Honda MT125
Encyclopedia
The Honda MT125R was produced for the U.S. market in the years 1977–1978. It was a production Grand Prix motorcycle racing
roadracer designed for closed-course competition roadracing. The MT125R was produced by Honda Racing Service Center (RSC) and made available to the general public through the American Honda Motorcycle dealer network.
The picture shows how the MT125R would come out of the shipping crate. All white fiberglass
parts with only gelcoat
. The kit would also include a basic, but useful service manual and rear prop stand.
For many champion motorcycle roadracers, the road to the top started on a small engine capacity two-cycle motorcycle. Top roadracers like Randy Mamola
got their start on a 125 cc GP racer. Others like Ángel Nieto
spent their entire careers racing in the 50 cc, 80 cc and 125 cc classes.
Expansion chamber redesigned
Good examples of this model will have the original "RSC" tachometer
, factory prop stand which lifts at the footrests, owners/service manual.
A liquid-cooled kit was available from RSC which included: liquid-cooled cylinder, cylinder head, water pump, hoses, hardware, temperature gauge and radiator. This option is fairly rare.
The MT125R shares many parts with the CR125 engine. The CR versions were motocross bikes with similar specifications. One notable difference was the shift pattern on the transmission. Both had the standard 1 down 5 up pattern. On MT125R versions the shift lever was flipped over rearward to accommodate the rearset footpegs of the MT roadracer. To maintain the widely used 1 down 5 up pattern a different shift linkage was used behind the engine cover.
MT125Rs used a different cylinder than the CR versions when they were originally produced. At some point the part numbers were superseded by part numbers shared by both the MT125R and the CR125m Elsinore models.
Owners in search of parts after production stopped often substituted complete CR125M motors for their MT125R motors. The first clue is a reversed shift pattern from a stock MT125R (1 up 5 down).
Dyno test of Honda MT125 R-3
As with any 125 cc roadracer, it was best suited for smaller riders. After bump starting the engine a good start required patience and finesse. To characterize the personality of the 125 cc two-stroke look at the RSC factory tachometer. It did not move or display engine rpm until 5,000 rpm and registered up to 14,000 rpm. With the tall gearing needed for top speed performance it would not pull its own weight until the tachometer was showing at least 9,000 rpm. The engine was in its peak powerband or, "on the pipe" from just below 10,000 rpm and went out of the powerband a little past 11,000 (depending on jetting and modifications).
To achieve a good start the rider needed to hold the throttle wide open and begin feathering the clutch as fast as possible while keeping the rpm between 10,000 and 11,000 rpm. If the tachometer dropped below 10,000 RPMs the rider needed to pull the clutch in, rev the motor and begin the process again. If the clutch was engaged too quickly the engine could "bog" or even stall while the rest of the starting field rode away. Even with the lightest of riders, the MT125R required slipping the clutch for 40 or more feet. The rewards for a successful launch were full throttle with quick shifts (approximately every 1,000 rpm) up through the six gears. At the end of sixth gear the hard-working 123 cc engine would be pulling along a straight stretch between 110 and 120 mph.
Grand Prix motorcycle racing
Road Racing World Championship Grand Prix is the premier championship of motorcycle road racing currently divided into three distinct classes: 125cc, Moto2 and MotoGP. The 125cc class uses a two-stroke engine while Moto2 and MotoGP use four-stroke engines. In 2010 the 250cc two-stroke was replaced...
roadracer designed for closed-course competition roadracing. The MT125R was produced by Honda Racing Service Center (RSC) and made available to the general public through the American Honda Motorcycle dealer network.
The picture shows how the MT125R would come out of the shipping crate. All white fiberglass
Fiberglass
Glass fiber is a material consisting of numerous extremely fine fibers of glass.Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the invention of finer machine tooling...
parts with only gelcoat
Gelcoat
Gelcoat is a material used to provide a high-quality finish on the visible surface of a fibre-reinforced composite material. The most common gelcoats are based on epoxy or unsaturated polyester resin chemistry. Gelcoats are modified resins which are applied to moulds in the liquid state...
. The kit would also include a basic, but useful service manual and rear prop stand.
