What Jets Affect My Low Speed Running?

My '82 KZ650 CSR H2 has Mikuni BS-32 carburetors with completely stock jets, air box, filter, cams, exhausts, etc. The bike is cold natured - runs very lean - requires the first notch on the choke for the first several minutes even in the summer. Continues to be very lean but improves when warmed up. But even then, it feels lean. I realize that this is partly for emissions comtrol, fuel economy. etc.

Now anything over about half to full throttle is spectacular. I suppose this means that the main jets are about right. And the idle is very good, since the mixture is adjustable, and I have spent some time with this.

But the lean condition exists anywhere from just as the throttle is opened, up to about 1/3 throttle. It seems like there may even be some occasional misfiring until warmed up.

So what jets affect this portion of the carburetor's operation? I read about pilot jets, main jets, needle rods, but do not know which should be addressed. Also what size are these typically?

Will really appreciate the advice. Thanks.

Your old pilot jets may actually have a bit of crud (deposits) that make the amount of gas they flow a tad less than they should be flowing. The pilot jets are what effect idle mostly. The pilot jet type in your carburetors is BS30/96 and they are size #37.5. You can buy a new set of pilot jets and go one size up to #40. This will make warm up and starting easier. The drawback is, if you have any weakness in your ignition, such as in the spark, you may soot up plugs if you idle the bike a lot. Doesn't hurt to get a set of #40s and a set of #37.5s (stock size) and if the #40s cause plug fouling or sooting, then consider dropping the clean/new set of #37.5s in. You can get the pilot jets from www.z1enterprises.com or a variety of sources.

Thanks for the info. George.
The carbs are very very clean, since I have cleaned them about 5 times, before discovering a problem with a lack of venting, brought about by the previous owner's incorrectly routing some hoses.

What am I adjusting when I turn the external screws located on the top, front, left hand side of the carburetors? I thought these were the idle mixture adjustments. They typically run best when opened about two turns from closed.

Also, inside the carburetor, there are some tiny jets located in a protrusion not far from the main jet housing. I am guessing the diameter of these to be the .375 mm. The jet can be unscrewed. It is covered by a small plug about the size of a pencil eraser, with an O-ring on it? IS THIS THE PILOT JET ???

My education continues.

The screws in the front/center towards the engine side are pilot mixture screws and these control both air and fuel for the pilot circuit I believe. Turning the screw out increases the amount of fuel while the air going into the circuit remains a constant.

The wells adjacent to the main jet contain the pilot jet. On your carburetor the jet is a type BS30/96. The size is like #37.5. To access, you remove a metal plug with an oring. The purpose of the plug is to keep the pilot jet from drawing gas directly via the bottom of the well which goes down into the float bowl. There is a small hole crossing from the main jet well that supplies the pilot jet with fuel. On SOME versions of the BS34, there is no plug nor corresponding cross-passageway from the main jet well and the design of the carburetor is such that it is intended that the pilot jet should draw gas directly from the bowl. I believe the BS34s fitted to the 750 models have no plugs. The Suzuki BS32/34 models use a plug as well but use a rubber plug.

It isn't necessary for the plug to be especially tight in the hole but the seal of the oring must be good else the pilot jet will run rich. The plug itself is held in place by a pressure from the float bowl where there is a cast-in fitting in the bottom of the bowl which pushes on the plug to keep it secure and in place.

See Kawasaki.com parts diagrams for your model to get a better handle on the name of various parts and many times, the jetting is listed for many models.