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Suzuki RM125 model history
Air-cooled models, 1975—1980

I have tried to tell the RM 125 model history on this page as I know it. This page is still under construction. I would be grateful of any contributions — sales brochures, magazine ads, magazine articles, pictures, specs, facts, corrections etc. Please scan the material in JPEG format (large enough that all the details are visible) and send them to me. Please tell me the source and the publication date if possible. If you send me pictures of your own bike, please follow these instructions.

  

Suzuki 1975More Suzuki models from 1975
1975 Suzuki year code: M

Suzuki introduced the RM series of motocross models in 1975, these replacing the TM models. The range quicly stretched out from 50 to 400cc and became very successful. A few years later the Full Floater swingarm was introduced and water-cooled engines came along in 1981 — and the developement of the RM models continues even today.

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.
'75 RM125MRM 125 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 (190 lbs)
Engine type: Air-cooled 123 cc single-cylinder 2-stroke piston valve. 23 hp/ 10,500 rpm, 1..7 kg-m (12.3 ft-lbs)/ 9,500 rpm

Click on the image for larger format.
'75 RM125SRM 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

Click on the image for larger format.
Here's even larger picture.
'75 RM125SThese two pictures or the rare RM125S were sent to me by Allan Tucker, Barbados.
“You can see quite clearly the CDI box mounted on the steering column on the bike and how the hand made pipe looked as well as the non tall cap carb. The small dents in the stinger bulb were there when I bought the bike, but the bigger impression in the pipe lower down is for the kick starter to pass when starting,” Allan says.


There's more info of Allan's RM125S on the Visitors' Suzuki pages.


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

Source: U.S. Suzuki Motor Corp. Service Bulletin RM-1 (May 1, 1975)


Alan Tucker sent me some RM125S spec carb data to add to this page against the standard RM125M. Alan writes: “Just look at the size of this thing and its main jet compared to the M models tiny 28mm one with a #180 main, even the faster A model only had a 32 mm carb when it was released, but the same size 280 main jet was retained.
In the RM125S carb the two floats were separate from the arm, riding up and down on two vertically mounted brass shafts pressed into each side of the bottom of the float bowl. They also had short pins fixed onto the side portion that touched the separate arm unit to register float level. For some unknown reason Suzuki choose to use bright PINK poly hoses for the overflow tubes on the S model, you could not miss the colour of these hoses.”

Mikuni 28
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)

Mikuni VM34SS
Bore: 34 mm
Main jet: #280
Pilot jet: #35
Needle jet: P-3
Slide needle: 6DH3-3rd
Slide cutaway: 2.5
Air screw setting: 1.0 turn out
Float level: 9.1 mm
ID number: 41700

Suzuki RM125B RM125 '77

Suzuki 1976More Suzuki models from 1976
1976 Suzuki year code: A

 
The RM125A with six gears was distinguishable a mile away, the first Suzuki motorcrosser with an up-swept exhaust pipe. The bike was very fast and competitive. In 1976 there were two different models available; the RM125A and the (rare) RM125S. The models had the same piston displacement but were quite different motorcycles. While the RM125A's engine had reed valve, the RM125S piston valve. It also had different piston rings, larger carburrettor and different gearbox etc. The S model had a 5-speed gearbox. There were differencies even in the suspension. The most significant difference between the models was that the RM125A had a high-drawn exhaust pipe, while the RM125S had it drawn under the engine.

The 1976 RM125S and the 1975 RM125M were almost identical machines. Probably the RM125M had a welded on muffler, and the RM125S muffler was removable by a top and bottom spring. There were some carburetor changes, and a gain of three horse power in the S over the M model.

In Australia the RM125A came very late and weren't available until the 1977 Motocross season.

I haven't managed to find a picture of the RM125S anywhere so I used a RM125M picture instead. I will replace the picture as soon as I can find one of the S model.
 
'76 RM125ARM 125 1976
Overall Length: 2,075 mm (81.7 in)
Overall Width: 840 mm (33.1 in)
Overall Height: 1,122 (44.2 in)
Ground Clearance: 265 mm (10.4 in)
Wheelbase: 1,395 mm (54.9 in)
Dry Weight: 86 kg (190 lbs)
Engine type: Air-cooled 123 cc single-cylinder 2-stroke Reed valve. 26 hp/ 10,500 rpm, 1.81 kg-m/ 10,000 rpm.

Click on the image for larger format.
'75 RM125SRM 125 S 1976 (in some countries)
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

Click on the image for larger format.
I found the picture from the American Historic Racing Motorcycle Association website.

