1979 rm125 tips

slomoto
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slomoto
Edited Date/Time 3/10/2014 6:12pm
just picked up a 1979 RM125 does anyone have any tips or hop ups that I should try?
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xnationalwrench 3/2/2014 5:51pm
3/2/2014 5:51pm Edited Date/Time 3/2/2014 9:14pm
If I remember we used to shorten the head pipe 6mm, mill the head .020" and replace the stock reed with a fiber reed (FMF). It did a pretty good job at CMC Pro races.
slomoto
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slomoto 3/2/2014 8:13pm
3/2/2014 8:13pm
thank you, and if anyone else has tips or tricks or recommedations I would appreciate them
xnationalwrench 3/3/2014 8:25am
3/3/2014 8:25am
Oh yeah, we also switched to a slightly thicker motor mount plate (front of the engine) made of 7075 aluminum and reinforced (gusseted) the foot pegs which worked well and never bent or broke a foot peg. I also had my brother who was welding for Rich Thorwaldson go over the welds on the frame and added a gusset plate to the bottom frame rails were they tied in to the down frame.
MaxPower
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MaxPower 3/3/2014 9:11am
3/3/2014 9:11am
If you have the engine apart use a solid 78 rm counter shaft back in its place. Same for the clutch arm that goes down into the case. Early Suzooks had issues with main bearings spinning in the case. If yours seems loose upon reassembly press's bearing in with a shim Around it. Red Loc Tite never seemed to work for me. Although never use red on your side number plate screws. You will have to drill them out. The roller on top of the swingarm can be replaced with a solid Teflon block. I think it was the 79 RM that had a solid black wire coming out of the CDI that was the rev limiter. I remeber clipping it one of my bikes. I think it was the 79. Put a bullet connector on it to reconnect it if it doesn't do anything. If you put a bigger carb on watch the float bowl clearance . It's easy for the bowl to hit the case and shake the fuel up. I had a 78 RM silencer on mine. Mostly because the stocker was so long. 78 RM125 silencers get big dollars now. Stay with a 428 chain that came on it if you can. They changed over in 1980. I never have done it but I think it's Wiesco that goes up to a 7th over bore. You can get over 131cc. None of this is in stone. I'm spouting info from over 30 years ago that hasn't been touched in my brain since then. I like the mods Xwrench told you. I'd do them. But run a good fuel to keep the pings away . It's a simple bike to work on and very reliable for a 125.

I remember I really liked my friends 78 rm125 power. If I had a 79 today I would experiment with a 78 black box just for the hell of it to see if that made the difference I liked

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yzvet426
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yzvet426 3/3/2014 12:08pm
3/3/2014 12:08pm
MaxPower wrote:
[b]If you have the engine apart use a solid 78 rm counter shaft back in its place. Same for the clutch arm that goes down into...
If you have the engine apart use a solid 78 rm counter shaft back in its place. Same for the clutch arm that goes down into the case. Early Suzooks had issues with main bearings spinning in the case. If yours seems loose upon reassembly press's bearing in with a shim Around it. Red Loc Tite never seemed to work for me. Although never use red on your side number plate screws. You will have to drill them out. The roller on top of the swingarm can be replaced with a solid Teflon block. I think it was the 79 RM that had a solid black wire coming out of the CDI that was the rev limiter. I remeber clipping it one of my bikes. I think it was the 79. Put a bullet connector on it to reconnect it if it doesn't do anything. If you put a bigger carb on watch the float bowl clearance . It's easy for the bowl to hit the case and shake the fuel up. I had a 78 RM silencer on mine. Mostly because the stocker was so long. 78 RM125 silencers get big dollars now. Stay with a 428 chain that came on it if you can. They changed over in 1980. I never have done it but I think it's Wiesco that goes up to a 7th over bore. You can get over 131cc. None of this is in stone. I'm spouting info from over 30 years ago that hasn't been touched in my brain since then. I like the mods Xwrench told you. I'd do them. But run a good fuel to keep the pings away . It's a simple bike to work on and very reliable for a 125.

I remember I really liked my friends 78 rm125 power. If I had a 79 today I would experiment with a 78 black box just for the hell of it to see if that made the difference I liked
It's funny that you mention that. I'm working on a 79 RM 400 engine.I replaced the bearings and for separate issues I 've had to pull the cases apart a few times (not smooth enough rotation). Each time the Left side main bearing comes off with the crank.
MaxPower
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MaxPower 3/3/2014 1:38pm
3/3/2014 1:38pm
I don't know what the deal is with Suzuki that they didn't make bearing bores tighter or do whatever it took to make sure the mains stayed put. My friends 81 RM250 was the worst. With my RMs I have tried punching dimples into the bearing seat and Red Tite and as I got more time on the bike the bearing would spin and I'd have crank play. I haven't thought about it until now, but maybe there is a way to tap a hole for a set screw against the outer race as a solution

The reason I had mentioned about replacing the countershaft with a solid 1978 part is that I've seen 3 79 RM125s actually break a countershaft . The chain was tightened correctly too.

Did you get a crank for your RM400? I just came across someone that replaced the 400 rod and bearing with a combination of new parts from another engine . I think it came out of a Polaris or something. If you need it I'll search it out

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