Need Oil/Air cooled GSXR advice

Hopefully there's someone here with a lot of experience with old Oil/Air cooled GSXR's...specifically a '91 GSXR750.

I'm having a lot of trouble getting the jetting sorted out...This is a 49 states bike with Mikuni BST38SS carbs.

The bike has the stock airbox and a Yosh Zyclone full system on it. I installed a Factory jet kit and 5 degree advancer and started at the baseline suggested setup that Factory provided. This was way too fat, especially up top. The way Factory said to do it was actually going down in MJ size, up in PJ size, different needle taper and up in "power jet" size.

I've got a combination now that's still a little fat throughout the range, but runs OK for the most part. The plugs are black and the exhaust is black. It wants to load up just a little sitting on the grid idling (maybe float adjustment) and it's a little soft on corner exits (maybe needle height) and it falls on it's face at 11,000 rpm so I have to short shift a little (stock power jet).

My question is this...has anyone set one up similar to this and do you still have notes as to what jetting/needle/float combination you ended up with?

 

OK...I tore into it today and here's what I found:

Needle clip on position #4 (way rich)

Pilot jet 32.5 (OK) this is stock

Main Jet 102.5 (way lean) Stock is 127.5

Floats #1 at 13.5 mm
#2 at 14.0 mm
#3 at 13.0 mm
#4 at 15.0 mm
(all set too rich)
Power jet #0 (blank) this is stock

Air screws at 2.5 to 3.0 turns (close to right)


Here's how I set it up for a starting point:

Needle clip in #2 position

Pilot jet 32.5 (stock)

Main jet 117.5

Power jet 62.5

Floats 16.5 mm

Air screws 3.25 turns


It really looks like the guy was fighting a really rich condition because of the float levels and tried to compensate by using the stock (blank) power jet and a much smaller main jet. Then when that leaned out too much on him he just set the needles full rich. I know that float adjustment is really critical on these things.

If anyone has any info that would help me fine tune this, I would appreciate it.

This was done by a guy that was at Roswell Fun Machines, but he is no longer there, so I can't really ask him what was going on.

 

It's been a while since I worked on one of those, but your jetting sounds pretty normal from what I remember. Riding the bike around will tell you if you've got the right needle clip position. Generally there's only one position that works worth a crap. In my experience, the old GSXR's made the best power when the porcelain of the plug was a golden/tan color. Ghost white is too lean (slower).

 

Cool...thanks Carl. I need to get a T and T day at Talladega or somewhere before VIR....

 

check your air filter..

I have a '92 750 that I check the settings on and see where they are at and let you know.

 

Joey,
That would be great...thanks.

These have got to be about the hardest carburetors in the history of mankind to get out and back in with the stock airbox in place.

I wonder if anyone has ever actually gone insane working on them? It's like the Japanese engineers are still trying to get even for WWII. "HaHa....Yankee have fun with this one....."