78 KZ650 gearing for Touring/commuting

So I recently purchased my 78 KZ and love it. I bought it with the intention of using it as a touring/commuter. I ride 100 miles to work round trip. The stock rear sprocket is a 42 and the smallest aftermarket I can find is a 38. I just want to check and see if anyone has experience in this. Is it too much of a change? Will I still have decent acceleration? Also I was wondering about the front sprocket. I've heard you can only go up 1 or so teeth, but would it be worth it? Can I change both the front and back?

DaveKZR wrote:

So I recently purchased my 78 KZ and love it. I bought it with the intention of using it as a touring/commuter. I ride 100 miles to work round trip. The stock rear sprocket is a 42 and the smallest aftermarket I can find is a 38. I just want to check and see if anyone has experience in this. Is it too much of a change? Will I still have decent acceleration? Also I was wondering about the front sprocket. I've heard you can only go up 1 or so teeth, but would it be worth it? Can I change both the front and back?

WELCOME to KZR! We're glad you're here!

Would begin with a one tooth larger front (countershaft) sprocket, and leave the rear (drive) sprocket as is for the time being.

This is usually a simple easy swap, and makes a noticeable difference in lowered cruising top gear rpm, with about same attainable maximum speed and mpg. Also results in slower acceleration.

These engines are designed to spin, and they thrive on it.

Imo, good overall top gearing will barely pull redline.

Good Fortune!

So one tooth higher in the front will lower cruising rpm's but fuel consumption will remain the same? I am hoping to lower fuel consumption if possible?

I use this website when changing sprockets:
www.gearingcommander.com

upping the front sprocket will lower RPM's and fuel consumption (if properly jetted for that RPM range). However it will make starting out more difficult and lower the power you have in 5th. I did the front sprocket up a size and the back also and found the 100mph mark to be an elusive beast on my 650.

I'd step the front one and use the rear to fine tune it one tooth at a time.

What sprocket did you put on the back? I am most concerned with an efficient ride at about 70-75 mph. Thanks!

My 78 B2 runs good with a 17 front and 42 rear. Not too much clutching around town, and with the 120/90-18 rear tire she pulls an indicated 70 at 5 grand. I have noticed my gas mileage go down 2-3 mpg, not stay the same or go higher.