AHRMA Vintage Superbike Middleweight Racer

Saving Another One From the Compacter - It’s Ok, Everything’s Going To Be All Right Now

So the donor bike finally made it home today. I have seen many bikes in worse shape, but many more in better.

It has been several years now that this 1979 Kawasaki Kz650-C3 which was manufactured in 10/1978 was left in the elements with nothing but a measly tarp to keep it from rotting … and as you will see it didn’t work.

The first job will be to assess everything. Many of the pitted and rusted items (rear fender, exhaust, shocks, etc) will be removed and tossed/donated to others with projects where they will be useful. The rear seat rest/luggage rack will be spared the garbage heap to either be sold or configured to work on my 1976 Kz900-A4 for touring purposes (I would only want the luggage rack, but the wife would be very happy with the back rest).

I am still trying to formulate the budget/plan for the project and most of it will be dependent on what we find in the engine when I start tearing into it. I am a little concerned that the #2 cylinder has a good amount of rust in it. The engine turned slightly and then lodged when I picked it up. I was able to remove all spark plugs except the one for #2. I have it soaking in penetrating oil right now and plan on removing the exhaust to spray the inside of the cylinder, so maybe things will work out (doubtful).

For those who aren’t aware, I don’t really have the option to overbore the Kz650 for the AHRMA Vintage Superbike Middleweight class as anything more than +1mm would put me out of spec. Unfortunately there are no +1mm kits available through normal channels anymore for the Kz650 either. We’ll see how it goes. New rings may be another challenge…as I believe they are quite expensive/rare right now.

Anyways – here are the unblemished/raw photos of the poor girl now that she’s home.

More pics of the Kz650 as she looks today. Not sure why, but the only fender I care about (front fender) is in excellent shape. Go figure...

The plan, as it stands right now is the following:

2013 Participation in AHRMA Vintage Superbike Middleweight

• Freshen/blueprint engine – tear down to the cases and replace/document all components
• Rebuild front forks with progressive springs and fork emulators
• Replace rear shocks and springs with progressives
• Remove rear fender, rear tail light, blinkers, headlight (leave shell)
• Replace controls and handlebars
• Rewire electrics, install DynaS ignition found in a donor Kz750 motor
• Simple port/polish for head, valve job (if necessary, likely is)
• Deck head
• New rings
• Install Mikuni VM26 or VM28 carbs from Z1/Kz900/early Kz1000 (non-accelerater pump model preferably)
• Racing tires
• Frame / Swing arm bracing
• Rear sets
• Paint / Decals

All of this is to be completed before late Summer of 2012 so that I can participate in a track day class.

In case you wonder - this would be my first attempt at racing. This is a new thing for me, a new bike, and a lot to learn. Can't wait to dig in! :woohoo:

This should be a fun project. You know I'm watching.

is this for raceing or track days ? or both?
should be a fun project.

.

mark1122 wrote: is this for raceing or track days ? or both?
should be a fun project.

Both. The overall intention is to start a long term racer project with a lower initial cost to participate in the AHRMA races. There are three in the area I can reasonably attend (1 at Road America and 2 in Michigan) and long term I'd love to try to get to more of them.

Here's the organizations Vintage Road Racing page: dev.ahrma.org/?page_id=43

Thanks for the encouragement. I won't have any progress at all until next week sometime since I'll be traveling for the holiday. Progress will be slow as I don't have a huge budget.

Long term there are any number of engine performance modifications I would like to make - I'm trying to keep the cost down and just get on track initially focusing more on improving the chassis and suspension (what's there, not swapping anything at this point) than engine hop-up. I do want it to be reliable, though.

Research, research, and more research.
Hunting for the magic formula…

As my budget is not infinite (…of course…) nor exactly “large” I am trying to plan out the best route to get the motorcycle ready for racing. Since the bike already has a fairly large displacement for the class it will be run in I am going to try to focus mostly on suspension and engine reliability.

The Kz650 was known for fairly good reliability when it was introduced so from the engine standpoint we will mostly be going over it’s condition and getting it into good running order. I plan to measure wear/clearances on all components, install stronger studs (since I’m in there anyways) and new fasteners all around. The only other modifications I plan to make initially include decking the head to slightly increase compression and swapping the semi-problematic automatic cam chain tensioner for an APE manual cam chain tensioner.

Not having raced before, and not understanding a lot about motorcycle geometry, I have been doing as much reading as I can regarding spring rates, dampening, and geometry. I have found a couple of spring rate calculators online, both of which give slightly different results and neither of which matches up with available rear suspension spring rates.

For example:

SonicSprings.com ( www.sonicsprings.com/catalog/calculate_s...g_rate.php#calculate ) shows that I should get a 1.1 kg/mm rated spring.

RaceTech.com ( racetech.com/ProductSearch/2/Kawasaki/KZ650/1977-80 ) shows a 0.998 kg/mm rated front fork spring rate and asks to call for a rear shock fitment.

According to Google, the spring rates convert as follows:

0.998 (kg / mm) = 55.8854198 pounds / in

1.1 (kg / mm) = 61.5971561 pounds / in

While this is all well and good for the front suspension (RaceTech.com has new springs and fork emulators I plan to use for the front suspension) this gets really confusing when we start looking at the rear suspension. The spring rates I have found for a set of replacement shocks for the Kz650 (admittedly not racing oriented as my budget will not allow for those currently) are listed as 90/130 lbs/in (dual rate) or 1.61/2.32 kg/mm ( www.progressivesuspension.com/pdfs/7100-105.pdf ). And these are the lowest of the spring rates available for these replacement shocks.

