RM125S questions for the Guru's

[Doc]

2 questions put to me that I'm at a loss to answer

Was the 'porting' the same for both 125S and 125M?

Was there an engine number sequence designated specifically for the RM125S?

[albrid-3]

I was sponsored on a RM 125 S, and I was told that the S was much more developed than the M model, the  Rm S model was sold as an expert bike had a larger carbie and porting was more improved over the RM 125 M.

[pokey]

The S were hand ported wernt they doc?
if so you shouldnt see the sand casting

with the s being a rare bike and SFA of them finding thier way to the US of A records will be sketchy being an  half year bike.

my records show the S starting at 19800 but exact build numbers i have never been able to find. ED may have a few more clues seeing he has more than his fair share of the nice little things

[albrid-3]

RM 125 S 1975
Overall Length: 2,040 mm (80.3 in)
Overall Width: 860 mm (33.9 in)
Seat Height: 901 mm (35.5 in)
Ground Clearance: 245 mm (9.6 in)
Wheelbase: 1,360 mm (53.5 in)
Dry Weight: 86 kg (189 lbs)
Engine type: Air-cooled 123 cc single-cylinder 2-stroke piston valve. 26 hp/ 10,500 rpm, 1.79 kg-m/ 8,500 rpm

[pokey]

http://www.suzukicycles.org/RM-RMX-series/index.html?RM250-RMX250.shtml~isoraami



The first model version of the RM125 had "downpipe", the exhaust pipe placed under the engine. The TM125 was discontinued and instead came the RM125. When tested against the competition in the US market the RM125  was found not powerful enough to compete with the Honda CR, kawasaki KX and Yamaha YZ models and had to be quickly modified before mid year 1975. The model name to the revisited model was RM125S.

To make the bike faster Suzuki did some interesting alterations in the following areas of the engine: they reworked the porting of the cylinder barrel massively, all ports were opened significantly and they appeared to have been finished by hand when viewing the cylinder. The new hand built exhaust pipe for the RM125S was slightly larger in diameter and made of many rolled steel pieces welded together, not stamped with two londitudal folded seams like the M model. The stinger bulb was also welded on at the end of a slim diameter pipe with a stiffener rib above and below it to stop cracking where this pipe met the end of the expansion chamber.

The headpipe also still carried the OEM chrome exhaust collar, but now used extra "L" shaped  pieces placed under the bolt heads, these 'ears' each held one end of the springs that kept the pipe in place to the cylinder head.

The pistons skirt had two holes drilled into it to help cool the thin exhaust port bridge section as the new exhaust port was now quite wide, the head gasket material was also slightly different.

The S models Mikuni carburettor was also quite larger and didn't have the tall top cap as the M model, and the carburettor intake rubber/alloy pipe was also larger and carried an adapter plate. The new carb had increased jetting values and a special needle valve orifice with three extra angular drilled holes to allow fuel to bypass the lower needle valve body into the bigger float bowl.

The newer and bigger CDI unit for the S version was now mounted onto the front of the frame headtube with a bracket instead of in front of the aircleaner case as with the M, and finally the air cleaner case was altered to accomodate a bigger rubber connector boot. To let the owner know they had bought an 'S' model, the fuel tank had a decal affixed right below the filler opening that said RM125"S".

As noted, the power output went up to 26hp, and this was enough to allow it to run with the CR, KX and YZ models that were beating the M model. The S model only lasted for about four months (later in some countries, it was sold as a 1976 model at least in Finland) as the new A model was being tested for '76 and the S therefore never sold in large quantities.

