GT750A Carburettor Type

[johnbennettgt750j]

I'm trying to improve the way my GT750A runs and I have some detailed questions regarding carbs. I have two sets of carbs which i believe are the Mikuni variable venturi BS40 type. There are one or two detailed differences between the carb sets. So my first question is where do I find the carb model/part numbers? Are they stamped on the carb bodies because I cant find any identification on either set? Are there more than one model/part number carb of the BS40 type? Were the carbs fitted to the L,M,A and B models the same?
The main difference between the two sets of carbs I've got is that the throttle valves in one set are #110 and the other are #120. The parts book I've got is dated 1974 and is for the L model and this shows the throttle valve should be #120. The bike seems to run better with the #120 set fitted but cosmetically the other set looks best. Can i swap the #120 throttle valves to the better looking carb set or are there two types of carb body one to suit each type of throttle valve?
Also my Haynes manual says the pilot jet size for L models is #47.5 and for M and A models its #45. Both my sets of carbs have the #47.5 pilots fitted. No direspect to Haynes but I would like confirmation on this.
Please advise what is the correct/best carb model, pilot jet size and throttle valve for a 1976 GT750A?
Any help and information and experience will be gratefully accepted.
The bike starts easily and runs well through the mid range and top end with either set of carbs fitted. I'm sure many people would be happy with this but I'm pretty fussy and it doesn't want to idle properly especially with the #110 set of carbs fitted!
With the carbs removed I can see that with the #110 set with the throttle closed, the pilot mixture outlet holes are covered by the throttle valves!
Thanks in advance for your assistance.

[Alan H]

Speak to Baz on here. He restores carbs and I have had several sets for my 550s & 750.

More info here - https://www.oldjapanesebikes.com/GT750_ ... ide/page-4 and https://www.pinkpossum.com/GT750/carb/BS40carbs.htm

[Rijko]

120 is L specific
https://www.oldjapanesebikes.com/GT750_ ... de/page-81

So unless you have L cylinders or an L engine, the bike should run best with the 110 set.

L specific :

The throttle slide cut away is a 120, which changed to 110 in 1975
Pilot jet is a 47.5 which changed to a 45 in 1975
Spark plug was a B6ES, which changed to a B8ES in 1975
Ignition timing is 3.64mm BTC for the R and L and 3.42mm for the centre which changes to 3.62mm for the R and L and 3.42mm for the centre
Air screw setting is 1/4 turn open, changing to 3/4 turns open in 1975
The stock choke lever actuator originally had a rubber cover seen to the lower left - the replacement unit on the lower right lacked this if you lost one, although the part number (13413-31210) didn't change