For many champion motorcycle roadracers, the road to the top started on a small engine capacity two-cycle motorcycle. Top roadracers like Randy Mamola
Randy Mamola
Randy Mamola born in San Jose, California is a former Grand Prix motorcycle road racer. He is considered one of the most talented riders never to have won a world championship.-Career:...
got their start on a 125 cc GP racer. Others like Ángel Nieto
Angel Nieto
Ángel Nieto Roldán born January 25, 1947 in Zamora, was a multi-time Grand Prix motorcycle roadracing World Champion. He is one of the most successful motorcycle racers of all time, with 13 Grand Prix World Championships to his name....
spent their entire careers racing in the 50 cc, 80 cc and 125 cc classes.
Features
- Engine - 123 cc 2-stroke air-cooled single-cylinder, 6-speed, power 26HP
- Chassis - fiberglass tank, fairing, fender and seat cowl
- Other - tachometer, mechanical front disk brake, and rear cable operated drum brake
Features
- Engine - 123 cc 2-stroke air-cooled single-cylinder, 6-speed, (1978 change), power 28 (1978 change)
Expansion chamber redesigned
- Chassis - fiberglass tank, fairing, fender and seat cowl
- Other - tachometer, (1978 change) - hydraulic front disk brake, rear cable operated drum brake
Overview
Good examples of this model will have the original "RSC" tachometer
Tachometer
A tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
, factory prop stand which lifts at the footrests, owners/service manual.
A liquid-cooled kit was available from RSC which included: liquid-cooled cylinder, cylinder head, water pump, hoses, hardware, temperature gauge and radiator. This option is fairly rare.
The MT125R shares many parts with the CR125 engine. The CR versions were motocross bikes with similar specifications. One notable difference was the shift pattern on the transmission. Both had the standard 1 down 5 up pattern. On MT125R versions the shift lever was flipped over rearward to accommodate the rearset footpegs of the MT roadracer. To maintain the widely used 1 down 5 up pattern a different shift linkage was used behind the engine cover.
MT125Rs used a different cylinder than the CR versions when they were originally produced. At some point the part numbers were superseded by part numbers shared by both the MT125R and the CR125m Elsinore models.
Owners in search of parts after production stopped often substituted complete CR125M motors for their MT125R motors. The first clue is a reversed shift pattern from a stock MT125R (1 up 5 down).
Performance and riding the MT125R
Dyno test of Honda MT125 R-3
| RPM | Standard HP |
Standard torque (lb/ft) |
Standard speed (6th gear) |
Modified speed (6th gear) |
Modified HP |
Modified torque (lb/ft) |
|---|---|---|---|---|---|---|
| 8500 | 16.67 | 10.3 | 88 | 88 | 14.16 | 8.75 |
| 9000 | 18.21 | 10.3 | 93 | 93 | 17.03 | 9.94 |
| 9500 | 19.9 | 11.0 | 98 | 98 | 19.54 | 10.80 |
| 10000 | 21.95 | 11.53 | 103 | 103 | 22.37 | 11.75 |
| 10500 | 24.39 | 12.20 | 108 | 108 | 25.01 | 12.51 |
| 11000 | 10.05 | 4.80 | 114 | 114 | 18.64 | 8.90 |
| 11250 | n/a | n/a | n/a | 116 | 17.07 | 6.57 |
| 11500 | n/a | n/a | n/a | 119 | 8.58 | 3.92 |
As with any 125 cc roadracer, it was best suited for smaller riders. After bump starting the engine a good start required patience and finesse. To characterize the personality of the 125 cc two-stroke look at the RSC factory tachometer. It did not move or display engine rpm until 5,000 rpm and registered up to 14,000 rpm. With the tall gearing needed for top speed performance it would not pull its own weight until the tachometer was showing at least 9,000 rpm. The engine was in its peak powerband or, "on the pipe" from just below 10,000 rpm and went out of the powerband a little past 11,000 (depending on jetting and modifications).
To achieve a good start the rider needed to hold the throttle wide open and begin feathering the clutch as fast as possible while keeping the rpm between 10,000 and 11,000 rpm. If the tachometer dropped below 10,000 RPMs the rider needed to pull the clutch in, rev the motor and begin the process again. If the clutch was engaged too quickly the engine could "bog" or even stall while the rest of the starting field rode away. Even with the lightest of riders, the MT125R required slipping the clutch for 40 or more feet. The rewards for a successful launch were full throttle with quick shifts (approximately every 1,000 rpm) up through the six gears. At the end of sixth gear the hard-working 123 cc engine would be pulling along a straight stretch between 110 and 120 mph.