[albrid-3]

1975 RM125M specifications

General
Length: 2,040 mm (80.3 in)
Handlebar width: 860 mm (33.9 in)
Footpeg height: 350 mm (13.8 in)
Ground clearance: 245 mm (9.6 in)
Wheelbase: 1,360 mm (53.5 in)
Seat height: 901 mm (35.5 in)
Dry weight: 86 kg (190 lbs)
Wet weight: 92.7 kg (204 lbs)
Front brake: 130 mm diameter
Rear brake: 130 mm diameter
Front tire: 3.00-21-4PR
Front tire: 3.00-18-4PR
Frame: Semi-dual cradle

Engine
Horsepower: 23 hp/ 10,500 rpm
Torque: 1,7 kg-m (12.3 ft-lbs)/ 9,500 rpm
Engine type: Two-stroke, air cooled, 6-port scavenging
Bore and stroke: 56 x 50 mm (2.20 x 1.97 in)
Displacement: 123cc (7.5 cu in)
Compression ratio (corrected): 7.4:1
Lubrication: Fuel and oil premix, 20:1 (5%)
Carburetion
   Bore: 28 mm
   Main jet: #180
   Jet needle: 5DP7-3rd
   Needle jet: P-4
   Cutaway: 2.5
   Pilot jet: #50
   Pilot air screw: 1 1/2 turns
   Float level: 25 mm (0.98 in)
Air filtration: Wet polyurethane filter
Exhaust system: Expansion chamber with external silencer
Starting system: Primary kick
Clutch: Wet, multi-plate type
Type of transmission: 5-speed constant mesh
Primary drive: Staright-cut gears
Primary reduction: 3.389 (61/18)
Final drive: #428TM chain, 126 links
Final reduction: 4.286 (60/14) Solid mount rear sprocket
Gear ratios
   Low 2.143 (30/14)
   2nd 1.588 (27/17)
   3rd 1.250 (25/20)
   4th 1.045 (23/22)
   5th 0.913 (21/23)
Ignition: PEI (same as TM125)
Spark plug: NGK B-9EV

Suspension
Front suspension: Telescopic fork, hydraulic damper
Inner fork tube poutside diameter: 35 mm
Front fork travel: 190 mm (7.48 in)
Front caster (from horizontal): 61°
Fork trail: 123 mm (7.48 in)
Rear suspension: Swing arm, hydraulic damper 5-way adjustable spring
Shock absorbers: Gas/oil type, forward mount, "lay-down" position
Rear wheel travel: 198 mm (7.80 in)

Capacities
Fuel tank: 5.28 liter (1.4 US Gal)
Transmission oil: 550cc (1.16 US Gal)
Front fork oil: 210cc per leg

[sleepy]

I had an S when I first went into Seniors and it was a rocket.

Also got a parts book that cover those models and they only list as being different the following.
Piston, carb, air filter, pipe and a bracket to mount the CDI in a different place.
Part number for the barrel is the same.

From my memory there was no hand porting to be seen inside the barrel on my bike.
Most obvious change was the pipe, it looked hand built rather than a pipe looking like a TM125 pipe.

[pokey]

Cycleguide 1975

This is a test that really highlights the pre 75 class with the new breed of mx bikes and a new era then follows. I rode my first real mx season on a 1975 RM125S and it was coool – big sand woops no longer held any fear, full throttle and just hit em hard!!! The RM125 tested here is the US version RM125M, the faster RM125S came to Australia



For Suzuki, the RM 125 is a giant leap forward. At long last, some of the racing technology that helped Roger DeCoster and Joel Robert garner a fistful of World Championships has found its way to the production line. But Suzuki’s ultra-conservatism, a trait that has characterized most of their motorcycles for some time, prevented them from winning this comparison. The stock RM 125 finished second solely because it didn’t have enough power to keep up with the YZ. But Suzuki is offering a factory kit for the RM, a $200 bolt-on affair consisting of a different pipe, a 30mm carburetor, a cylinder with more radical porting, and a piston with a higher intake cutaway. They put a kit on an RM and allowed us to try it during the comparison. Our conclusion: The RM would have won the test if the kit had been standard equipment. The trick parts make the Suzuki just about as fast as the YZ, and with its slight handling edge, would have made it The Japanese 125 motocrosser. It’s nice to know the kit is available, but it’s also hard to understand why they didn’t build it like that in the first place. The kit doesn’t make the RM any harder to ride, and adds about 10 or IS percent on the top end and mid range without taking much away from the bottom end. If you buy an RM, get the kit. It’s worth the money.