1976 RM 125-A specifications (Finland)
Engine Type: Air-cooled single cylinder two-stroke
Cylinder Volume: 123 cc (7.5 cu-in.)
Power output: 26 hp/ 10,500 rpm
Torque: 1.81 kpm/ 10,000 rpm
Compression ratio: 7,5 :1
Bore x stroke: 56.0 x 50.0 mm (2.20 x 1.97 in.)
Intake system: Suzuki Power Reed valve
Ignition: Suzuki PEI (Pointless Electric Ignition)
Combustion chamber shape: ”Squash”
Rinse channels: 6
Piston rings: ”Keystone” steel ring, 1.2 mm
Carburetor: 32 mm
Exhaust pipe: Drawn above the engine
Air filter: 79 x 163 mm
Fuel/oil mixture: 20:1 (5%)
Gear ratios  
    1st gear: 28/12
    2nd gear: 28/16
    3rd gear: 24/17
    4th gear: 25/21
    5th gear: 23/22
    6th gear: 22/23
Primary drive ratio: 63/17
Final drive ratio (chain): 57/14
Gear shifting: Gear
Clutch: 7 composition plates, 6 steel plates
Frame: Chrome molybdenum profile
Front suspension stroke: 200 mm (7.9 in.)
Rear suspension travel: 212 mm (8.3 in.) ”Tru Track”
Swinging arm length: 515 mm (20.3 in.)
Streering angle (left to right): 60 degrees
Wheelbase: 1,395 mm (54.9 in)
Ground clearance: 265 mm (10.4 in)
Dry weight: 86 kg (189 lbs)
Footpegs: High indented, return spring
Fuel tank capacity: 6,0 liter incl.reserve (1.6 US gal, 1.3 Imp gal)
Side cover: With a hole for air-intake
Front tyre dimension: 3.00-21 4PR
Rear tyre dimension: 4.10-18 4PR
Recommended retail price: 5,490 FIM (Helsinki, Finland 1976)

1976 RM 125-S specifications (Finland)
Engine Type: Air-cooled single cylinder two-stroke
Cylinder Volume: 123 cc (7.5 cu-in.)
Power output: 26 hp/ 10,500 rpm
Torque: 1.79 kpm/ 8,500 rpm
Compression ratio: 7,5 :1
Bore x stroke: 56.0 x 50.0 mm (2.20 x 1.97 in.)
Intake system: Piston valve
Ignition: Suzuki PEI (Pointless Electric Ignition)
Combustion chamber shape: Hemisphere
Rinse channels: 6
Piston rings: ”Keystone” cast iron ring, 1,5 mm
Carburetor: 34 mm
Exhaust pipe: Drawn under the engine
Air filter: 62 x 154 mm
Fuel/oil mixture: 20:1 (5%)
Gear ratios  
    1st gear: 30/14
    2nd gear: 27/17
    3rd gear: 25/20
    4th gear: 23/22
    5th gear: 21/23
    6th gear: -
Primary drive ratio: 61/18
Final drive ratio (chain): 60/14
Gear shifting: Pivot
Clutch: 6 composition plates, 5 steel plates
Frame: Steel profile
Front suspension stroke: 190 mm (7.5 in.)
Rear suspension travel: 200 mm (7.9 in.)
Swinging arm length: 445 mm (17.5 in.)
Streering angle (left to right): 61 degrees
Wheelbase: 1,360 mm (53.5 in)
Ground clearance: 245 mm (9.6 in)
Dry weight: 86 kg (189 lbs)
Footpegs: High indented, return spring
Fuel tank capacity: 5.0 liter incl.reserve (1.3 US gal, 1.1 Imp gal)
Side cover: No air-intake
Front tyre dimension: 3.00-21 4PR
Rear tyre dimension: 3.50-18 4PR
Recommended retail price: 5,490 FIM (Helsinki, Finland 1976)


Suzuki 1977More Suzuki models from 1977
1977 Suzuki year code: B


The only things that stood out to tell the B model apart from the previous model was the leading front axel and the “muffler on the end of the exhaust was a fraction longer. Inside the engine the bore and stroke was changed to a slightly smaller bore with a longer stroke to help bottom end performance. It was now a square 54 mm x 54 mm bore engine.

In Australia the RM125B came very late and weren't available until the 1978 Motocross season.
 
Suzuki RM125B RM125 '77RM 125 1977
Overall Length: 2,060 mm (81.1 in)
Overall Width: 840 mm (33.1 in)
Overall Height: 1,120 mm (44.1 in)
Ground Clearance: 300 mm (11.8 in)
Wheelbase: 1,405 mm (55.3 in)
Dry Weight: 88 kg (194 lbs)
Engine type: Air-cooled 124,8 cc single-cylinder 2-stroke eed valve. 26.5 hp/ 10,750 rpm, 1.82 kg-m/ 9,500 rpm.

