Carb/airbox setup '88 GSXR 750 w/older motor

[RogerRZ]

Hey all, I'm Roger, from Canada. Have been biking for 36 of my 42 years, and recently joined the say what now!? ranks. I've been wanting a Slingshot ever since they came out in '88, and finally got one.

My screen name, comes from my Yamaha days when I had various Yammies, but notably a stock, and really ratty RZ500, and after that, a breathed on RZ350, in Team Marlboro colours. I presently own a Kawasaki Concours, and a clean '76 CB400F. But I digress.

 I recently bought a decent '88 750, and all the parts are there, but they're not all correct, it's a mish-mash of different years' components.

It has an R705 motor, so it's from an 86 or 87, but it has a bank of 36mm Slingshot carbs, with stock jetting (112.5 MJ, 37.5 pilot). Pilot screw is out three turns, but I'm still having trouble with the idle. It's slow to idle down to 1000 or so, if I turn it down, it stalls, if I turn it up, it goes to 2500-ish--the tach starts at 3k, so I'm guessing. It also has mufflers (not sure about the headers) off an 1100, of unknown vintage. My CB400F had the same issue, and was fixed by going to a different pilot jet.

I had the carbs out to issue a clogged pilot jet (results were positive), and getting the airbox boots was a pain in the dink. 

My question is, let's say I wanted to go with K&N duals, and jet kit, (if nothing else to make carb servicing easier) is the fact the motor is an older 749cc going to affect my choice of jet kit? Do I need a jet kit? Do the 1100 mufflers flow more? Does it matter?


I will also be looking at changing the CDI, as I don't think the old motor will like the short stroke 13.5k limiter, and also the sprockets--I didn't take the front cover off, but the rear is a 47 tooth, and the bike is revving 6k at 60mph in top.

Thoughts?