The KZ400 Drag Racer
By Mike McCabe
Mike on his KZ400 drag race bike.
Hmmm, what to do with that thing?
It began several years ago with my cousin bringing her bike over for a tune-up. I had been servicing motorcycles as a side line for many years and the old KZ was in need a bit of TLC. It wasn’t bad, a 1976 KZ400S, had only 7,000 original miles, and could be made road-worthy with little effort.......if you didn’t mind riding a pink motorcycle!
Well, as fate would have it she called me back one day and said “I’ve broken off with my boyfriend and I don’t want the bike anymore, what should I do with it?” We settled on $200us, I got the title in hand and out to the storage shed it went.
Some years passed, my children grew, and my son especially showed a keen interest in motorsports. I had begun a motorcycle drag racing effort about 15 years prior, but abandoned the project for other interests. After thinking for a spell, the decision came easily; we would transform the KZ400 into a drag bike. We would set modest goals, work on a small budget, and the primary objective would be to have fun, always fun.
Setting The Goals
Having some idea of what you want to achieve usually makes getting someplace easier and more fun, so it is that we needed to set some goals for the KZ drag machine. The number one goal of any racing effort, and especially drag racing is to achieve consistency. So it was decided that we would leave the powerplant factory-stock to begin with, and only when we’d achieved consistency would we then consider modifying it to gain increases in speed.
The only performance goal
that we set in the beginning is that we would work towards extracting every
last ounce of go from the stock engine. It was hard to know what to expect,
and speculation ran rampant in the building stages. A review of the specifications
page in the factory service manual did provide some numbers (and hope) to go
by, but they were little more than ink on a page until we got to the track.
For the record, the service manual claims that the KZ400 as produced by Kawasaki
would run the standing start 1/4mi. in 14.9sec. (KZ400S), 14.4sec. (KZ400D),
and 14.6sec. (KZ400D European). As you can imagine, these numbers sparked a
bit of interest and debate amongst fellow enthusiasts as the project took shape.
I had never seen a road test article that included performance testing like
the magazines do with all modern bikes today, so there was no way to know what
the KZ was really capable of. Only when I discovered Odd Ivar Bekkelund’s
KZ400 website did I finally come across an article that contained real-life
performance figures for the KZ400 (Everybike
Goes Bracket Racing), and learning that the production KZ400 was barely
capable of mid-16 second elapsed times has truly validated our efforts thus
Keeping the project within a reasonable budget has been absolutely key to enjoying our achievements and remaining true to our end goal - fun. It’s really not fun when the expenses outstrip the returns, and racing a 26 year old motorcycle that has never been regarded as a performance machine raised some concerns. It was obvious that spare parts for a 26 year old motorcycle would be prohibitively expensive through the dealer, so we decided it would be necessary to acquire a cache of spares to support our effort. To this end we began our search in the local sales flyers and soon struck upon a likely candidate. A bloke at a local air-force base had a 1976 KZ400D that he was done abusing, and after a brief discussion about his exploits aboard the trusty old steed we loaded in my truck for the ride home. The bike was complete, still ran (on 1 cylinder), and perfectly suited the objective of obtaining spare parts, all for the tidy sum of $125us. Then something really interesting occurred; while driving home with our precious cargo secured in the bed of my pickup truck we encountered heavy traffic. As we crawled along the highway at walking pace, a man in a van to our right suddenly began waving and shouting. Paying close attention now, we listened as the man said “hey, do you want another one of those” while pointing to the bike in the back of the truck. Well heck, of course we would! As it turned out, he had a 1975 KZ400 that he had disassembled many years ago, and we now had another spare parts bike for an even tidier sum of $50us, factory service manual included!
So now we had some things in place. We would shoot for consistency, we would get what we could out of the stock engine and we would keep the cost of going racing low. All that remained now was doing the actual work to make it happen. Ahh, the fun part!
