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Discussion Starter #1
I have a '78 KZ650, and at 60mph I'm running about 4500 rpms, maybe just a little lower - is that good?

Also, it seems like there's a pretty big powerband for each gear, or maybe I'm just shifting too soon - in 5th, it feels like there should be another gear there, but obviously there's not - is this normal?

Thanks;

-John
 

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Lots of ways to look at it. The engine is probably redlined at 10k rpm? So, the bike would be running over 120mph at 10k if it had the hp to run that fast. These engines can handle the rpm. If it was geared higher, it wouldn't have as much acceleration in top gear. My ZN700 is indicating 5k rpm at an indicated 75mph, probably less than 70mph actually. Redline is 10k. For cruising on the interstate, the engine sounds busy, but it can take it. I suppose you have the option of changing sprockets to lower the rpm. My ZN700 is shaft drive so I don't really have that option.
 

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Discussion Starter #3
So, the short answer is Yes, it's fine...? I get plenty of pickup in 5th if I roll on the throttle; I've had it up to 75 in 5th, and it feels like there's way more to go... I just don't want to 'overstress' the engine in the lower gears by cranking it way up before I shift.


Redline is at 9K(indicated), btw...
 

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Yes, it's fine. The Japanese 4cylinder engines are capable of running those high rpm. If you do a lot of touring you may want a bike a little more designed for that but you can tour on your bike if you want. I remember reading about the Florida to Alaska ride on the Voyager forum that a couple guys did. One guy rode a 250cc Suzuki and his buddy rode a 600cc Honda scooter with a trailer in tow. So, you can tour on anything you want.
 

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Your bike is chain driven via sprockets. The rpm at a given speed is derived from the number of teeth on those sprockets. If the bike feels buzzy at 60 mph, do some research and buy new sprockets which will effectively lower the rpms although this will also decrease acceleration a tad but make highway droning a bit more comfortable.
 

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The KZ650 is kind of high revving & can be more so depending upon what model you have if it still has the stock sprockets. You can change gears at almost any rpm within reason, just so long as you stay out of the red line & don't lug the engine by shifting way too early which is kind of hard to do on a 650. I think the 70s redline is at 9k. The 81-83 KZ650 redline is 9.5k.

First thing to do is to verify what sprockets & drive chain you have. number of teeth for each sprocket & 530 or 630 drive chain. Then you could search your bike in the JT Sprockets on-line catalog to see what other sizes are available. There should be a pretty wide range of choices. Z1Enterprises dot comes has JT sprockets.

I'm running the stock sprockets on my 81 KZ650-CSR >> 13T Fr & 33T Rr w 630 drive chain. 33/13 = 2.54 which seems kind of high revving to me when I'm in 5th gear. I plan on switching to a 530 chain & sprockets when the time comes to get new sprockets, and also lower the ratio a tad. If I kept the 630 stuff, the lowest I'd go is a 32T Rr. The next size down was the 30T Rr, but I think that ratio would be too low with a 13T Fr & the size is NLA anyway.

For comparison some of the 70s 650s have a 16T Fr sprocket & 42T Rr w 530 drive chain. 42/16 = 2.625, so this would feel even more high revving to me than my stock setup.
....
 

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As mentioned previously, you can change the gearing to suit your needs within reason.

Most modern bikes run 530 chains which are 5/10 of an inch rather than 6/10 so each link is shorter. This allows smaller sprockets for the same number of teeth and hives a wider range of options.

I fitted a 530 chain to my GPz750 and an offset front sprocket from a GSX1100 when I put the ZXR400 rear end on.

I calculated the standard gear ratio and searched for front and rear sprockets to give me as close a match as possible then measured the distance between the centres of the wheel spindle and gearbox shaft to determine how many links I’d need on the chain.

It’s all pretty straightforward maths really although I had the added complication of a different size wheel (17” from 18”) and tyre profile to add in to the equation.

The top speed of the Z650 was around 115-120mph so half way yo the red line at 60mph sounds about right.
 
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