[Lozza]

biggest difference is the TM has a mere 2 large transfers and the S 6 smaller transfers.

[pokey]

RM125 port map from suzuki service bulletin

May 1 1975

[oldmxracer]

I lived 1/2 mile from the local Zuki dealer back then and don't remember an "S" model here in the States. All they did was put the kit (pipe, cylinder and carb?) on for guys who wanted to hop em up. But that's been a LONG time ago, eh?.?.?.

[saint]

Found this on Gumtree last week....................
Check out the trick pipe.

http://www.gumtree.com.au/s-ad/williamstown/motorcycles/super-rare-vintage-1975-suzuki-rm125s-rms125-suit-vmx/1066755332

[Doc]

Thanks for the info ppl.

I should be able to 'physically' confirm port changes with that port map thanks Pokey (providing my S barrel is stock )  There doesn't appear to be any radical port changes when looking but a mm here and a mm there isn't overly obvious to my uncalibrated eyes

Found this on Gumtree last week....................
Check out the trick pipe.

http://www.gumtree.com.au/s-ad/williamstown/motorcycles/super-rare-vintage-1975-suzuki-rm125s-rms125-suit-vmx/1066755332

Saint, that pipe is what could be called an UpsideDownpipe. The idea has never once occurred to me in the past 40 years

[pokey]

A while back Dodgee was building an M so he may know or have the port specs for that to compare it with.

From what i get from all the info above is there was only ever one barrel but suzuki hand ported them and in some markets sold it as a hop up kit. Australia who never got the hop up kits for any models actually scored the complete bike with hop up kit fitted and it was called the RM125S

[80-85 husky]

I was led to believe that the M models suffered from poor quality control in the factory in the bore to piston clearance area resulting in numerous seizures. the "s" was rushed out to cover these issues and the motor got a work over as well.....not sure how true this yarn is. the us mag story of "why did suzuki suddenly supply a much better barrel" seems a bit strange but hop up kits were a huge market in the US so I could see Suzuki working that market.

[bazza]

https://www.facebook.com/groups/444737422335541/
scroll down 5-6 photos to see nice restored suzuki 125

[OverTheHill]

had a genuine RM125S once, traded it on my year old YZ250C [airbag fork model], got more enjoyment out of 'that' bike than the 250 despite breaking the end off the crank [at the LH main], magnets grabbed the rotor in full flight which was fun when landing with a dead engine. Spent some time looking for spark lol. Big carb & big porting, great aircleaner set up. Another one i shouldn't have sold damn it.

[dodgee]

I had both M & S nos barrels , the only difference that i could see was the M had one more cyl fin at the rear , where the S had it removed to fit the adaptor for bigger carby.

[oldfart]

125 M carb  VM 28SS   Id # 28720      Timing  3.8mm
125 S carb  VM 34SS   Id  #41700       Timing  2.20mm

[Tim754]

Top two piccies show difference in M swing arm, the rest show parts only on S model.

[Doc]

I had both M & S nos barrels , the only difference that i could see was the M had one more cyl fin at the rear , where the S had it removed to fit the adaptor for bigger carby.

thanks dodgee.. basically the same is what I figured. Too lazy to get out the verniers

thanks to everyone for all the reference fodder also

[oldyzman]

I like the RM "S"
Brett

[80-85 husky]

ol mate got a job at b15 and left school. with his second pay packet he bought a 2nd hand montessa 125~ about a 73 I rekon. it went exactly 100 metres and exploded. in disgust and embarrassment, he got a loan and bought a new rm 125 s. what a machine for a bunch of kids on dax's and kwaka 75's...agi 100 yammies etc. great bike. he never raced it and dropped out of bikes after his first headj@b

[albrid-3]

ol mate got a job at b15 and left school. with his second pay packet he bought a 2nd hand montessa 125~ about a 73 I rekon. it went exactly 100 metres and exploded. in disgust and embarrassment, he got a loan and bought a new rm 125 s. what a machine for a bunch of kids on dax's and kwaka 75's...agi 100 yammies etc. great bike. he never raced it and dropped out of bikes after his first headj@b

Now that was funny.

