kz 650 top speed stock motor?

Don't know why I'm posting on a thread that some guy with 1 post started 4+ years ago.
But my 77 KZ650 custom brand new only ever got to 119 mph on the speedo , never could squeeze that last 1 mph out of her.

Got a lot of respect from my buddies on their 900's though, they couldn't shake me.

JD

650ed wrote: I've had my totally stock KZ650-C1 at an indicated 120 mph on numerous occasions. Any speedometer may have a little bit of error in it, but I have run side by side with a couple different Dodges, a GTO, and a KZ750 and their speedos read the same. Faffi grossly underestimates the speed at 110 mph, that would not be a decent running KZ650. Here is a link to an un biased Cycle World road test done back in the day. They recorded the speed at 119 mph. There are numerous other road tests that rear the same if you care to look them up. No typos. Ed


articles.kz650.info/documents/KZ650%20Cy...World%20Roadtest.pdf

I have the actual magazine and hence the test. The reason I'm sceptic about the listed top speed is that it did a 13.2 @ 98 mph whereas the KZ650SR tested a year later did a 13.4 @ 96 mph if memory serves, yet the latter topped out at 105 mph. And the KZ750 as well as the XJ750 both turned 12.4 @ 106 mph, yet topped out at 121 and 119 mph respectively. All tested by the same magazine. But the 119 mph of the original 650 could of course still be correct.

I don't have the article, but I have a few others and often the top speed was estimated, at least back then. The pdf looks to say "actual", though.

My 1982 KZ650 had badly pitted cylinder walls, poor compression, and used oil. It ran OK, but did not have much power. I never did a top speed run on flat ground. Recently, I replaced the cylinder block, sleeves and pistons from a 738cc motor. Running used but good piston rings and clean cylinder bores that still show the original cross hatching. Piston to bore clearance is .0013". Kept the 650 cylinder head, cams, etc., and used a standard thickness head gasket. Did some light porting of the heads. Am running stock exhaust, stock air box, and BS32 carbs, with one size larger main jets. My rear tire is one size over stock, or 140/90-16. The front countershaft sprocket is 14 tooth, whereas stock is 13. the rear sprocket is 33 teeth, which is stock. The bike runs considerably better than before.

I did a run yesterday on level ground with a light side wind. Since the 85 MPH speedometer is useless, I carried a GPS to record an true maximum speed. I weigh about 165. The effective gearing is higher than stock, (lower engine RPM for a given speed), due to the oversize rear tire, and the larger front sprocket. I tried running in 4th gear, but reached the redline, (9,500), and it would have gone more. Yikes! Shifted into 5th gear, and the bike topped out at 8,700 RPM.

Came back down to earth, stopped and read the GPS - Maximum speed was a true 117 MPH. Now I know this is a 738 cc motor, instead of 652, but it is far from perfect condition, and otherwise the engine IS a 650. I ran the numbers through "Gearing Commander" and it calculated that I would have been going 127.6 MPH. I know that is not correct. Perhaps the Primary Drive Ratio (2.550) I plugged in could be wrong, or maybe it gives speeds that are more like an actual speedometer might read. Anyway, I just thought this might be interesting data.

a little bit faster than a ninja 250

trianglelaguna wrote: a little bit faster than a ninja 250

Hahahaha

Those present day 250's are amazing

Have owned my 76 650 B1 since 1990. It is bone stock engine, sprockets, carbs, 4 into 2 original exhaust and has original airbox. Has under 20k miles. Wrung it out one morning in 2016. Believe it or not, got exactly the top speed as published in the cycle world magazine article, 119. Could not squeeze another mph out if it, was laying on the tank, tucked in to the max. Felt like the back of the bike was going to go airborne. Kids, don't try this at home....and don't let the gray hair fool ya!

.

bluej58 wrote: Don't know why I'm posting on a thread that some guy with 1 post started 4+ years ago. ...

At it again? Ha

I can't believe it's been 12 years. I kinda remember this post back in the day.

I read Ed's post about the bike having a foot of ground clearance, so I had to look it up in the gallery. It does have a pretty impressive ground clearance.
This is Dalley's bike (the original topic starter). Maybe those are KLR parts he used.

Digging up old threads can be fun.

The number I got on a 1979 KZ650B was just under 110 indicated... maybe 108?

But I actually think about this often, as a reminder of the really stupid things that young people do. My first bike was a '77 KZ650. About a year or two after I got mine, my best friend bought the '79 KZ650 from his cousin. He'd had it for a few days, done exactly zero to it ("Hey, it runs!"). I stop over and ask to take it for a ride. He lived on a rural road that was dead straight for almost a mile (but with driveways and cross streets). I hop on, fire it up, pull on his crappy helmet, and pull out. I run it down to the end of the road at a decent clip, turn around to head back, and just open it all the way up. Right up to terminal velocity, and stayed there long eough to be confident that it wasn't going to go any faster. I knew nothing at all about this bike, and I'd never even done that with my own bike (which I knew was well maintained). I didn't have any reason for doing that. Although the roads in that area, and that friend, were both associated with plent of very unsafe driving in cars. So maybe that's why it seemed like a normal thing to do. Anyway, I lived. And now I can say that a poorly maintained stock kZ650 will do nearly 110 mph.

Agree with the 119 top end ...... I've seen 9,200 to 9,300 in the red more than a few times and with a one tooth larger rear sprocket (41T) and a slightly taller rear tire and that should work out right there with a little tack error figured in. (Back to a stock 42 tooth now). Also have hit 9,500 to 9,700 with a 15 tooth front sprocket and the formula says that's about the same. With the bore, bigger cam and smooth bores I expect a few more but have backed off at 9,000 the few times I've try'd since due to a front tire that needs replacing (and maybe head bearings) and crappy roads around here. Hope it wasn't old age fear..... for sure not me being smarter.

A nice cool day with a 5 mph tail wind makes a huge diff too, along with tuckin in ....... and any kind of head wind and all bets are off.

Yup, there is definitely something that takes over the youthful brain. One of my earliest bikes was a Kz400 and I refused to let up until that damn needle touched 100. Luckily a slight tail breeze let me close the throttle after a minute or so.