Topic: CB750K Carb Identification

[oldbike]

Anyone know how to identify the type of Keihin Carb that is on these old 750's?  I am looking at buying a set of biigger idle jets.  How do I know if my bike has PE or PJ or CRS or however Keihin designates their carb models?

The reason I need to dig into this.  Bike has a set of .040 slow jets, runs lean at idle.  I found some 045, and it ran rich.   I need to buy some 042 jets.  I ordered them from a website based on the make and model of the bike (1974 CB750k4), and the jets are not the same as the ones I had in the bike (they are 32mm long, mine are 28mm long.)  Either the seller's info is wrong, or my bike had the wrong type of jets to begin with.  Need to find out what type of jets go in my carb.  Either Keihin jet N424-24 or N424-22.

Any help appreciated.

[bistromath]

Probably a stupid question, but have you played with the idle mixture screws?

[Simpson]

I would try to dial it in on the air screws first, if you are below 1/2 turn out then I would increase the jet sizes.
(I'm presuming the K0 and K4 are similar in adjustment)
My bike is running about a 43/44 slow jet that I hand drilled personally.
The main is #125.
Before increasing the sizes on the jets my air screws were around 1/4 turn and below.

[750goes]

the model of the carbs you are running - should be on the motor side, and is stamped on the top edge behind the choke arms - wipe them down with a bit of cloth and then get out the magnifying glass (thats what I need anyway)..
they should be PD44 or something like that...
let us know then will be able to tell what standards you should have inside them..

[oldbike]

stamped on the carbs in that location it says 657B ALI, and the A has a square around it.

thanks for the input on how to tune them, but really i need to know whether this carb should have the N424-24 or the N424-22 jet.  i am aware that the stock jet was .040 diameter, but since the bike has a questionable history, i need to know which MODEL jet.

thanks in advance for any help.

[oldbike]

i found this link:  http://www.motorcyclecarbs.com/Keihin_Jet_Identificaiton_Char_W56.cfm

they are saying that the stock jet is no longer available (99124-076) so you have to buy N424-24 jets and cut them to length!!  has anyone ever done this?  i think i might have jsut as much luck trying to bore my current jets oversize with a hand drill....

looks like i might be playing around with the needles some more. i hate to cut up jets except as a last resort.

anyone else been through this?