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ive ridden a couple 650s they didnt feel very stable to me at high speeds.i think by the time you hack up a 650 frame and beef it up enough to put a 900-1000 motor in it you might as well start with a late 70s-early 80s 1000 frame,theyre a lot stiffer than the old Z1 frames everthing already fits you just need to remove extra brackets to lighten them up,you can gusset the 1000 frame also if you think it needs it.ive ridden the hell out of kz900-1000s with really big motors never dragged my knees but ive come awlfully close:evil: the only major twisting ive felt is in the stock swingarms on 77 and newer bikes.

you'll only really feel the flexing of these or any bike while encountering mid corner bumps, line changes, braking forces, ect. at the track level by at least an intemediately skilled rider who can easily grind the cases on both sides -- On these bikes, that's not exactly a hard thing to do, especially at a moderate lean angle in a LH corner. that being said, you have to have a tire capable of hooking up well enough to transmit the loads 'G's into the chassis to bring out the worst characteristics of flexing and these bikes in oem form didn't/don't really have rubber capable to do that. A purpose built track mule will have to wear 17" hoops to utilize modern rubber that will allow usable grip but it will also present the flexing issues of the forks, swinger, and frame under load that the bike was never designed for. modern radial race tires on 25+ yr old bike...yeah it's gonna flex big time! Most folks will only notice the swingarm flex riding the streets and that's if you have some nice 100+ mph sweepers in the area to get that Kz boat a wallowing and I hope you didn't just detail your tires with ArmorAll! but it looks really cool.

definately suffered the flexing swingarm syndrome on many a few occasions its not a good feeling on i-29 n in council bluffs taking that left ramp over to omaha at a 100plus! ive allways run metzeler me99s or comp k and they do stick unmercifully so i do get to know the limits of myself and my bikes on a regular basis,maybe ive learned to ignore the the frame twisting but i can definately tell you the stock swingarms really suck!

I would concur. I've run my 650 at the track a few times and with modern sticky bias-ply tires (GT501 and SuperVenoms) and it's really easy to get the pegs on the ground up until your cornering at 80+. At 80+ and severe lean angles the bike handles fine as long as your don't ask it go full left to full right (or vice versa). If your going from Left to upgright (accelerating onto a straightawy) it's not to bad. Going one side to the other can incite "wobbles" that'll make you tense up. tensing up of course only accentuates the wobbles.

Still I think the 650 is stiffer than my 900. And like most people I'm faster around the track on my 650 than my 900. It comes down to asking yourself if you really want to ride a 100+hp 30 year old tube frame bike at tire spinning speeds. I've come close to hi-siding a modern superbike, and don't even want to come close on one of these dinosaurs w/ bias ply tires. The 650 on the other hand you just wack open the throttle. No fuss, no muss. That confidence makes me quicker.

I also think the 650 would be a better candidate for a track mule, the dimensions favor it over the 900/1000 and the added torque the large displacement version I believe would be more of a hinderance trying to run one of these lumber wagons around a track especially the ones we have here in Phx. The handling and benefits of the smaller recip internals of the 650 should/would make it a faster track bike than the big boys. anyone got an old frame lying around??? gotta start somewhere. ever since Motorcyclist did that story on their vintage CB750 racer Big Benly I've had it in the back of my mind how fun it would be to build up a cool retro sbk for the track, something different, you see the occasional RD, but no KZ's.

I've got a '79 650 C3 frame with title. No forks and a bunch of other stuff missing.
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looks like the majority ha spoken. goodluck,happy wrenching!

You might want to talk to Steve Darlington a fellow kzr member. He has a ton of experience racing his kz middleweights in the vintage classes. He is very knowledgeable and knows how to build a class winner. I don't remember his username to send him a message but he has some cylinder heads for sale listed in the kzr classified area. You might be able to track him down there and pick his brain. He is a good guy to deal with.
Cheer-Colin Firth -Ontario Canada

Post edited by: reborn650, at: 2006/02/04 17:55

i've got a 77 kz1000 frame i could part with.

arobsum:before you hack up that frame send me pm,im kind of partial to 77-78 kz frames

attention passengers.....hijack in progress. lol

and i would of gotten away with it too,if hadnt been for those meddeling kids(MKII)bwaha!