve seem to be working fine, we didnt dig into the actual valve yet though, thats next on the list, along with a topend rebuild(so WE know its recent)... anyone know if there were any problems with these valves that I should be looking at?
something has to be done or the bike has to be sold and something else bought...
I've ridden 80's were faster than this thing, its absolutley no fun to ride as it is...

 

[Can Can Kev]

is the power valve stuck, make shure it is operating properly because a stuck open or close power valve can turn a screamer into a dog...

 

[pace]

Yup. And I'd probably not trust the previous owner's claim of a new topend. What was the condition of the air filter when you acquired the machine? If I were in your situation I'd pull the entire topend for inspection. Also replace the tranny fluid and coolant while you're at it..

Let us know what you find.

-Pace

 

[Mike R.]

Before you do as the previous post mentioned

Check the Compression it alone will give you a good idea of how tight the top end is!

 

[viking20]

It probably isnt that worn , if it starts first kick, but I would check both the top-end and powervalve like the other guys said....Ive seen the tube crack in the silencer on older bikes several times , tilting , and block itself so theres almost no passage through the silencer . Ignition and reed problems would probably make it hard to start too , so I would start with the other things....It could be the piston is in backwards or something, you never know untill you check it on a used bike.

 

[dalton125]

I have a recently completely rebuilt 89 Rm125 and this thing is a beast. The only thing I put aftermarket on it was a Profire coil and a PWK 35 airstriker Kehien carb and this thing would easily throw me off out of the hole and it hits hard and revs to the sky on the top end. In my opinion there is something wrong with the top end. I used to have and bought it new a 90 RM125 and it rode and felt very similar to this older 89. If I remember correctly there is not a lot of difference between 89 and 90.
Oh by the way the airfilter lid is off of mine as well and I have never had any problems with that. Dalton125

 

[haagendoss]

wasted... did you ever find a solution to your rm problem? my 90 rm 125 is having almost the same problem. hard starts, no bottom end to speak of. will not pull the wheel AT ALL!!

 

[2-Strokes 4-ever]

Have a 98. Yours shouldn't be such a dog. They're not known for much low-end, but should rip once you hit mid-range. Your problems could be a number of things.........but DO make sure there is tension on the powervalve tension spring. More tension....more low end, and less tension...valve opens sooner hurting low end but making strong top end. Not to descriminate or anything, but... make sure you're not "waisted" when doing repairs.

 

[haagendoss]

but DO make sure there is tension on the powervalve tension spring. More tension....more low end, and less tension...valve opens sooner hurting low end but making strong top end.

the tension spring.. is this on the left side outside of the jug? if i remember correctly, a circular disc or something? i'm not really sure...

it has a solid top-end, no problems there. but i would still expect to have some good bottom end torque. For instance, stopping on even a slight grade will cause me to have to feather the clutch to just get the thing rolling. THANKS!!!

 

[2-Strokes 4-ever]

Yes, it's the dial on left side/front of cylinder. Maybe someone else can clarify this since I'm too lazy to go and take my son's 125 apart. You can remove knob (two screws) and see how knob fits into spring. If I remember you tighten the tension 1 turn and line dial up with mark. If there's no tension on spring, the valve opens too soon and low end power is total dog. But keep in mind that there isn't much low end in that bike when adjusted properly either. Just get used to abusing the clutch. It's amazing how you can do little things to improve the low end of that bike too. I used to race it in H.S. and little tricks like adding 2-3 more exhaust washers into cylinder before pipe goes on will make it a little torquier...low end reeds help...advance the timing just slightly...And we took I think 8 thousanths off the base of the cylinder. Got these tips from Bill's Pipes back when they did a lot of work with Team Suzuki. Even still...get used to measuring the wear on your clutch plates often. Never had a bike that handled as sweet as that 125!!! But I've gotten lazy in my old age and prefer not having to ride so aggresively...(went 250)

 

[haagendoss]

thanks for the help!!! i appreciate it. i'll check that out... i just bought new sprockets and chain to take teh ratio to 12/53 which should help a lot. i'm also looking at boyesen low-tens. reeds and an fmf silencer when the funds will allow it :-) Yeah just replaced clutch fibers last fall, it's just makes me cringe everytime i have to slip the clutch just to make it up a hill... we'll see if the new gearing helps, along with checking the tension on teh power valve... the 125 is one tight bike though!!! again, thanks for all your help!!!

 

[wasted]

wasted... did you ever find a solution to your rm problem? my 90 rm 125 is having almost the same problem. hard starts, no bottom end to speak of. will not pull the wheel AT ALL!!

no, I never did figure it out, I own that bike now actually, I trade my brother my '94 CR250 for it(the things you do for family :think: ) and I havent touched it since... its just been sitting in the back corner of my garage...

its funny this was brought up actually, I just tore the motor out of that bike and took the top end off the other day...
everything was fine inside, including the power valve, I found mine had a sleeve pressed into it though so I'm going to have to check out what kind of work was done to the valve, I did notice that it looks like it may be messed up some and I may have to do a little reshapeing to it but I didnt have time to really look at or mess with anything yet...
I'm going to give it a good rebuild, do some work on the valve if it needs it and see if that helps...

like I said, I'm not firmiliar with the '90 RM125, I know I had that thing jetted up and down every which way, I also cranked the powervalve adjuster to every position possible and I couldnt get any power out of it, but maybe a good rebuild will change that, we'll see this spring...


and no 2-strokes 4-ever, I'm not wasted when I work on my bikes, although sometimes they could(and do) force to me drink...

 

[haagendoss]

well i'm going to put a new ring in and make sure the powervalve isn't gummed up or anything, check the tension and see what happens. i'll let you knwo if i find anything!!!

 

[haagendoss]

UPDATE!!
The 125 is running better than it ever has! If anyone is having problems similar to those in this forum i'll explain what i did. Mind you it still doesn't have a lot of low end but it is considerably better. First step was a complete top end rebuild, all parts from pitposse.com (excellent prices and excellent service). I was just going to replace the ring because it has been less than a year since my last top-end, but i ended up buying an extra piston anyway... rebuilt top-end,went from stock gearing (13-50 for 1990 model) to 12-53 with a new DID 520 chain, and new NGK B9 Iridium plug.

When i got the thing all back together i couldn't get it to start. (i had been having trouble with it starting before the rebuild). After pushing it down the hill and popping the clutch she sputtered and started. long story short, when it would cool down it would go back to hard starting, to the point that i could not start it at all without pushing it. I had checked and cleaned the powervalve when rebuilding, etc. I took the carb off and soaked in carb cleaner, cleaned the reeds and following advice from someone here at dirtrider, put a small piece of teflon tape around the spark plug before putting her all back together. Got it together kicked it with full-choke and she fired first kick. I've started it several times in the last two days and it has started every time! the new gearing is near perfect for the type of riding i do (mostly trails and hills). I couldn't hardly pull the wheel even in first before the change, and now it will pull in first and shifting to second!!!