1978 KZ1000 Top Speed

Can anyone tell me why my bike will not go over the 120mph mark. The bike runs fine up to 7000rpm and up to 120mph and then thats it. I have spokes front (19") and rear (18") and rear sprocket is a 33 tooth.I also have free flow breathers on the carbs, not the stock housing.I was also told it was good to run racing fuel once in a while in the bike to help it keep running better ? Comments on any of the above, thanks.

For a stock bike you are probably about where it's going to run....and it's acual speed is probably less knowing how "enthusiastic" KZ speedos are lol.

If it will not pull over 7000 I imagine you are running out of power. Keep in mind a 540lb motorcycle with 80hp is going to run out of steam before you do!!

Race fuel? Save your money.

Agree w/Terry on all counts... Few take into account wind resistance at speed..(it's real, & seemingly logrithmic) G

Will the bike run up to redline in 1st through 4th gear or does it bog at 7000 rpm in those gears as well? Ed

My 82 KZ dynos 125 mph before the rev limiter shuts her off.If ur doing an honest 120mph on an otherwise stock 78 KZ,I would get down on my knees tonite and thank the KZ gods for a wonderful bike amd leave well enough alone.bj

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pull redline in the first three gears...and as high as it will still pull after that...lay down and tuck your left hand into the dash......with a tail wind....you will hit 125....:laugh:

little gearing and some small mods and the kz will do 1130-140....the meat of the z is it's fun usable power in the rev zone of real world speeds rolling on outta corners and around traffic......like was said...you have a decent kz be thankful....

I rode my totally stock 650 pretty hard back in the day... I can remember one ride where I was at 9000 RPM at an indicated 190 KPH (118 MPH) for about an hour tailing a Porsche 911 on the highway.
That seemed to be topped out because I could rev it to the red line at 9500 but there was no more speed coming out of it.

Even if the speedo was off a bit it was still pretty fast riding... when you look down at the dashed line on the road and it looks solid, you have to be going at least over that 100 MPH mark.

Something is wrong if that motor won't rev to at least 9000... I ride my buddy's '76 1015 motor quite a bit and it revs past 9500 with no issues.

PS - not a good idea to look down at the road while riding...

thanks for the input guys ! 1st off,the bike as far as I can tell is bone stock except the kerker 4-into-1, the free flow air for the carbs. I am not a mechanic but love to ride this thing and the guy I took it to is a motorcycle mechanic that "claims" he used to work on these bikes new.

He said I needed the high octane to help the bike run better.

The speedo and tach look stock to me, so not sure if both are reading correctly or not, except I did go through a traffic radar "box" that let you know your speed and said I was doing 23 and the speedo was at 25. Might get worse the faster the bike goes?

I am glad I found this place with such a vast knowledge base and maybe I can learn to get the bike where it needs to be and KNOW it is right.

Thanks Again !

www.gearingcomander.com is the website I use when changing gear ratio's.

Mykuh wrote:

thanks for the input guys ! 1st off,the bike as far as I can tell is bone stock except the kerker 4-into-1, the free flow air for the carbs. I am not a mechanic but love to ride this thing and the guy I took it to is a motorcycle mechanic that "claims" he used to work on these bikes new.

He said I needed the high octane to help the bike run better.

The speedo and tach look stock to me, so not sure if both are reading correctly or not, except I did go through a traffic radar "box" that let you know your speed and said I was doing 23 and the speedo was at 25. Might get worse the faster the bike goes?

I am glad I found this place with such a vast knowledge base and maybe I can learn to get the bike where it needs to be and KNOW it is right.

Thanks Again !

just my .02, but that bike should easily rev to 9k....probably needs re-jetting......pods and a pipe require at least 2 up on the pilots and 3 on the mains if i remember correctly......then theres the baffle in the pipe...a lot of variables...if that thing wont pull cleanly to 9k, dont push it untill re-jetting...you are way lean and you will eventually grenade a piston....again, there are a lot of variables here....stock ignition/aftermarket, plugs good, carbs in a good state of tune, good battery,valves adjusted correctly, etc.......

keith1 wrote:

Mykuh wrote:

thanks for the input guys ! 1st off,the bike as far as I can tell is bone stock except the kerker 4-into-1, the free flow air for the carbs. I am not a mechanic but love to ride this thing and the guy I took it to is a motorcycle mechanic that "claims" he used to work on these bikes new.

He said I needed the high octane to help the bike run better.

The speedo and tach look stock to me, so not sure if both are reading correctly or not, except I did go through a traffic radar "box" that let you know your speed and said I was doing 23 and the speedo was at 25. Might get worse the faster the bike goes?

I am glad I found this place with such a vast knowledge base and maybe I can learn to get the bike where it needs to be and KNOW it is right.

Thanks Again !

just my .02, but that bike should easily rev to 9k....probably needs re-jetting......pods and a pipe require at least 2 up on the pilots and 3 on the mains if i remember correctly......then theres the baffle in the pipe...a lot of variables...if that thing wont pull cleanly to 9k, dont push it untill re-jetting...you are way lean and you will eventually grenade a piston....again, there are a lot of variables here....stock ignition/aftermarket, plugs good, carbs in a good state of tune, good battery,valves adjusted correctly, etc.......

I believe he's wanting it to rev to 9k in top gear, but many of these old bikes wont pull red line in top gear.