The first step in making the KZ a drag-race specific bike was to strip it down to the bare essentials. All the road-worthiness components could be discarded, and this would help to lighten the bike and significantly improve the power-to-weight ratio. We completely dismantled the bike, removed everything that wasn’t necessary to run it down the track, and realized a weight loss of about 50lbs. As we worked we analyzed each component to determine if it could be modified for lighter weight. The seat pan was significantly lightened by cutting and drilling, as was the chain guard. Parts were weighed and compared with other parts, and sometimes decisions were based on performance rather than just light weight. This was the case with the front brake. Even though the drum brake system is actually lighter than the disc brake system, it was decided to go with the disc brake for the sake of braking performance. However, we did look carefully at the situation and realized a two pound rotational weight savings by slotting the stock rotor. As it sits now in its current configuration the bike weighs about 345lbs. With me on board it becomes about 550lbs., which with the stated rating of 36 horsepower makes for a power-to-weight ratio of 15.28lbs-per-horsepower.
To improve upon the riding position for racing purposes we constructed a pair of rear-set controls for shifter and rear brake operation. We now use what was the rear footpeg position as the footrests for the rider. We knew from the beginning that the riding postion on the short wheelbased KZ would be tough to run hard with any kind of consistency, so for the time being we flipped over a set of stock bars and bent them a bit to move the rider's position lower and more forward.
To help the launch off the starting line and the overall aerodynamics we replaced the rear shocks with tubular struts and lowered the front suspension to match. We dropped the bike down as low as possible and even cut a notch in the seat to lower the rider as much as possible.
We pared the instruments and controls down to just a tachometer and ignition switch, and then added another simple feature that would help extract everything possible out of the modest powerplant; We chose to keep a charging system on the bike to simplify the overall effort of keeping a charged battery on board, but installed a switch in the voltage regulator power wire to enable us to turn off the charging system when racing. The bike revs significantly quicker with the system turned off, and at the end of each pass I turn it back on for the ride to the pits.
The airbox was removed completely and we just run open carburetors, and the stock two-into-one exhaust that came on the 400S was modified to improve exhaust flow. We cut off the megaphone, shortened it, welded it back on and constructed a straight-thru baffle for it. Additionally we enlarged the main jets to accommodate the increased air flow, and just tuned the rest of the motor to stock specifications.
With the bike completely assembled and running it was time to find out what kinds of rewards we would reap for our efforts. Off to the racetrack!
We Go Racing
Ready for racing
We finally hit the racetrack in mid-July 2002. Our very first pass produced a email@example.com mph. A far cry from the 14’s promised in the service manual, for sure, but with practice it would surely get better. By the end of day one, seven passes later, we had produced a best time of firstname.lastname@example.org mph, and certain issues started to become clear. After three trips to the track and 21 passes it was obvious that in this configuration the old 400 wasn’t going to produce anything better than very low 15’s. The original goal of on-demand repeatability was still not a reality, and the specifications so boldy printed in the factory manual had been gleaned from a formula that did not include the weight of a rider, or were just plain hogwash. We wanted more!
Three things of detriment to the consistency aspect were glaringly obvious; The factory tachometer was wildly inaccurate, thus resulting in widely variable shift points. The transmission was notoriously prone to missed shifts, and the short wheelbase with compact cockpit made hard launches an exercise in wheelie control, sometimes to the jaw-dropping delight of any onlookers.
The shift point issue was easily solved by installing an electronic shift light with an adjustable box that triggers the light at the selected rpm. The shift light is a snazzy little device that has been stone reliable, and we’ve determined that the stock KZ400 engine likes to be shifted at 9200rpm.
The transmission has been another issue altogether. At the advice of several fellow racers we went to an electric-over-air shifting system, and we did so for at least two reasons. One is that it would remove the human factor from the missed-shift issue (if it indeed existed), and the second is we were hoping it would gain us that tiny bit we needed to break in the 14’s. I can tell you that it did neither. On one hand I guess it felt good that it wasn’t just me being a complete buffoon at the controls, but on the other it felt bad that the issue was going to be more complicated to solve than we’d hoped for. We are now the proud owners of a beautifully machined transmission that has been slotted and undercut specifically for drag racing use. It’s not in yet, but we have it ready to go.
We have also solved the wheelbase and rider position issues. The first thing we did was build a new set of handlebars that extend forward about 3.5 inches This moved some of the rider’s weight more to the front end of the bike, but more importantly stretched me out to a much more comfortable position for aggressive riding. The second thing we did was build an extended swing-arm, thus moving the rear wheel out from underneath my butt and greatly reducing the tendency of the front wheel to point at the sky when dropping the clutch at wide open throttle.
