TOPIC:

I raced my 1978 KZ400-B1 all season and was running consistent 16.8, bone stock. Managed a third place finish for the season. Even though it's my slowest bike, my friends and I now refer to the 400 as "the race bike."

Although I feel like making the other guy wait at the tree for 7 seconds has been part of my success, I'm looking for some recommendations to make this thing run a bit quicker down the strip, without changing the looks of the bike too much. Low 16s would be incredible. One idea I've seen is adding a toggle switch to turn off the generator when racing. 

Some current thoughts are a "dished" seat, more like the RS seat, some sort of rearset, and maybe lower bars. 

Also wondering about things like advancing the timing, etc. 

Please let me know your thoughts. 

How about a wheelie bar to keep the front end down during launch? 

wrote:

How about a wheelie bar to keep the front end down during launch? 

it's not that fast. And I still need to keep it street legal. 

Make a 6 year old your driver.
Run tubeless tires and no tubes to reduce your rotating mass.
Run alcohol.
Tune your exhaust for wide open throttle and slightly below WOT.

Advancing the timing will make less power unless you give it more air/ fuel mixture to burn during the combustion phase (bigger carb, bigger valves, longer duration cam etc) there is no easy power gains, everything is a compromise and needs to work together. To be honest tighter fitting clothes would probably reduce your times more than the mods you have mentioned by reducing drag 

wrote:

Some current thoughts are a "dished" seat, more like the RS seat, some sort of rearset, and maybe lower bars. 

Also wondering about things like advancing the timing, etc. 

Please let me know your thoughts. 

 

The dished seat and lower bars would help your torso act less like a sail as you go down the strip. You might consider a small bikini fairing to clean up the aero a little.

You mentioned rearsets. In the action shot you posted, what is supporting your left foot? It appears to be too high for the stock pilot peg and not far enough back to be on the passenger peg.

The 400 likes to spin, so let it: VM30s would be a good start, and you can give them large-ish main jets for strip use. Not sure what sort of exhaust is on there now - appears to be stock headers and aftermarket mufflers - but what goes in must come out so you'll need to pay attention to that too.

Years ago when I took my (non-stock) Super Beetle to the strip, I took the end cap off the SuperTrapp muffler. In theory I could have put it back on... Basically I'm suggesting mufflers that have a removable baffle or something you can take out while at the strip and then put back in to ride home.

Also think about gearing. Not sure what your sprocket tooth counts are, but going a tooth smaller on the front and/or 2-3 teeth larger on the rear will help it pull harder but at the expense of higher highway RPM.

wrote:

Advancing the timing will make less power unless you give it more air/ fuel mixture to burn during the combustion phase (bigger carb, bigger valves, longer duration cam etc) there is no easy power gains, everything is a compromise and needs to work together.


 

The only performance cams I've found for the 400s are hideously expensive: $500US

webcamshafts.com/pages_vehicles/motorcycle/kawasaki/579.html

 

First nice stable of bikes you have.  Second, not sure if you have seen this or if it will be of any help to your quest but check out this link with some IMO interesting suggestions. 

kz400.com/racingFrameset-5.html

Before you change anything you might simply try a tank full of ethanol free gas. It does burn with a bit more energy than ethanol pump gas. It may give you a few more tenths, or it may not.  Good luck.

wrote:

To be honest tighter fitting clothes would probably reduce your times more than the mods you have mentioned by reducing drag 

Agree with Wookie58 ^^^^^ .    Also, lower & narrower handlebars would help.  Not sure if a dished seat would be of value, as it might prevent you from sliding back to achieve a more aerodynamic position.  You need to get your torso down low, as best as possible, elbows tucked in.  Do the rules allow you to remove the rearview mirrors?  Anything to lower your drag coefficient will help.

Also, what gear are you in when crossing the finish line?  For lowest E.T. you want to be revved out in your highest gear on the top end.  And, make sure that you add enough teeth on the rear sprocket (and/or remove teeth up front) so that you're truly on the top of the powerband.  You don't want to be crossing the line halfway into powerband  and still accelerating.  

And, I'll take @urankjj advice on fuel one step further.  If available, try some 100 octane unleaded race gas.  Sounds crazy, I know.  Your motor does NOT need the higher octane rating, for sure.  However, the rate of evaporation is a whole lot faster with the race gas, giving a cooler charge to the motor.  A simple experiment to perform which might give a surprising improvement.

Hope this helps.  

Mike



 

I've raced my mostly stock kz1000 for years.  My first year out was one of the best and I placed second overall for the year.  That bike would run 12.20 - 12.40 in the 1/4 mile.  I won a lot of races due to the other guy red lighting.  My theory on this is the other guy gets really anxious when you "look" like you are already half down the track before they get the green.

I tried changing the front sprocket down one tooth and using stock, neither made a difference.  Stock gear I would pass the finish line in 5th gear, front -1, same basic time but in 6th gear at the end. 

What I did at the track was remove the mirrors, low air pressure in the rear tire for better hookup, and strap down the front end.  Strapping down the front forks made a small difference in take off.  Without the strap the front end would decompress on take off and I would wheelie off the line.  I have an open exhaust, no baffles.  If you remove your baffles to open it up then you really should also open the intake and rejet the carb to get any kind of effect.  I removed the airbox snorkle, the top to the air cleaner and I run a K&N air filter.

I hope maybe there is something above that helps you.