77/79(?) KZ650 B/C(?) pump carb jetting

A friend and I got to talking a couple weekends ago about a barn he just inherited from his father. Apparently, while poking around it for the first time that Satuday morning, he came across what looked to him to be an old KZ650 and he wanted to know if I was interested in any parts from it.

Naturally, I had to see it. It was indeed a KZ650. The frame and registration states it's a 77 KZ650C. The engine, however, has a 650B stamp on it.

Moving the kick slowly, it turns fully and smoothly. No hangups, no odd sounds. Overall, it's rough with some notable rust but looks practically complete and stock with 15K on the odometer. The only obvious issue is that one of the carbs is missing and the other three are in pieces on a bench (hence while it was probably stuck in the barn...another death due to an uncompleted project?)

Wanting to try to get her running, I'm looking at a set of carbs said to be from a 79 KZ650LTD. They have an accelerator pump and I assume they're VM24SS.


With the exception of the engine stamp, everything else appears stock so I'm guessing that jetting should be 102.5 and 17.5. Does that sound right? Should I stay away from the accelerator pump carbs and go for more year specific carbs without the pump and in that case, what would the jetting be in this case (not sure if the B/C model makes a difference)

Should I try to detirmine what year engine it is?

Post edited by: Virii, at: 2007/07/16 12:17

Chances are it's the original engine. There were no KZ650C engines. All KZ650C motorcycles had a KZ650B serial number engine from the factory.

Wow, you're right! I just went out and checked mine...Can't believe I never noticed that........

The jetting you noted for the VM24 pump carbs isn't correct... check www.kawasaki.com , owner info, parts diagrams and look up the year/model for the carburetor parts diagram. Kaw never installed #17.5 pilot jets on any of the VM24 series. I don't think it will have a #102.5 main either.

Beautiful, thank you! I've been poking around all morning and find sizes listed on various forums that are all over the board.

I never looked at my pilots so can't confirm, but they list #15 as stock. 102.5 was the main jet size at least on 1977-78 models.

In 79 quite a number of assemblies were used with a variety of main jets... some were as small as #90 and #97.5 was also used. I don't think they used a #102.5 in 79 but it doesn't hurt to use that as a starting point as the smallest main jets are too small to pull redline...

Yeah, I had wondered. Looking at the parts diagram, it does show 15's for the pilots but I'm uncertain how to detirmine the stock main jet from the information provided.

As you mentioned, it lists main jets ranging at 90, 92.5, 97.5, 100, 102.5, 105, up to 107.5. I was leaning towards assuming that perhaps around 100 might be a good starting place and I'd go from there. It sounds like that'll at least get me close.

I've never played with carbs that had an accelerator pump, would I normally want to go smaller on the pilot jets on those than I would in carbs that didn't have an accelerator pump?

Thanks for your help!

Post edited by: Virii, at: 2007/07/17 09:55

I have pretty much given up trying to match the main jets to their respective assemblies. Some of the sizes are listed as "racing" and were never installed at the factory. Go with the #102.5 size for a stock airbox. The smaller sized main jets don't flow enough gas, even for a stock airbox. Use #15 pilot jets for pump models... it is easy to get way too rich if the pump is working as it should. The pump itself takes a lot of fiddling to get them working right in most cases. You can test by filling the bowls and moving the pump arm up... give it a few pumps because if the carbs have been sitting, the pump needs primed. You should see gas squirt out of all four brass fittings in the middle of the venturi.

Most of the time, when I service these carbs, the brass fittings are clogged. The main problem with the pumps; other than the pump diaphragms being old and not working is that gas is picked up in the bottom of the #2 carb. Unfortunately, this pickup place is in a well and hard to get to and there is a check valve on the other side of the pickup hole. This check valve is generally clogged. It is hard to clear. If you can't get the pump working as it should, the carbs will need to be rejetted totally different. I often toss the pump bowls and close up the openings for the nozzles in the venturis and rejet 28s for this reason. The 28s respond well after being rejetted and work a whole lot better than 28s with pumps and are, of course, simpler and less prone to problems with the pump gone.

Good to know, thank you for all your help! It's greatly appreciated!