[pmc57]

Here's a trio of the little monsters at last years CD10

[80-85 husky]

that first hdjob destroyed a lot of promising riding careers....

[Tim754]

And yet the Suzuki parts books I have appear to list no different barrel between the two I better look harder

[oldfart]

It's not very often you get to  see 3 nice clean Rm 125 S sitting next to each other.

[John Orchard]

Ok draggin-up an oldie but subject matter was not completed.

RM125M cylinder 12110-41001
RM125S cylinder  12110-41002

I just got an American listing for their kit '75 RM125's. If you find a 12110-41002 listed anywhere, check on the actual description, American Suzuki have the description wrong, it is listed as a TM125 piston.

I actually just bought a piston off ebay, listed for a TM125, not using the above number but it did have two part numbers on the box (12110-41731 & 12110-28753, the latter number is the kit piston for the S, all websites list it as a TM125 piston), it was $12, it arrived today, it is a kit 'S' piston, with .6mm ring grooves, obviously the dealer kind of knew it would not fit a TM (although it will with .6mm rings).

So, I now have the part number for RM125S piston rings, again, American Suzuki have the description wrong, they are listed for TM125 ! but I figure the ebay selling dealers might know they won't work on a standard TM piston but they don't know what, so they are super cheap, I just bought a set for $10 :-)

[sleepy]

I just had a look in my RM125 M,S,A&B parts book and the 11210-41001 part number is before frame number 18508 and the other note says for the 002 barrel use 13125-28701 inlet gasket. In the back of the book there is a section for parts that are different for the "S" and the barrel isn't mentioned. The only things different are the Carb, airbox, piston(12110-41730), pipe and CDI bracket and wiring. Rings as well 12140-28740.
Happy to scan the "S" pages and send through if you want.
I've heard people say the S barrels were hand ported in the factory and the couple of S barrels I've seen did have the inlet port cleaned up pretty well but the parts book doesn't show it as a different part so without having an original M and S side by side I can't say. Could have been that part way through the M series the S barrel became fitted.

[John Orchard]

Go to 'Suzuki Racing Kit MX' page on Facebook, they have pics of the kit with American part number lists.

https://www.facebook.com/photo/?fbid=460318346283298&set=pcb.460318439616622

[sleepy]

Kit didn't come to Australia as the bikes were sold already kitted.

[pokey]

The barrels are yet another Suzuki Myth. Everyone including myself believed for years that the S was hand ported. I really dont know where this started but it has been confirmed by a member who builds great bikes in QLD and has/had both and they were originals. When asked he stated there was no difference with the M and S porting at all. You could likely search for the thread. Possibly more American marketing hype.

[John Orchard]

Go to the link, see what you think.

[pokey]

 The man to ask is Dodgee. You could try sending him a pm though he never was that comfortable with this style of communication and prefers phone calls. A conversation many years ago with Wayne Doc and myself  he says the porting is unchanged though the inlet may be larger to suit the bigger carb. Now another anomaly the parts book shows a 14 fin head which Wayne had and its listed for the M model only and a 15 fin for the S. Another to ask would be PERMS . Pete owns the very pretty S that regularly scores top marks at Conondale classic show n shine. But the guru of Suzuki has to be Doc, if he doesnt know then it didnt happen. best of luck with the investigation.

[sleepy]

Go to the link, see what you think.

The kit does obviously come with a barrel that has a large inlet port but is it any different to local "M" or "S" barrel? The parts book does list a different barrel after a certain frame number which my guess would be the same as the local "S" and some of the "M". The kit may have been manufactured for the early batch of "M" models that may or may-not have had smaller inlet ports.
If you can tell from the photo what the inlet port size is as a comparison the "S" barrel I have sitting here in front of me has a 35.6mm inlet port and has been highly polished and the transfer passages have been knife edged as well. . What I don't know is the polish factory or not but my guess is not. Those "S" pipes are a very nice thing and make a TM125 go quite a bit better.