I have also come across the following page and am trying to digest it as well: ( www.peterverdone.com/archive/springs.htm )

I'd be very interested in spring rate/dampener feedback from others who are racing (TurboGuzzi, CoreyClough, and others... ). I believe to some extent this will vary based on the track, but a good ballpark to start with it more or less what I'm looking for.

there is a whole lot of learning to be done here bud. suspension can get pretty deep.
I have only just begun to scratch the serface.
the easiest way to start to figure out the springs and damping is to call racetech. tell them your bike and plan. they will give u advice from proven knowledge. those of us on low budgets cant afford to do everything by trial and error.
i would recommend, not putting money into shocks and forks that are inefficient for your task.
do some research to find out what forks and shocks the racers are using, and follow there lead. Racetech may be able to help here.
for example: Arther (dbsuperbiker) choose forks from an'86 ZX10, gutted of the antidive and re-valved. They are stiffer than the orig forks...no more high speed wobble, but require extensive tuning to suit each track and keep the front end from chattering under high cornering speeds.
find the ones that the most guys like for a kz650. maybe sv50 forks ?
then put your money into them, so u know u have the best for your budget, and u wont have to redo them later.
U wont be changing the forks or shocks valuing, for each track as a beginner.
It wouldn’t hurt to run stock for a year to learn how it feels stock. The biggest draw back with old fork technology is that they dive badly when u brake hard. If they bottom out, which is quite possible, u can have an oh shit moment, as this sudden jolt transfers to the tire ,and traction is upset. This causes clearance issues in the corners too, as the suspension compresses under turning loads u ground out. So u have to go slower.
the biggest limiting factor that I find running modern rims on my kz is the lack of clearance.

Do u have a local track that u can run track days on ? How about a race school class that u can use your own bike ?

mark1122 wrote: i would recommend, not putting money into shocks and forks that are inefficient for your task.

Thanks, makes sense. I figured the cost of new springs (at a minimum) to stiffen the front end was worth it - it's not a huge cost, and I expect my "play" money to increase a year or two into this.

U wont be changing the forks or shocks valuing, for each track as a beginner.

Yeah As little as I know I would do more damage than good...

It wouldn’t hurt to run stock for a year to learn how it feels stock. The biggest draw back with old fork technology is that they dive badly when u brake hard. If they bottom out, which is quite possible, u can have an oh shit moment, as this sudden jolt transfers to the tire ,and traction is upset. This causes clearance issues in the corners too, as the suspension compresses under turning loads u ground out. So u have to go slower.

How about stiffer springs - is it worth it? RaceTech's replacement springs are reasonable (in my eyes) and I am willing to spend the money on them. Even the emulators aren't that expensive, although I see your point - I could have a used front end for the same cost, but I would have to put out more to get it fitted/working. And I think I'd have problems with tires as the front end would have the newer/wider 17" rims and I'd be stuck with the stocker rim on the rear.

Do u have a local track that u can run track days on ? How about a race school class that u can use your own bike ?

Yes, and yes. Both are in the plan before I start racing in 2013.

But I have to get the bike put together first - it's not ride-able right now. And I'm pretty sure the rear shocks are completely gone so I was planning on "freshening" both ends. All together new fork springs, emulators, and rear shocks from Z1E with progressive springs were right around $550 plus some shipping. I don't think I could have a used/upgraded front and rear suspension for the same, but I haven't really looked into it. I'm also limited in using a tubular steel swing arm (or as Arthur stated an authentic period piece, and I'm not about to find a CalFab swingarm and matching wheel/rear brake for cheap).

Feedback is welcome! Thanks for all input!

DoubleDub wrote:

mark1122 wrote:

How about stiffer springs - is it worth it? RaceTech's replacement springs are reasonable (in my eyes) and I am willing to spend the money on them. Even the emulators aren't that expensive, although I see your point - I could have a used front end for the same cost, but I would have to put out more to get it fitted/working. And I think I'd have problems with tires as the front end would have the newer/wider 17" rims and I'd be stuck with the stocker rim on the rear.

** Talk to racetech. Get there advice. Springs are only about $120. and they can tell u how much space to start with. The spacer acts like a preload . so it raises the bike up. But it will still dive bad. I think springs would be a must do.
But find out what the best fork brake combo is. Find the cost. Weigh your options and have a goal to work towards.
Most parts u buy aftermarket, can be resold later without a big loss.

Do u have a local track that u can run track days on ? How about a race school class that u can use your own bike ?

Yes, and yes. Both are in the plan before I start racing in 2013.

** why wait till 2013? Do u have another bike u can use next year. Or just get the 650 going stock. If u can, Just do track days to get your feet wet . don’t worry about raceing, just get seat time.

I'm also limited in using a tubular steel swing arm (or as Arthur stated an authentic period piece, and I'm not about to find a CalFab swingarm and matching wheel/rear brake for cheap).

Feedback is welcome! Thanks for all input!

** when the time comes for an upgrade. Talk to Leon. He can add a brace to your current arm..

My post didnt turn out as pretty as yours. u are obviously more puter savvey than I. lol