Help! Confused about sprocket specs on 1980 KZ750

Hello All,
I am confused concerning sprocket specs on my 1980 KZ750 Ltd Twin. I have seen factory specs at both 16/38 and 13/32. I have 13/32 on mine, and am wondering if I can increase front to 16. Have read other threads indicating that a 14 front may not even fit. I can currently running 5000 rpm at 60 mph. Want to get to 4000 rpm at 60 mph. Or am I just dreaming?

Thanks!

Try here for help in figuring ratio's. It also includes tire sizes for chain speeds. www.gearingcommander.com

Not sure, but a larger 630 front sprocket may not physically fit; a 530 might work - don't know. I don't know much about ratios n stuff, but a 16/32 seems like it might lug the engine when moving the bike in first gear. Again, without knowing much & using a calculator to figure the ratios, a 30-tooth rear sprocket might be good.

Edit: My mistake - I missed the part about the bike being a twin. The above in in reference to the 750-4 Ltd.

I run 530 chain on my 750 twin, stock gears are 16/38. You can go up to 17T on the front and still fit, not 18. 32T on the rear is minimum and the chain heads do rub on the aluminum sprocket holder (wheel hub).

I ran 16/32 and was VERY happy for many years. I weighed about 160, so the bike didn't have a big load to pull. I also am not into drag racing, so less acceleration doesn't bother me. It cruised much smoother.

I recently had to replace sprockets and chain and went to a 17/38 and I don't like it at all. I would think about 17/36 or 17/35 would be my optimal gearing with a 110/90-18 rear tire.

YMMV

JMKZHI wrote:

Not sure, but a larger 630 front sprocket may not physically fit; a 530 might work - don't know. I don't know much about ratios n stuff, but a 16/32 seems like it might lug the engine when moving the bike in first gear. Again, without knowing much & using a calculator to figure the ratios, a 30-tooth rear sprocket might be good.

Won't fit with 530 chain. Don't know about 630.

cacker wrote:

I can currently running 5000 rpm at 60 mph. Want to get to 4000 rpm at 60 mph. Or am I just dreaming?

Thanks!

When mine was stock (16/38 with 530 chain) it spun 5k @ 70 mph which is about 4300 @ 60 mph. When I went to a 32 rear, the 70 mph RPM dropped to about 4200 and it would cruise fine at that speed. 60 mph RPM was about 3600, and it cruised very well there.

Thanks for the feedback. I am running the stock 130/90/16 rear tire with a 100/90/19 front. I don't know what size chain is on, 530 or 630. I am a big guy, 250 lbs, I am not concerned with how fast I get to 60, just want to stay there without my hands and feet going numb from the vibs.

I also have a plexifairing windshield and notice substantial drag into a good wind.

So, I guess I want to be sure that I have enough power transfer with the new sprockets to get to 60 or 70. I suppose I could always drop to 4th in the wind.

Also, what kind of fuel mileage do you guys see with the 750 twin, I am hard pressed to get 30 mpg.

Thanks again.
Chip

cacker wrote:

Thanks for the feedback. I am running the stock 130/90/16 rear tire with a 100/90/19 front. I don't know what size chain is on, 530 or 630. I am a big guy, 250 lbs, I am not concerned with how fast I get to 60, just want to stay there without my hands and feet going numb from the vibs.

I also have a plexifairing windshield and notice substantial drag into a good wind.

So, I guess I want to be sure that I have enough power transfer with the new sprockets to get to 60 or 70. I suppose I could always drop to 4th in the wind.

Also, what kind of fuel mileage do you guys see with the 750 twin, I am hard pressed to get 30 mpg.

Thanks again.
Chip

I average about 40 mpg in city only, about 55 - 60 mpg on highway (for 60 mph average) and about 48 mpg at 70 - 75 mph average.

Cacker:
With 13/32 gearing, I am almost positive that you have a 630 chain. Measure one of the links. A 630 will be 3/4". A 530 will be 5/8". The first numeral in the chain spec. is the number of 8ths of an inch for the chain pitch.

I have been all through this gearing thing with my 650. I went to a 26 tooth rear sprocket, with 13 tooth front. It rolls away from a stop sign easily enough, but not at all suitable for drag racing. Hell the bike will do about 55 MPH in first gear. Has a 130/90-16 rear tire.

What I have found, is that the bike does well up to about 75 MPH. Excellent gas mileage (50 - 60 depending on speed. The windshield definitely increases drag - big time. Above those speeds, or with a strong head wind, you are laboring the engine quite a bit. 4th gear performs better and still matches MPG with 5th at this speed.

A 16 tooth front sprocket with a 630 chain WILL NOT fit on the front. I tried it. Still have the sprocket.

All things considered, I would recommend a 14 tooth front and a 30 tooth rear sprocket. I believe your chain length will still be good for this.

Send a PM if you have more questions. I am a "gearhead" through and through.

WABBMW wrote:

...A 16 tooth front sprocket with a 630 chain WILL NOT fit on the front. I tried it. ...

Bill, his bike is a Twin, so what doesn't work on your 650-CSR may work on his 750-2.

I have ordered a 15t front and 32t back sprocket and new 630 chain. Will let you know how it rides. Thanks for the help.

I'll bet you will love that gear ratio.

If you have 32/13 now, your new gears will drop your RPM by about 13% compared to what you are running now.