TOPIC:

I'm going through the carbs on the KZ900 I just picked up last week. Bike smells like it's running a little rich, checking the jets, it's got 107.5 in the mains and 17.5 in the pilots. Not sure off the top of my head but I think the stock jets are 115 and 20. Did any of the KZ900 come jetted this way? I'm just wondering why someone would go down on jet sizes. Bike has stock airbox and 4 into 2 pipes. I know it's hard to tell sometimes if a bike's running rich by smell alone. Here's a pic of #1 plug.

Stock jetting is 17,5/115 but you have to check the float bowl high, ignition Timing and valve clearance first.

Overall fueling is a stack up of all the jets combined.
So larger pilot can allow a smaller main.
Most Suzukis were set up that way which is why GS1000's only have 96 mains but 20 pilots.
This may be the case with yours and a smell of fuel only means there is a leak or flooding etc and cannot be determined as a sign of over richness.
The plug in the pic looks ok.

Checked bowls today, they were all over the place. I'll be going back to stock pipes from the 4 in 2s, am wondering if I should rejet it stock jets now or run it a little and see what the plugs look like. 107 seems way out. Someone told me some bikes were jetted like that from the factory, depended on what state they were going to. Still doesn't seem right... 8 under stock on mains.

Seems to me the best plan would be to get what you have properly dialed in before making more changes.
Get the fuel levels spot on.
Fine tune the low speed mixture.
Carefully synchronize the carbs.
Maybe stick in some new plugs.
Ride the thing, paying close attention to how it acts at various throttle openings and rpm.
There is a good tuning document running around this forum someplace. Basically, you first roll up to about 7,000 rpm then quickly go to full throttle. If acceleration is crisp and linear, the main jet size is ok. Then do the same thing from about 4,000 to check needle position. Finally from 1,500 or so to check the low speed (pilot) circuit.
Otherwise you could hook up a tailpipe sniffer that can record real time changes. A couple of guys here have hooked up a sniffer and posted results. Maybe Old Man Rock? Lou?

Unless you plan to run at high rpm's you don't need to worry about the main jet size at this point, but if you want some comfort maybe go back to stock size once you have the floats properly set. Mid range performance (from about 1/3 throttle to 3/4 throttle) is controlled by the needle jet (located above the main jet diffuser, extending into the venturi throat) and the jet needle that slides up and down in the needle jet. As you pull more throttle you are raising the jet needle and allowing more fuel into the venturi. The only time that the main jet controls fuel is when the jet needles are fully retracted.

Most people doing carb rebuilds will not change the needle jets or the jet needles. I would recommend it because they both wear from the constant flow of fuel through and past them. The best kits I've found are made by Keyster and are sold by Z1 Enterprises, among other distributers. They are expensive at about $36 per carb but you will get all the parts you need to do a proper rebuild.