The body is semi-self-supporting with frame and engine with automatic gearbox in the rear part.

Type B 731 (as well as whole 700 series) underwent during its long production many changes and modifications.

Among the most significant belonged replacing of the noisy rear axles Rába with another that has not produced so much noise, change of the engine mounting and change the location of alternator, use of several types of engines LIAZ, initially aspirated, turbocharged later.

In newer buses have also been used automatic gearbox Voith (apparently from 1991) instead of the product of Praga.

Began to be mounted exhaust gas catalysators EKOS and between 1993 and 1994, the buses were equipped with intercooler and intake air (due to meet emission standards Euro1), which also led to modifications of the body – behind the third door was placed the intake grille.