The starting serial number for the 1973 engines is 'GT750-31357', and the 1973 models transitioned the location of the engine serial numbers, moving from the right side of the upper engine case underneath the right carburettor to the left side of the upper crankcase half above the drive sprocket at frame 36198.
The K series engine changes included:
The water bypass line area mating surface between the crankcase halves was increased, and an o-ring was added to ensure a better seal at frame 36198.
The SRIS valves were converted to a threaded fitting and strainers were added at engine GT750-31343. These strainers originally were plastic, but product failure occurred with extended use. As per service bulletin GT-18, the strainers were changed to a more durable all-metal design at engine number GT750-39084
An adapter kit was made available to re-route the SRIS line to the left cylinder and which connected to a modified spigot mount offered for both the J and later K models. This was changed to a fitting in the barrel casting mid 1973.
The clutch uses a sleeve bearing and resin clutch plates - later models used a needle roller bearing and alloy plates beginning with engine 57533
The alternator and points covers no longer had the name 'Suzuki' cast into it, but rather now had a recess to take a stamped aluminium adhesive backed label. This aluminum sheet adhesive label had a black background with a gold trim surround and neutral coloured lettering which was embossed. The stamped steel ignition cover that previously had Suzuki with a surround stamped into it was also changed to having a recess to take the same aluminium label as was used on the updated alternator cover.
The original crankshaft design used a non-flanged oil seal on the right inboard oil seal (next to the drive gear) - these should all have been changed over under warranty repair to the new oil seal style having a flange to prevent the seal from moving, or more probably just had a 'c-clip' installed to achieve the same thing to avoid having to disassemble the crankshaft. This is detailed in Suzuki service bulletin GT-6, and the changes were factory installed starting at engine 49895.
The carburettors were the same AMAL style model of Mikuni VM32SC as used on the model J, but differed from the 1972 carburettors as they used a high top cap as per the photo to the right and also had longer slides and springs.
The carburettors were mounted to the cylinder block with rubber adapters held in place with clamps, as per the photo to the right, although early model year K's did use the bolt on spigot mount shared
with the 1972 J model.. The later rubber adapters were specific to 1973 as the spigots on the engine side of the carburettors were a smaller outside diameter than the Mikuni BS style used in 1974
and later models.
As mentioned in the previous section, the original crankshaft design also included fully floating small ends on the connecting rods, with fixed big ends - in fact the crankshaft, connecting rods, and pistons are quite different from the later models starting late 1973 and onwards. This table to the right shows the changes in parts numbers.
As previously offered, the kick starter was not labelled on the right side engine cover, nor was the gear shift pattern cast into the left side drive sprocket cover. Also worth noting is that the oil
filler cap for the transmission oil is threaded in the 1972 and 1973 model years, and then changes over to a push fit (the original part number is 09259-20003 changing to 09259-19001 for the 1975 model year)
The radiator ends still had plastic side covers as used in 1972, but now they were chromed. Also - if you look at them closely, you will notice that they have taller stand-off's to add a small amount
of additional clearance from the radiator, possibly to minimise the cracking you often see at the tops of the radiator end covers on the 1972 J model.
The cooling fan was still fitted as standard equipment.
There was no grill covering the front of the radiator (although one was offered as an optional extra, and after market and dealer installed grills were common), and the radiator crash bar was common to both the 1972 and 1973 models having two bump bars extending vertically located at about the 1/5 and 4/5ths position.
The shift rod extending the width of the crankcase was shorter in the 1972 and 1973 builds than in later model years, and as a result the shift lever for both 1972 and 1973 has a pronounced sharper bend outwards than do later models. The rubber protector on the shift lever is a capped tube, rather than just an open ended sleeve, and there is a Suzuki 'S' in the end.
The water pump impeller was keyed to the shaft up till frame 37158, after which a rolled pin was used.
The oil pump used in the 1972/1973 models had three plungers, rather than two as was used from 1974 onwards. For an excellent overview on GT750 oil pumps, see Richard's explanation on his Pink Possum web site , which is also available in the Appendices section of this site.
At least some 'K' models had red coloured oil lines - as yet it is unclear whether this was due to Suzuki having several suppiers, or due to an actual design change.
The kick start lever is fairly straight when compared to the post-1973 models, and the rubber cover had a Suzuki 'S embossed in the middle on one side.
The exhaust system had black conical tips on the ends, and cross over coupler pipes (ETCS) connecting the three downpipes together at the front.
The retainer flanges were the smaller finned units (14182-31001) introduced just prior to the 'K' model release. A third retainer flange having slightly smaller fins and a 'rounder' look was introduced in 1974. In the lower photo to the right, the early J style is on the left, the later J/K style is in the middle and the style used from the L onwards is on the right side.
