Suzuki TM Motocross Models
Introduction:
Joel Robert was Suzuki’s first Motocross World Champion in 1970 winning the 250cc class and after this success Suzuki introduced a production motocrosser. The Suzuki TM400R was manufactured for the 1971 season and coincided with the signing of Roger DeCoster in October 1970. The following information traces the history of the Suzuki TM range and were possible have included original Suzuki brochures to help people identify and restore TM’s. These early Suzuki motocrossers are now a collectable machine as well as a reliable and competitive bike in the Pre-74 Classic Scramble events.
TM400R (1971)
Nicknamed the ‘CYCLONE’ the TM400R was the first Japanese production motocrosser to be mass-produced. The huge 82.5mm bore piston turned out 40 bhp at 6,500 rpm and along with the fan-finned cylinder head it had a compression ratio of 7.3 : 1. The crankshaft halves were not full circle type as fitted to most two-stroke engines and made the engine rev more; one answer was to fit aftermarket flywheel weights made by Competition Dynamics in the USA. The clutch was based on the T500 road bike with seven fibre drive plates and seven metal driven plates it was operated by a rack and pinion type mechanism. A five-speed gearbox provided transmission. Carburation was provided by a Mikuni 34mm carburettor featuring a fuel trap around the main jet, developed to keep the float level more constant by keeping the fuel in the trap area. Air filtration was by a large capacity, dry paper element housed in an airbox under the seat.
It had Suzuki’s Posi-Force oil injection rather than the usual pre-mix used on most competition bikes of the time, the two stroke oil tank was situated behind the right hand number plate. Kokusan Denki provided the sparks with their new pointless electronic ignition (PEI) that had an automatic spark advance curve from eight degrees at 2000 rpm to 28 degrees at 5000 rpm.
The front forks had seven inches of travel but this wasn’t all used because the standard springs were to heavy. Rear suspension also was very stiff and only provided four inches of travel.
It was very powerfull and unlike the ‘Works’ bikes of DeCosters it didn’t handle, infact it was totally different to the factory racers and more suited to the open type racing or desert races in the USA. For the more serious competitor specialist frame manufacturers produced frames to help the handling problems, Eric Cheney in the UK and Red Line Engineering in the USA were two such companies. Folding footrests were made from fabricated steel. The fuel tank had a steel twist type cap with air breather and badges that screwed on, the colour was Chrome Orange (Suzuki colour code 184) with a black stripe running under the badge horizontally.
TM400J (1972)
Virtually identical to the 1971 model apart from the colour which was now Philolina Yellow (Suzuki colour code 163) so it was more in keeping with the ‘works’ bikes.
TM400K (1973)
Again it was very much the same as the 1971 & 1972 models with odd changes. The air filter was now a more washable foam element. Footrests were now cast steel folding type. A different frame, forks, suspension units and swinging arm were all fitted in an aim to help the handling. The fuel tank had Suzuki stickers instead of badges and a blue/white stripe went round the back of the tank where the letters TM appeared.
TM400L (1974)
Much the same as the 1973 model, the L had straight type finning on the cylinder head and internally had been altered to reduce the compression ratio to a more useful 6.8:1. The front sprocket cover was now fitted with three holes for mud to escape from rather than the earlier type that had two diagonal slits. The exhaust system now had a rear silencer fitted to help muffle the noise. Suspension units were a newer type. The fuel tank now had dark green/white stipes that did a U round the rear of the tank.
Here is an advert for the TM range that was in Motorcycle Mechanics in January 1974. The photo in the bottom left hand corner shows Graham Beamish, the importer of Suzuki off road bikes at that time, outside his Brighton based company showroom.
TM250J (1972)
The new TM250J and was knicknamed the ‘CHAMPION’, After the RH71 ‘works’ 250 ridden by World Champion, Joel Robert. It was based very much on the TS250 trail bike and shared many engine parts including the figure of eight type Magneto cover and clutch operated through a worm and push rod arrangement. The sprocket cover was fitted with three diagonal slits and all the cases were finished in a satin matt black colour. The compression ratio was 7.5:1 and had a fan type cylinder head; the piston bore size was 70mm.
An exhaust system with no rear silencer certainly made the machine sound good and courtesy of a five-speed constant mesh gearbox it produced 30 bhp at 7,500 rpm. A 34mm Mikuni carburettor was fitted and foam air filter was boxed under the seat.
