TECHNICAL DIFFERENCES.

Apart from colorings and name RZ/RD between all models sold in the world are:

Speed limit warning light ( at 80 km/h !!) and red zone in speedometer for japanese bikes for '80 to '84 and after '84 warning light in RPM meter
   
Seat with rectangle inprints for '80 to'82 RZ250/350 and square rear mirrors for all Japanese models
 
Catalysed model for USA with the following specificities: dual two stage catalytic converters inside the mufflers with thermic sensors, heat shield on pipes, a reed-valve to admitting filtered air to each pipe and warning light & buzzer alarm for pipes temperature. On Californian models, a third catalytic element in the headpipes complete the system and a carbon cannister is added for venting of the gas tank and carbs. See all details on this page
 
Carburettors with the 2 throttles commanded by 2 linkages connected to a pulley (and 2 push and pull cables: push to close and pull to open the throttle) for USA models and some Japanese models ("desmodromique" system). The cover of the carbs are not screw but held on by 3 screws. The two carbs are bolted together with two brackets. They have non adjustable jet needles, and only the geniune needle jet is available in order to owners don't adjust carbs setting for the good works of catalyst system to respectect the pollution level authorized by the EPA (Environmental Protection Agency) like we can see on the against sticker on the bike. Fuel tank filler have a restricted diameter to only accept unleaded size nozzles.

Smaller licence plate bracket for USA & Canada due to smaller licence plate. Following picture for bracket from '83 models
 
Lateral reflector for USA, Australia  & Canada.
   
 
Different Carb setting and/or restricted Exhaust (Parts of metal are welded in the exhaust down pipes reducing the internal diameter from 33 to 26mm) for 50 & 27 HP for '85 model & '86 1WW & 1WX German models 50HP for insurance classes and 27HP for "1A" license
 
352cm3 displacement + different Carb setting + restricted Exhaust with "catalyst" part metal  working with unleaded fuel only + longer rear mudguard (rear fender) for 1WU Swiss model to be OK with noise emission law. This model is restricted @ 45HP (33.3 kW). Fuel tank filler have a restricted diameter to only accept unleaded size nozzles
 

Partial fairing and not perforated brake disks , '83 cylinders (31K model) with carburettors without power-jets like '83 one & specific cylinder head wich do a compression ration of 5:1 for '86 & '87 Brazilian model.

Grease nipples on the suspension links.

Specific handle bars and switches.

 
Fuel tap without diaphragm unit, ie fuel is gravity-fed through the tap (wich include a filter), rims partially painted and gold brake calipers on '87 Italian 2UA model made in Brazil and on brazilian models
 
Electrical switch on lateral stand (if you forget the stand, the engine stop when you put a gear) on '86 to '91 models for UK, Germany, Denmark, Sweden, Finland, Austria & '84 to '85 USA models
   
 
Fairing with twin head-lamp , remote-operated choke on left-hand lower panel fairing & exhaust with silencers removable with '83 31K cylinders , carburettors without power-jets like '83 31K & specific cylinder head wich do a compression ration of 5:1 for '91 to '93 Brazilian model
 
Fairing with twin head-lamp , remote-operated choke on left-hand lower panel fairing & restricted exhaust with different carb setting (extract from HAYNES manual), greaser on bottom suspension arm et suspension legs for '92 to '95 English, Italian & Spanish 4CE model (Made In Brazil)