carb swap

I read on another post that Wired George runs VM 26 carbs on his ST for mid range. I have both an ST and a kz650. Could I swap the carb banks on these bikes? this would give me the 28s on the bike I rip on and 26s on the bike I cruise on.

Thoughts?

KZ650 is 24mm. There is quite a bit of difference in the OD of both the inlet and outlets of a 24 vs a 26 or 28mm carb, somewhere around 3mm. You won't fit a 26 or 28mm on the KZ650 intake rubbers or the rubbers between the airbox and carbs without work and modification. Conversely though, putting 24mm on a KZ1000 is like a dream come true because everything slides right on because they are smaller than intended. I wouldn't recommend doing smaller than the 26mm on a KZ1000. KZ650 is OK with big carbs but like I said, not a 5 minute swap.

The KZ650 carbs are likely VM24; not VM26. The shaft carbs are VM28. They will fit; just swap carb holders from bike to bike... The 24s will actually be a good choice on the ST since it is ridden at mid-throttle most of the time where the smaller diameter carbs shine. I use VM26s on my 79 KZ1000E1 for that reason. We do test VM24 carbs on a KZ900 (903cc engine) all the time and they work fine... just won't develop all the power on top that larger carbs will.

So...If I switch the manifold (rubber to the head) from bike to bike, it should work? Will the rubber connectors from the air box to the carbs on the ST work with the smaller carbs? I run pods on the 650 so those should work.

Any ideas about jetting? The 650 currently runs a 17.5 pilot and a 115 main. The 1000st is a stock carb set up as far as I know because the whole bike is stock and I haven't been in the carbs yet.

The 650 VM24s are over jetted a tad on top... #110s would be about right for most applications with pods and aftermarket pipes. If I put them in the shafty, I would keep the #17.5 pilots (easier starting/idle) and use some #102.5 mains with the factory airbox... you could use #105 mains and probably not be way too rich.

With the 650, the stock 28 pumpers are a bit tricky to jet. First, you have to verify that the pump is working... take them off and with gas in them, work the pump to ensure all four nozzles squirt when you pull up on the pump arm. If it works, keep the #15 pilots, if it doesn't work, use #20 pilots. Since you will be using the pods on the 28s, you will need bigger mains. About #115 mains will be right with the pods. The jet needle isn't adjustable I think so don't worry about it.

Oh yeah... last thing, The bolt holes for the 24 carb holders will need to be elongated just a tad... I use a Dremel tool with cutter to open them up. The bolt spacing is about 1 to 2 millimeter more narrow on the smaller cylinder head.

Post edited by: wiredgeorge, at: 2007/07/10 15:32

Thanks for the advice. I tried the 110 jet first but it would not pull past 7 grand. The 115 pull cleanly all the way to redline. I think the previous owner did some mild porting to the head.

The pump on the 28s work. I did take the carbs off to replace all the rubber on the ST when I did the coils.

I look forward to doing this swap soon. Will I notice the difference in the 650 performance? I doubt I will notice much of a change on the ST because I strictly ride in the mid range on that touring rig.

It's a little more involved than just switching the intake manifold rubbers from bike to bike to swap the carbs. The bolt spacing is wider on the KZ1000 than the 650 and a very good chance several bolts are seized to the head and will snap off upon removal. Be careful and don't get too wild and crazy trying to remove the bolts or a mess will be the result.