Silencing the RM125M

[Graeme M]

Given the TM is apart getting the CR125 beater treatment, I decided to try the TM's Circle F pipe on the RM. Turns out it bolts right on. My question then, to the TM125/RM125M/S gurus out there, is - what's the chances that this pipe will work OK with a pretty much stock RM125M engine?

[cyclegod]

Very good chances, Retro Rocket are the only ones making a '75 RM pipe but I believe this to be for the "S" kit engine, an "M" is closer to a TM any way

[Doc]

agreed, it'll work fine Graeme. I've a stock TM125 pipe on my RM125S TM and it fairly honks. Now looks like it's coming to CD5 also 

[Graeme M]

Excellent - I figured it would be fine. I am planning to go the Circle F pipe and rubber bungs in the fins, that should tame the noise a bit.  Then send off for another Circle F for the TM and I am away. Altho I might just chase up Geoff M re a TM pipe, maybe he can whip me up one better suited to my need for lots of top end for the DT Nats...

[Freakshow]

i would be inclined to tune the pipe for torque (which wont be at high revs), build the arse end to get the power into the ground,  you use sprockets to carry top end :

[Graeme M]

Do you think? I don't know about that, my problem is outright power. A stock TM gives away between 5 and 10 HP over the modded CR125s that dominate vintage DT. What I am aiming for is hopefully 3-5 HP more over stock so I am a bit more in the hunt. The ACT track has a longish uphill section and a CR pulls my TM real bad up that. I don't expect to win no Aussie title, but I'd like to be up with the pack after my disastrous show at last year's Nats.

I'm not sure if I ever shared this, but my problems at the DT Nats at Wagga included:

Way too rich jetting. I ended up going back about 4-5 sizes to get it to run clean.
Way overgeared. I came back 2 teeth on the front to get it where I want it for ACT.
Front wheel installed incorrectly which led to bearings binding. Because my bro pushed the bike around and I only rode it, I didn't notice until we got home that it was like riding with the brakes on.
Standard 26mm carb.

No wonder the thing would barely move... I guarantee a better showing this year.

[Lozza]

I am looking at a CR and a TM barrel and from the simulator figures and what I see you will need far more than 3-5hp to keep up with any well sorted CR.If you are not nudging or over 30hp you will just be a little less behind.
Look here



Continue on

[211kawasaki]

Im with Doc, I have tried all manner of pipe on my TM and the std TM pipe is better in my view than the RM,m/s pipe and the 2 other "trick" after market ones that came with a bullshit wrap and did worse than standard.
I say find a TM pipe, muffler and all for best results - I kid you not; it has to be without a doubt the best mid range to top rather that nothing till the thing is screaming its brains out with the rest of them.

211

[Graeme M]

Now that IS interesting. So if Suzuki knew how to make good pipes, and the TM engine is gonna be modified (ports, ignition and carb) how would an RM125S stock pipe work? I scrounged up just such a thing the other day, though it's in bad shape and needs some help...

Lozza, I know that I would still not be in the ballpark with 25 HP, but I am hoping that would be enough to at least keep with the pack. My local knowledge will help a little and I know from the practice days that there are a couple of sections where I am actually pretty fast (hard to believe but true). Now, if I had a little more steam up the hill and could learn to brake later, I might be in there fighting. Which is all I am after...

[Doc]

After now riding them in both MX and DT my biggest issue with the TM and RM is me..poor starts..the guys on the hotty CR's get the jump and by the time I get mobile the gap is a little to large to be able to hook onto the rear of them. This gap didn't blow out that much once we all settled down and in the last it remained constant not giving away much at all over 5 laps. This was also running an oil track tyre that didn't have all that much traction in the tight turns. For me it's a case of need more ride time and practice, I feel the bike has the goods but I don't  I probably pick up about 3 or 4 HP over the average weight rider simply because I'm light. I never really liked the feel/attitude of the RM125M/S hence that's why I've fitted the motor into a something I do feel comfortable on..the TM 

[suzuki27]

Someone might know about the ignition timing to help-the right advancement might help with the rest of the work Swapping to the 250 CDI might also help,as I remember this being done on 79-83RM125,and it made them rev higher-something to kick around with someone who knows a lot more about engines than I do!.

[oldfart]

All this talk about Hp is a good thing , what about your body mass weight and fitness factor this should be good a 5 HP 

[Freakshow]

For what its worth i blew up a black box on my TM 250, i could only find a TM 400 one ( no idea what year model) and when you put it against my other tm250 with the normal Black box its seems to have more pull, i could just be dreaming and its just the bike has changed somehow since, but they are exactly the models etc, but it feels  differant in the way it revs and where it pulls even where it gets on the pipe on a DT track, i have no idea on the mX track but on the longer stuff it seems to run cleaner and pull longer.

so SUzi 27 may be onto something there, as usual i refer you to Lozza.

Old fart are you refering to your 'sprung 'weight  maybe go cammo that might lighten you up somewhat.

[Doc]

you've mentioned a very interesting point Freaky..

it's weird but in all my life I have never had 2 identical bikes that rode identically. never!

I firmly believe if you sort out the mismatching of ports and cases,gaskets, pistons and manifolds that the factory didn't bother with the gains will be surprising.

[Lozza]

Th 400 CDI would run more advance, but that all depends on the static timing on the stator Freaky.IIRC 250's are set to something like 2-2.4mm BTDC and 400's 3-3.2mm BTDC.Big bores don't need retard becuse they don't get to the rpm where it starts to be needed.A 125 runs static timing of something like 1.2-1.5mm BTDC so swapping to a 250 CDI is a retrograde step.Static timing should always be set with a dial indicator.An interesting test will be to see if Graeme's clutch starts to slip, especialy in top gear and if the brakes fade and seem under powered.
Funny that Doc because even at GP level riders have their favourite bike, I would hazard a guess that they are set up identical