Whats the difference

What is the difference between a k750 an a kz750 of 1981 or is there none?

I have not heard of a K750, do you mean a Z750? Also, in 81, both the two and four cylinder 750s were available.

yes meant the Z750 was there a difference in them

My understanding is the KZ's were sold in the U.S. and the Z's in Europe.

Maybe this will help/confuse you:

Kawasaki Model Designations

SHOWROOM NAMES MODEL DESIGINATION

250 LTD (SINGLE) Z250C

Z250T (SCORPION) ER250B (BELT DRIVE)

GPX250 EX250F

ZZR250 EX250H

KLR250 KL250D

KR250 (TANDEM TWIN) KR250A

KR250 KR250B

KRIS KR250C

250 ELIMINATOR EL250E

GPZ305 EX305A (CHAIN) EX305B (BELT)

GPZ400 1982 ZX400C

ZXR400 ZX400H (IMPORT) ZXR400L

440 LTD Z440A (CHAIN) Z440D (BELT)

GPZ500S EX500A AND THEN EX500D

ER5 ER500A 2001 MODEL ER250C

GPZ550 1981 Z550D1 1982 Z550H 1983 ZX550A

GT550 Z550G

550 ZEPHYR ZR550B

550 LTD Z550C

GPZ600R ZX600A

GPX600R ZX600C

600 ELIMINATOR ZL600A (US IMPORT) ZL600B UK

KLR600 KL600A (KICKSTART) KL600B (ELECTRIC START)

ZZR600 ZX600D AND THEN ZX600E

ZX6R ZX600F 95-97 ZX600G 98-99 ZX600J 00-01

KLR650 KL650A

KLR650 TENGAI KL650B

KLX650 KLX650C

650 CUSTOM Z650C

650 SR Z650D

650 CSR Z650H

750 LTD TWIN 1977-1979 Z750G 1981 Z750Y1

750 LTD TWIN CSR Z750S1 (US IMPORT)

GT750 Z750P

750 LTD (FOUR) Z750H

GPZ750 (TWIN SHOCK) 1981 Z750R1

GPZ750 UNITRACK ZX750A

GPZ750 TURBO ZX750E

GPZ750R (WATER COOLED) ZX750G

750 VULCAN VN750A

750 ZEPHYR ZR750C

ZR7 ZR750F

ZXR750 ZX750H 89-90 ZX750J 91-92 ZX750L 93-94

ZX7R ZX750P

ZX7RR ZX750K 91 ZX750M 93 ZX750N 96

900 LTD 1976 KZ900B

GPZ900R ZX900A

900 ELIMINATOR ZL900A

ZX9R ZX900B 94-97 ZX900C 98-99 ZX900E 00-01

Z1000 LTD 1015cc 1977-1980 KZ1000B

Z1000 CSR KZ1000M

Z1000 LTD 998cc KZ1000K

Z1000 ST Z1000E

Z1000 MK11 Z1000A3/A4

Z1000 CLASSIC EFI KZ1000G

Z1000 EFI Z1000H

Z1000 LAWSON Z1000R (THE REAL REPLICA WAS A S-MODEL)

GPZ1000RX ZX1000A

GTR1000 ZG1000A

ZX10 ZX1000B

1000 ELIMINATOR ZL1000A

GPZ1100 (TWIN SHOCK) 1981 Z1100B1 1982 Z1100B2

Z1100 LAWSON Z1100R

GPZ1100 UNITRACK ZX1100A

ZZR1100 ZX1100C AND THEN ZX1100D

GPZ1100 WATER COOLED ZX1100E (ABS) ZX1100D

1100 ZEPHYR ZR1100A MAG WHEELS/ ZR1100B SPOKE WHEELS

ZRX1100 ZR1100C WITH FAIRING ZR1100D W/OUT FAIRING

ZX12R ZX1200A

Z1300 DFI ZG1300A

Z1300 VOYAGER ZN1300A

Yeah Mfolks pretty much has it pegged...my take is that the term 'KZ' had negative connotations in Europe (it was a designation for WWII era Nazi concentration camps...google 'KZ' and see what you get). So, Z models came out in Europe and Asia while KZ models were released in North America.