Ignition was by PEI (pointless electronic ignition). Suzuki’s own Posi-Force lubrication system was used with the two-stroke oil tank being fitted under the right hand side number plate.
Footrests were folding fabricated sheet steel type. The fuel tank was in yellow (Suzuki colour code 163, Aspen Yellow ! ), it had a black stripe following the outer shape of the tank and had Suzuki badges screwed on top of the stripe. The tank cap was a steel twist type with a breather pipe. The wheels had aluminium alloy rims with a 300x21 knobbly tyre on the front and a 400x18 fitted to the rear. The total weight of the bike was a very competitive 220lbs dry.
TM250K (1973)
Very similar to the ’72 model the K had the following changes. New type clutch cover with a rack and pinion type clutch operation, although the magneto and sprocket covers were still the same. The folding footrests were now the later type cast steel. Rear suspension units and swinging arm were the same as the predecessor. The fuel tank had Suzuki stickers instead of badges and a blue/white stripe went round the back of the tank where the letters TM appeared.
TM250L (1974)
Much the same as the ‘72/’73 models the L had these few differences. Straight type finning in the cylinder head. Smaller type magneto cover and a sprocket cover peppered with seven holes to clear mud easier.
A rear silencer was now fitted to the exhaust to lower the decibels. Front forks, suspension units and swinging arm were all uprated. The rear mudguard now bolted on to the rear frame loop. The fuel tank now had dark green/white stipes that did a U round the rear of the tank.
TM250M (1975)
Just a few changes over the previous models for the M model. The gearbox had some gears with different ratios. Suspension units were again different. The fuel tank was all yellow with the Suzuki logo written over a rising sun type design.
TM125K (1973)
The TM125K made its appearance in 1973 and was called the ‘CHALLENGER’. The engine for this lightweight and schoolboy scrambler’s favourite was based on the Suzuki TS125 trail bike, with many modifications. It produced 20 bhp at 10,000 rpm on open pipes or 18 bhp if the silencer was fitted. The colour is quoted in the parts book as Aspen Yellow (Suzuki colour code 163). The fuel tank had Suzuki stickers and a blue/white stripe went round the back of the tank where the letters TM appeared.
TM125L (1974)
Much the same as the ’73 models the L had these few differences. The fuel tank now had dark green/white stipes that did a U round the rear of the tank.
TM125M (1975)
Just a few changes over the previous models for the M model. New swinging arm and suspension units were fitted. The fuel tank was all yellow with the Suzuki logo written over a rising sun type design.
TM100L (1974)
With the schoolboy scramble scene really taking off Suzuki produced more small capacity machines for the 1974 season with the introduction of the TM100L Basically a TM125 with a smaller bore (50mm). The fuel tank had dark green/white stipes that did a U round the rear of the tank.
TM100M (1975)
Just a few changes over the previous models for the M model The fuel tank was all yellow with the Suzuki logo written over a rising sun type design.
TM75L (1974)
The TM75 was very much based on the Suzuki TS50, infact they both use the same frame. Mainly a schoolboy scrambler starter bike the TM75 is probably more famous as a pit bike for the road racing stars like Barry Sheene. It had a rotary disc induction with the carburettor on the right hand side of the engine. It had the Suzuki posi-force two stroke lubrication system with oil tank under the right hand number plate.
The clutch was operated by a worm mechanism on the left side engine cover and unlike the other TM’s it had point’s ignition. The engine hung off the frame and the front frame down tubes were just there for show. Footrests were rubber covered folding type off the TS100 and as a safety measure a chain guard was fitted above the swinging arm. It had a rod operated rear brake and its own ally forks. The fuel tank had dark green/white stipes that did a U round the rear of the tank.
TM75M (1975)
Just a few changes over the previous models for the M model The fuel tank was all yellow with the Suzuki logo written over a rising sun type design.
TM75A (1976)
Virtually the same as the ‘74/’75 models the TM75A model was the last TM made and had the following changes : The fuel tank had just the Suzuki name on it, the front number plate was now black and the side panels were yellow with black number plates stuck on. Front forks had been changed and the exhaust had a rear silencer on it to keep the noise down, as well as having a black coloured exhaust cover instead of the earlier chrome type.