Suzuki RM125 model history, 1975-1980

10 Apr 2015 | Author: | Comments Off on Suzuki RM125 model history, 1975-1980
Suzuki RM 125

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 RM125S.

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.

RM 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)

RM 125 S 1975

Suzuki RM 125

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

“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.

Suzuki RM 125
Suzuki RM 125
Suzuki RM 125
Suzuki RM 125


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