There are a couple of prerequisites that you need in order to make
any real performance increases on air cooled engines.
The first is an engine oil cooler. See the oil cooler section.
The second is the ignition system. A typical points and condenser
tune up kit costs $40. An electronic ignition such as the Dyna S cost ~$100.
It will pay for itself in 3 years, and requires no maintenance.
Once you install it you are done. You will never have to pull
that side cover off again except to lube the advance mechanism.
The addition of coils and wires will permit you to open up the
spark plug gap to ~0.039. This will increase top end engine performance,
give better starting characteristics, and extend spark plug life.
The third is to know what you want. The level of performance you want
to reach will determine the extent of mods required.
The entry level of performance increase is a 4-1 header and carb re-jetting.
This will get you at most 10% more than you already have. You have to get a
true performance header for this. If you want the most out of it you will need
to pull the baffle. For a Z1 or KZ1000 you can get ~92 HP max. The addition of
a good drop-in aftermarket cam will improve performance greatly and may get you
to the 100Hp mark depending on the state of the engine tune.
The next level involves expensive items. To get more power you need to up the
compression of the motor, that means pistons. Figure on $500 for pistons and to
bore it out. The max displacement you end up with depends on the motor you start with.
A 900 Kaw will go to 1015cc, a 1000 Kaw will go to 1075cc, an 1100 Kaw will go to 1170cc,
and a GS1100 motor will go to 1168cc. Note here that you are looking at the 120-130HP range
for 1075-1200cc motors. The third level involves carbs and cams. Here are the next big
expenditures, Mikuni RS carbs, figure $500-600, depending on size. Figure 34 or 36mm carbs
for the street. Cams all cost ~$275. You will have to deal with what you end up with.
Unless you are going to spend a lot of time at the drag strip, stay away from cams
with more than 260 degrees duration @0.050 lift. Any more than that is unstreetable.
You will have to get aftermarket springs and guides for this. I strongly recommend
porting, see the head porting part of this series, and replacing all valve guides.
A performance valve job is a must. Depending on the cam lift, you will need to
clearance cut for the cam lobes. 0.400" and more will require this.
Now we are up to the 130-150HP range.
The fourth level requires re-sleeving the cylinder block for big bore pistons.
There are many additional mods that add costs here. The sleeves, machining the
upper case, crankshaft welding, and boring the cylinder block are additional
costs added to pistons and bore and hone. Figure $160 for sleeves, $85 to
install them, $59 to bore the upper case, and $59 to weld your crankshaft.
Finally, we are looking at the 140-180HP range. Let me draw a big line here.
This is the point at which you leave the street and enter the track. Typically
some items are borderline and others are blatant problems. If you go past the
fourth level you need a professional drag racer to guide you through your
expenditures. The final level means ultra high costs. Big blocks allow
displacements up to 1500cc and cost just under $1k. When you hit this level
you will need transmission and crank mods. Here you can spend more, much more.
Big blocks also tend to give short ring life on the inner cylinders due to the
temperature problem inherent with these units. This is where I leave it. I do
not recommend big blocks for the street. They burn up, overheat, and cost too much.
But, if you have special street requirements such as serious cash money racing,
there is no other way to go. There is no replacement for displacement. The bigger
they are, the faster they go. That's a 1260cc WISECO big block in a '82 KZ1000J
shown in the pics. That is a 9-second motor in street clothes.
One thing you need to think about is how you want to go about your project.
Planning will go a long way in reducing frustration for the 1st or 2nd timer.
As a guide start slow. You do not have to do everything at once.
Try this order of mods.
1- electronic ignition
2- Dyna or Accel coils and wires, gap spark plugs to 0.037-0.042
3- Individual K&N air filters and header with baffle installed. Increase the main
jet size to 10-15 higher than OEM as a start. Do not mess with the needle.
On bikes with exhaust air suction valves just remove the valve and all tubes.
Put a piece of hose between the 2 nipples on the valve covers,
4- For all round performance go with a 15 tooth front sprocket and a 39-tooth rear.
Put a new chain on, 94-96-98 links will work for most applications. If you want a
more drag racing setup, go with a 41-42 tooth rear sprocket.
5- replace fork springs and rear shocks with progressive suspension units,
6- replace the steering stem ball bearings with tapered roller bearing units,
7- repack and inspect all wheel bearings, replace as needed,
8- oil cooler - lengthen engine life and performance,
9- Install a good drop in cam, Web Cam grind #118 and Cam Motion grind Z2,
these will get you almost a second in the Œ mile compared with the stock cam,
This gets you as much as you can get without making internal engine mods.
This may also bring to light out any problems that were hidden in your motor
by the low state of tune it was in. Worn out valve seals and rings are common problems.
Now for the fun part; internal engine mods. This is where the performance
comes from. The bigger the motor; the faster the bike. An excellent choice
for a project engine depends on what you have to start with. If you have a
1015cc Kaw, go with a 1075cc motor. If you are going to use a 900cc block you
can get a 1015 block or you may as well go with a 1200cc motor. A 1200cc motor
cost the same as any smaller motor that needs sleeves, so that's the biggest
bang for the buck. A 1075 is the smallest motor that I would have for myself.
The 1200 does have some drawbacks such as overheating in traffic. So do not
make this decision lightly. For the "first time" engine builder.
I would recommend staying with the stock cam as you break
the motor in for a couple hundred miles before installing the new cam. A good
street cam profile has 240-260 degrees of duration @0.050 lift. A very very wild
street cam has a duration of 260 degrees @0.050 lift. Light to light the milder
cam will win most of the time. On the Œ mile the wild cam will win. Make your
choice. Go with 34mm RS carbs for engines 1100cc and smaller. 36mm RS carbs for
larger motors. The heads really need ported to match the carbs and let the motor
breath. You are wasting your time and money if you fail to port the head and keep
the stock carbs. Note that you will probably need to use size 15 pilot jets in the
RS carbs, if you plan on running a header with a baffle installed. So buy them when
you get the carbs and replace them before you even install the carbs for the first time.
You can purchase a CD-ROM with my Old Kaws Never Die Series including
NEW chapters not available on the web site. My Race Engines and
Swingarms series are only available on this CD-ROM.
My Tips & Tricks FAQ is also only available on this CD-ROM
Includes the latest chapter on replacing the 1978 and earlier regulator and rectifier
with a modern solid state unit. Detailed step by step instructions with wiring diagram
All files are in PDF format, PDF readers are freely available.
The price is $19.95 and includes postage in the USA.
International Shipping costs more --> Total of $29.95 USD - Click Below For International Sales
Send email to the OldKawMan