81 Suzuki rm125 stator problems?

Hey! I was wondering if anyone had an answer to my question. I have an old 81 rm 125 that did run great. The other day I was riding and all of a sudden it seemed like I fouled a plug. It spit and sputtered and would not rev hi at all. Twist back the throttle and it would backfire and shoot flames. I got the bike home and changed the plug. The new plug did not fix my problem. I thought maybe that plug was bad too, so I put another one in. same problem. The bike will run and idle fine but like i said give it gas and it will backfire and bogg down. It is hard to start now. I am thinking I have a stator problem or if it has points they may be bad. It almost seems like the spark isnt in time or something. The bike has plenty of compression and im sure theres no carb problems. One time it took a spell and did rev fine, but the next throttle pull back was the same problem. But if anyone knows what it is or what steps I should take to narrow this problem down I would gladly appreciate your input.

Thanks A Lot, Matt

I don't hear about it happening to 125's very often, more often with big bores like YZ490's(mostly), CR500's, CR480's and KX500's. Anyway, to the point, pull the magneto off and see if the woodruff key is still intact and not sheared off. Sometimes a back fire can actually cause such a shock that the key will shear right off, and put your bike way out of time. Lucky for you it's only a 125. If that happens with a big bike the kick back can literally break your foot or leg when trying to start the bike.

Another thing could be that your coil just bit the dust... Or maybe it has this problem I've heard of. Sometimes when a bad coil is cool it will appear to work fine. When it gets hot it will stop charging and discharging, or just discharges with greatly reduced spark output.

Or like you said the points could be bad. If it has points at all... I don't know, I would think it has CDI but it's your bike so you know better than me. It sounds almost like the timing is so retarded that the spark plug fires at just about the time the piston is opening up the exhaust port. I don't know if it would even be possible for that too happen though, normally I think the ignition would jump to an advanced position not a retarded position.

Yea, It's CDI, Just took it apart. Were would that key be located exactly. I really dont know what it looks like. I did take the magneto off, but the flywheel i left on. Oyeah, i did try to start it today and it ran fine for maybe a minute then started back again. and oyeah, the kickback does hurt. lol

Nevermind, i know where its at, i havent taken that part off yet just the electronic part around it. But if the key is sheard off then wouldnt the magneto turn? it seems to be tight cause i sure as heck cant get it off.

It's a tight enough fit on there that it will hold in place when trying to turn it by hand. The key is made of aluminum, they're meant to break to keep from breaking your motor instead. A lot of big bore bike owners ride around on bikes with sheared keys and don't even realize it. It's a flawed system, they don't necessarily incapacitate the bike as ideally it should... It always causes problems when they break though. If that turns out to be the problem, when you replace the key you should do this.

Buy some valve grinding compound, apply a fair amount to the flywheel/stator shaft then hand press fit the stator back onto the shaft. Do not install the key, and do not put in the retaining bolt. Put the bike in gear with the rear wheel firmly planted on the ground so that the motor cannot spin. Then proceed to "lap" the shaft to fit the inside shape of the stator perfectly(It pry takes little elbow grease). Next pull the stator off remove the excess compound and clean the parts thoroughly. Re-install the key and tighten the retaining bolt to factory torque specs. It creates a tighter bond and greatly reduces the chance of the key shearing again. I think I've heard of people using some low grade lock tight in conjunction with this process, but don't quote me on that.

I never had a two stroke really kick back at me... At least not hard. I'm used to it though coming from four strokers that kick like mules when they get hot, especially after a stall or bail.

I'm just talking from stories I've heard about the horrors of a open class two stroke back fire kick back. I am a little scared just waiting for it too happen to me. Maybe these guys are just wusses though... The kick back from my old WR250 wasn't even as bad as my XR100 when it kicks back.

Hey BTW, how does that 81 stack up against modern 125's? I always wanted an 81 RM125 or 250 ever since Dirt Bike Magazine inducted it into the Hall Of Fame in like 99 or 00(or maybe 01).

The person that owned the bike before me rebuilt it about 2 years ago. New top end and also some transmission work done. Anyways he spent 600 bucks to get all the work done. It set for 2 years in a building. I couldnt ride it before I bought it so i just took a chance and bought it for 150 bucks. Got it home cleaned the tank, changed the oil and made sure it had coolant and it started 2nd kick. I warmed it up a little and took off. I didnt know what to expect because i never rode an old bike either. It suprised me. With 11/50 tooth sprockets it still lacks bottom end. Which im sure older bikes did anyways but if i ever get all the kinks worked out ill get a bigger rear sprocket. Theres actually not much difference in power between it and newer 125's. and of coarse feels a little smaller than newer ones. My cousin ownes a 2000 rm 125 and I told him we need to drag. But when i get this electrical problem fix which i think its the coil now, we will. Ill let you know the results .