650 vs 750 cams

my 77 650 is a stock motor minus the vance and hines pipe, dyna ingintion, pod filters and vm26mm carbs. i am thinking of installing 750 cams to boost the bottom line a little. would i really notice a difference in this? over the winter i would like to install the 810 kit in her and was wondering if they would work well or should i go aftermarket for it. or would i be better off going the 700 kit with 750 cams? i have the cylinders for a 750 and the price is close for either the 700 or 810 kit. i dont know what direction to go. also,would my 26's be ok for either combo or should i start looking for 28's or 29 smoothies? nothing to make a barnburner or somthing like that,i just want to move at a little better clip.thanks in advance!

Hey Steve. With my old '77Kz650 Custom, I did both of the big-bore engine projects you are considering.

Last year I put a Wiseco 700 kit into the 650 cylinders, with stock rejetted Mikuni 24's, ported 650 head, cams, pipe and filters. The bike ran pretty good, way better than stock. Part of this performance increase off the line might have been the 14 tooth drive sprocket which makes a big difference for acceleration, but takes away from the top speed. I am more about hammering it through the gears than high speed highway blasts.

For the 2006 riding season I decided to go with a bigger plant with a bit more scoot under the saddle, so over the winter I picked up 750 jugs and head from an '80 750/4. After researching on the Kzr archives and speaking with some other 650/750 racers I decided on the following set-up

810 Wiseco for the bored 750 jugs. I was convinced to stick with the 650 head because of the small combustion chamber. I ported and polished the 650 head which was milled 10 thou.

I put in Kz750 cams, Gpz springs, 750 intake valves, Dyna coils and ignition, Custom tuned Wired George Mikuni 28's, MAc pipe, 14 tooth sprocket. I went with velocity stacks instead of pod filters for the retro look. They give a way-too-cool throaty roar that comes outta these chrome trumpets when I crack the throttle wide open. I don't drive in the rain or on dirt roads so the skimpy filters on the stacks are sufficient. This bike was built for short little blasts in the city usually late in the evening when there is less traffic on the road.

I kept the stock '77's Hy-Vo chain, pulleys, adjusters and cam chain sprockets, switching them onto the Kz 750 cams. The only modifications I had to make to the 650 block were to open up the bottom end engine cases/bores to handle the 750 jugs. I also had to put in a different bolt from the front and rear of the 650 head to connet to the 750 jugs-neither of these mods were a big deal.

This old girl with the 810 combo is a screamer and will spin way past 11K on the tach while still pulling. It would take a pretty well tuned '70's litre-sized bike to outrun me up to 60 miles per hour. Maybe the driver has some input on the impressive performance:)

This package has worked very, very well for me.

If you have any questions send me a message.

Cheers-Colin Firth-Ontario Canada
1977 Kz650 Custom, 14,900 miles bought new by my brother in 1977. Miss July 2006 Kzrider Calendar. Two different paint schemes, stock Moon Dust Silver and Custom Inferno Red with Silver and Gold Stripes. Superbike bars, bead blasted rims, engine, sculpted seat to hold me in when I crank it open .

2007 Toyota FJ Cruiser
2006 Chevrolet Uplander
Restored, 1974 Kawasaki KS 125 Enduro with 7200 miles.

thank you very much! that answered almost all my questions. now i'm kinda leaning on the 810 side.the only thing i forgot to ask is what jetting would you recomend for this setup and are you running a baffel or wide open? (by the way, love your avatar! i saved it to a screensaver)

The MAC pipe is stock except for adding an extra screw to keep the baffle in for street use.

Cheers-Colin Firth

reborn650 wrote:

...I kept the stock '77's Hy-Vo chain, pulleys, adjusters and cam chain sprockets..

Colin, probably a typo, but the pre-81 650s don´t have a Hy-Vo (multiplate) cam chain, but a single roller chain - first 650 to use a Hy-Vo cam chain like the 750 fours is the F2. Just to avoid confusion.

Steve, before spending a lot of money on parts, make sure your 750 block has the recesses for the cam chain idler gear shafts on top of the block like the 750 block pictured below. There seems to have been a transition period where the 750 fours used 650 blocks with 750 sleeves installed - these blocks will work with pre-81 650 cam chains. A standard 750 block meant for Hy-Vo cam chain won´t have these recesses (they use plastic sliders instead of cam chain sprockets) so you can´t install the cam chain idler gear shafts.



Post edited by: OnkelB, at: 2006/09/05 10:34

OnkelB wrote:

reborn650 wrote:

...I kept the stock '77's Hy-Vo chain, pulleys, adjusters and cam chain sprockets..

Colin, probably a typo, but the pre-81 650s don´t have a Hy-Vo (multiplate) cam chain, but a single roller chain - first 650 to use a Hy-Vo cam chain like the 750 fours is the F2. Just to avoid confusion.

Steve, before spending a lot of money on parts, make sure your 750 block has the recesses for the cam chain idler gear shafts on top of the block like the 750 block pictured below. There seems to have been a transition period where the 750 fours used 650 blocks with 750 sleeves installed - these blocks will work with pre-81 650 cam chains. A standard 750 block meant for Hy-Vo cam chain won´t have these recesses (they use plastic sliders instead of cam chain sprockets) so you can´t install the cam chain idler gear shafts.

Onkelb is correct. My bike had the roller chain not the Hy-Vo. I stuck with the roller. He is also correct on making sure you use the correct block with the recesses. The block I used was from the early 750'4 and aside from the cylinder head to block bolts and opening up the 650 cases there were no major issues.

Another thing to consider is that if you go with the hotter, higher rpm/power Gpz cams you will have to go with an electronic tach as the Gpz cams do not have the tach drive gear.

Cheers-Colin Firth-Ontario Canada

<br><br>Post edited by: OnkelB, at: 2006/09/05 10:34

Post edited by: reborn650, at: 2006/09/05 23:06

Post edited by: reborn650, at: 2006/09/05 23:06

Onkelb is correct. My bike had the roller chain not the Hy-Vo. I stuck with the roller. He is also correct on making sure you use the correct block with the recesses. The block I used was from the early 750'4 and aside from the cylinder head to block bolts and opening up the 650 cases there were no major issues.

Another thing to consider is that if you go with the hotter, higher rpm/power Gpz cams you will have to go with an electronic tach as the Gpz cams do not have the tach drive gear.

Cheers-Colin Firth-Ontario Canada