Click on the image for larger format.

1977 RM125B specifications (International)
Engine type: Air-cooled single cylinder two-stroke
Cylinder displacement: 123 cc (7.5 cu-in.)
Intake system: Suzuki Power Reed
Bore x stroke: 54.0 x 54.0 mm (2.13 x 2.13 in.)
Compression ratio: 8.0 :1
Carburetor: Mikuni VM32SS
Air cleaner: Polyurethane foam element
Clutch: Wet multi-pkate type
Transmission: 6-speed constant mesh
Gearshift pattern: 1-down, 5-up
Starter system: Primary kick
Final drive: Chain
Ignition: Suzuki PEI (Pointless Electric Ignition)
Front suspension: Telescopic, pneumatic / coil spring, oil dampened
Front suspension stroke: 230 mm (9.1 in.)
Rear suspension: Swinging arm, gas / oil dampened
Rear suspension travel: 224 mm (8.8 in.)
Front brake: Drum brake
Rear brake: Drum brake
Front tyre dimension: 3.00-21 4PR
Rear tyre dimension: 4.10-18 4PR
Fuel tank capacity: 6.0 liter incl.reserve (1.6 US gal, 1.3 Imp gal)
Color: Yellow



Suzuki 1978More Suzuki models from 1978
1978 Suzuki year code: C
 
An aluminum swing arm was introduced for the 1978 year's model.
Recommended retail price (Japan) in 1978: 280,000 Yen
 
Suzuki RM125 RM-125 RM125CRM 125 1978
Overall Length: 2,060 mm (81.1 in)
Overall Width: 840 mm (33.1 in)
Overall Height: 1,120 mm (44.1 in)
Ground Clearance: 300 mm (11.8 in)
Wheelbase: 1,405 mm (55.3 in)
Dry Weight: 88 kg (194 lbs)
Engine type: Air-cooled 123 cc single-cylinder 2-stroke, piston and reed valve. 26.5 hp (19.5 kW)/ 10,500 rpm, 18 Nm (1.82 kg-m)/ 9,500 rpm.

Click on the image for larger format.
Here's even larger picture.
Suzuki RM125SRM 125 1978
Overall Length: 2,060 mm (81.1 in)
Overall Width: 840 mm (33.1 in)
Overall Height: 1,120 mm (44.1 in)
Seat Height:
Ground Clearance: 300 mm (11.8 in)
Wheelbase: , 405 mm (55.3 in)
Dry Weight: 88 kg (194 lbs)
Engine type: Air-cooled 123 cc single-cylinder 2-stroke, Reed valve. 26.5 hp (19.5 kW)/ 10,500 rpm, 18 Nm (1.82 kg-m)/ 9,500 rpm.

Click on the image for larger format.
Here's even larger picture.

Suzuki 1979More Suzuki models from 1979
1979 Suzuki year code: N

 
Recommended retail price (Japan) in 1979: 255,000 Yen
 
Suzuki RM125TRM 125 1979
Overall Length: 2,125 mm (83.7 in)
Overall Width: 845 mm (33.3 in)
Overall Height: 1,225 mm (48.2 in)
Seat Height: 950 mm (37.4 in)
Ground Clearance: 340 mm (13.4 in)
Wheelbase: 1,440 mm (56.7 in)
Dry Weight: 86 kg (189 lbs)
Engine type: Air-cooled 123 cc single-cylinder 2-stroke reed valve. 26.5 hp/ 10,750 rpm, 18.4 Nm/ 9,500 rpm.
No image available for the moment.
No image available for the moment.


Suzuki 1980More Suzuki models from 1980
1980 Suzuki year code: T

'80 RM-125 RM 125RM 125 1980
Overall Length: 2,125 mm (83.7 in)
Overall Width: 845 mm (33.3 in)
Overall Height:  1,225 mm (48.2 in)
Seat Height: 950 mm (37.4 in)
Ground Clearance: 340 mm (13.4 in)
Wheelbase: 1,440 mm (56.7 in)
Dry Weight: 88 kg (194 lbs)
Engine type: Air-cooled 124 cc single-cylinder 2-stroke, Reed valve. 27 hp (19.8 kW)/ 10,500 rpm, 18.1 Nm/ 10,000 rpm.

Click on the image for larger format.




More: Suzuki RM125 1981 on


More: Suzuki RM125 brochures

More: Suzuki RM-RMX series


More: All Suzuki models


Sources: Suzuki Motor Company etc.

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