Deciding what sprockets to use

'79 KZ650 B3

Broke the chain the other day. Front sprocket looks OK, rear not so much. Doesn't make sense to me to replace the chain and the rear sprocket, but not the front; it'll only cost 20 bucks or more.

Besides, I want to lower the gear ratio, anyway. This bikes primary purpose is to save gas, I'm not overly concerned with losing a little performance to get better mileage.

The manual says it came with 16/42 (front/rear) stock. That's a ratio of 2.63:1

My bike has 16/41 for a ratio of 2.56:1, so someone has already made some changes. It's still pulling 4800 rpm at 60 mph, though, and I want to cut that by at least 500 rpm.

I read this thread with a lot of interest: kzrider.com/component/option,com_joomlab...w/id,174468/catid,5/

He has a 630 chain, and went from 13/33 (2.54:1) to 13/26 (2.00:1) That cut his 60mph rpms by 1050 rpm, but, he admits to having to slip the clutch quite a bit on takeoff.

I think 2.00:1 might be a little extreme for me. i figure I can get my 60mph rpms down the 500 rpms I want by getting somewhere in the 2.20:1-2.30:1 range.

I looked on Z1Enterprises.com. Here are their choices for 530 chains:

Front:

16 tooth

17 tooth

18 tooth

Rear:

40 tooth

42 tooth

So, here are my choices:

16/40 gives me 2.50:1. Too stiff

17/40 gives me 2.35:1. Close, but not quite there

18/40 gives me 2.22:1. Perfect.

The problem is, I've read about people having problems with clearance on 18 tooth front sprockets. The page for the 18 tooth sprocket on Z1Enterprises.com says it fits my bike, but, after what I've read on here, I'm feeling cautious.

17/38 gives me 2.24:1, and would avoid any clearance issues. The problem is in finding that 38 tooth rear sprocket.

Has anyone run an 18 tooth front sprocket on a KZ650? Which way would be better?

I've been running a 17/41 combination on mine. Works out well. The 18 toothed front, if it fits won't leave much clearance at the little guard in front of the sprocket at all.
I just recently won a NOS 38 tooth rear sprocket on Ebay, and got a new 17 front and chain. For the cost I always replace all three together, not much sense in putting a new chain on worn sprockets or vice-versa.
I haven't tried it out yet, maybe someday this cold and snow will stop in the northeast so I can try it out,, .
Since I did my carb conversion I have a lot more low end torgue so hopefully I wont' have to slip the clutch to get it going.. Time will tell.

what carb conversion did you do?

It has been discussed on here a few times. I converted to a single carb. Do a search for stromberg if interested or PM me.
Ride safe

Check out Z1Enterprises for a 38 tooth rear sprocket for a 750 twin (stock size). I am fairly sure the 750 twin front and rear sprockets will fit on the 650's.

I use either 17/38 or 17/37 sprockets on the 750 twins and think that ratio works real well.

I "think" the 18 tooth will fit if you remove
the metal guard in front of the sprocket,
but I haven't tried it so I'm not sure.

Post edited by: steell, at: 2008/02/09 16:22

The sprockets for the KZ750 twins are identical to the KZ650 sprockets except for one thing.

The KZ650 sprocket has a 74mm center.

The KZ750 twin sprocket has an 80mm center.

That would leave the sprocket completely bolt-centric. I'm not sure how I feel about that, I can see where it could be problematic.

Well, I found the correct 38 tooth rear sprocket, but I'm a little leery of buying from Spacely Sprockets.

Don't worry, George Jetson say's there good sprockets! :woohoo:

Good to see there's at least one other old fart on here

One? I'll bet 50% or more of the guys here are 50+. I'm 54 and totally a kid at heart!

Bluemeanie wrote:

I'm 54 and totally a kid at heart!

Especially since they came out with those dingie pills