This was an RS100 (itself a 1976 improvement upon the design of the original reed-valved 96cc RS100 that was introduced to the United Kingdom in September, 1974, and to the US in November, 1974)[1][2] with a front disc brake and a tachometer, and was replaced in 1983 with the square-stroke, 98cc RX-S (with part numbers coded 31J),[3] a major update on the RS design (with substantial changes particularly to the cylinder, head, and induction, and the points ignition replaced by Yamaha Capacitor Discharge Ignition) which was to form the basis of the Escort-distributed variants including the EY-100 Escort Yamaha 100.

The Escort variants of the RX-S had heavier gauge steel tubing and other changes specific to the Indian market, including slotted screws instead of the original Phillips.

Names of older variants of the RS line were re-used for Escort variants of the RX-S, including RX100 and RX-Z (a designation first used for a version of the first-generation RS100 updated with Capacitor Discharge Ignition) Following the poor sales of the Rajdoot 350, Yamaha needed to make a new product, and the recent success of Suzuki's AX 100 demonstrated the potential of small-capacity motorbikes in India.

In India in November 1985, Yamaha released the RX 100 (a variant of the RX-S, not the original RX100 or RS100DX) to widespread acclaim.

The RX 135 5 speed was later recognized as the quickest RX-series bike and has a continued cult status due to its rarity.

The final variant was a 4-speed RX 135 with a smaller catalytic converter silencer, classic rx100 like tank stripes and twin pod speedometer with white dials which was sold very briefly from 2003 to 2005.

The Japanese manufacturers responded in late 1997 with the Yamaha RX-135 and the RX-Z which had a tachometer and a sportier headlamp and body.

The final variant was a four-speed RX 135 with a small type catalytic converter, sporting a fuel gauge and a speedometer with white dials which was sold very briefly in 2003–2005.