After 25 passes we finally got the bike into the 14’s, although not without a significant change to the factory configuration. In the stock configuration the bike would be going through the speed traps in 4th gear, sometimes just shifting 5th. To glean everything possible from the little 24 cubic inch powerplant it would be necessary to re-gear. We dropped the countershaft sprocket down to 14 teeth, and increased the rear sprocket to 50 teeth. What a difference! The first clean pass with this new configuration produced a email@example.com mph. So now we had broken into the 14s, but still hadn’t surpassed the factory claims, and by golly it certainly wasn’t stock anymore. The carrot was out there! We reset our goals to better the numbers listed on the spec page before we ventured inside the motor for more. Specifically we wanted to go better than 14.4 and eclipse 90mph with the stock engine.
Where we go from here
We now have 80 passes on the little racing machine and have reached our goals thus far. At the end of last season we ripped off several low 14 second passes in a row, with the best being a firstname.lastname@example.org. Several modifications are now in the works. We have built a new exhaust system for it which has slightly increased the primary tube size, equalized their length, merged them smoothly into a single collector and exits through a custom high-flow muffler. We have acquired a high performance camshaft from a company called Webb Cams who catalogs two grind options and reground our cam to the more aggressive profile of their offerings. I have done the calculations and milled a cylinder head .050”, thus increasing the compression ratio from 9.4-1 to 10.75-1. The head will also receive a good massaging in the ports to improve flow. We are hopeful that these modifications, along with the installation of the modified transmission will plant us squarely into the 13 second bracket.
We’re still well within a reasonable budget as far as we’re concerned and it’s become of point of pride with us. The total expenditures thus far, including the bike, spares, all the gadgets and a custom built flatbed trailer to haul it all is still under $2000us. That’s the complete package, hook it to the car and go. Most of the other racers paid more for their trailer. Granted we have to make practically everything we want for it, but that’s where a big part of the satisfaction comes from. True, I can just open the classifieds, shell out a few thousand dollars and be going in the 10’s tomorrow, but who can’t go out and buy speed?
How fast we go remains to be seen, but I can tell you that it’s been one ton of fun working with the KZ400. The fact that nobody really makes anything performance oriented for these bikes makes each successful modification that much more satisfying. The bike is a very popular attraction at the race track, even amongst the more serious competitors. It seems that everybody can relate to it in some way, and it never fails to bring a smile to an observer’s face. Spectators often stop by in the pits just to chat, and I like think that we may inspire some to go home and start their own effort with an old bike that’s just been sitting in the backyard unattended. There’s something about an older, smaller bike that’s attractive and endearing. They’re not intimidating or threatening, and even the toughest of the tough can’t wipe the smile from their face upon mounting one.
They’re just fun!
More drag racing pictures
This is Kenneth Siegner on his 1978 KZ400C on the start line. He is competing against a Chrysler Neon.
He ran a 16.4 of 3 runs before his clutch cable snapped. And he did beat the Neon!
Here is another 1976 KZ400 drag racing bike
This bike was put up for sale on Ebay at December 20th 2004, by Pirate Cycles, Austintown, Ohio, USA
These pictures are reposted with the permisson of Pirate Cycles.
Raked, stretched and lowered
Extended swingarm, about 8" over stock
Lightened, all unecessary parts removed
Accel coils and wires
Round bore Mikuni carburetors
K&N air filters
Welded clutch basket studs
New clutches, H1 performance springs
Custom made exhaust
Sun Star 47T rear sprocket
Fake tank (KZ400 steel tank, gutted, with gas cap and KZ emblems for the look)
Electric fuel pump
Charging system eliminated, still has electric starter to start bike.
MRE air shifter
MRE air pressure gauge
MRE handlebar mount with MRE air shift button
Summit Racing shift light with dial setting on rear of shift light
New front tire, good rear tire
Chassis was constructed to allow body parts to be quickly removed for any repairs or maintenance
And you will find more pictures here: http://community.webshots.com/user/piratecycles