Retrospective: Kawasaki 350 S2 Mach II Triple: 1972-1973

Here was the successor to Kawasaki’s kick-butt A7 Avenger 350, a two-stroke twin using rotary valving. When the A7 appeared, the factory claiming some 40 horsepower, the quarter-mile fanatics were going through the lights in under 15 seconds.

Not bad. But Kawasaki engineers understood that two-stroke power comes from porting and being able to cram more fuel into the combustion chambers…three smaller cylinders offered more porting possibilities than a similar-sized twin.

1972 Kawasaki 350 S2 Mach II
1972 Kawasaki 350 S2 Mach II

But rotary valves? Sorry. Doable on a twin, but no way could this be done on a triple without making the engine too wide. So the triples reverted to the tried-and-true piston-port design, which is not only simpler to build, but has better lubrication because the gas-oil mixture spends more time down in the crankcase before going up to the top of the pistons.

The cylinders were aluminum, with cast iron liners, and the pistons fired at 120-degree intervals, making for a smooth engine. Bore and stroke was an almost square 53 x 52.3 mm, with maximum power coming on at 8,000 rpm, redline at 8,500. Thirty lb-ft of torque came along at 7,000 rpm, so there wasn’t much grunt at low rpm. Three 24mm Mikuni carburetors sent the gas to meet with the oil from the Superlube system, controlled by both engine rpm and throttle position. The oil reservoir held five pints, the gas tank, 3.7 gallons.

The S2 was a product of superb machining techniques, with horizontally split cases housing a pressed-together crankshaft using multiple main bearings, three connecting rods and three pairs of flywheels, all tight as the proverbial drum. One of the big concerns was always the carburetion, which needed to be spot on, and the crankcase’s three separate chambers were all part of the system. Any air leak could prove disastrous, and sophisticated rubber seals kept the mixture as it should be.

1972 Kawasaki 350 S2 Mach II
1972 Kawasaki 350 S2 Mach II

This minor technical overview really relates to all the Kawasaki two-stroke triples, not just the S2 being described here. There sure were a lot of the triples, beginning with the 500cc H1 Mach III that appeared on these shores late in 1968, to the final 1977 KH400—and who knows how long these bikes were sold in other parts of this far-flung world. The 500 H1 was joined by both the 750 H2 Mach IV and the 350 S2 Mach II in 1972, and then the 250 S1 Mach I in 1973, with the S2 morphing into the 400 S3 in 1974.

This Retrospective is about the 350 version, the S2, which had the shortest run of the lot, only two years. With reason, as will be shown. When Kawasaki began developing the triple concept back in late 1966, the engineers were after one thing, and one thing only—power! Back then, 60 horses out of a 500cc engine was astonishing. So maybe the factory exaggerated a bit, but when a Mach III rider could do the quarter-mile in the low 13 seconds, people paid attention.

1972 Kawasaki 350 S2 Mach II
1972 Kawasaki 350 S2 Mach II

Three years later came the (alleged) 74-horsepower Mach IV and (alleged) 45-horse S2, and magazines promoted the S2 as being the most civilized of the trio—and by comparison it was. Back in the early ’70s the 350 racing class was a popular one, both on a club and professional level, being a lot cheaper and somewhat less dangerous than the 500s. Also, some European countries had licensing and tax breaks for motorcycles under 350cc. In the U.S. it did have a price advantage, costing just under $900, while the 500 went for $1,200.

Price was of concern, so the S2 had battery-and-coil ignition rather than the more expensive CDI seen on the 500, and a drum brake up front rather than a disc. No need for a big battery, as the S2—and the others—had a kickstarter. Which an anorexic 90-pounder could kick over with ease. The ignition switch was conveniently up by the speedo and tach, with the spring-loaded enrichener for cold starts right by the throttle. This enrichener had to be held in place to avoid forgetting about it and then fouling plugs, and the bike might need a warm-up of a minute or two on a cool day.

1972 Kawasaki 350 S2 Mach II
1972 Kawasaki 350 S2 Mach II

A major difference was that the 350 had some pretense at handling. The frame was a standard double cradle of moderate stiffness, using tubular alloy steel. Up front, the telescopic fork had good springing and rebound damping and was perfect for a solo rider…like on a racetrack. At the back, the shocks had excellent rebound damping and were preload-adjustable. Dry weight was a lightish 330 pounds, more than 50 pounds less than the 500. Wheelbase was short 52.4 inches, the 500 being 55 inches. The Mach II was an entirely flickable bike, with the narrow engine (two inches less than the 500) giving it great cornering clearance.

Essentially, this was a bike that wanted to run at high rpm, with a manual steering damper up by the instruments to aid the speedy types. Full tilt was better than chugging around town, as the throttle had a long pull and if the rider twisted the throttle too fast, the engine could bog…which is why extra plugs were under the seat. Get it up into the six- to eight-thousand rpm range and it was downright fun. Styling was cool, with the long tank flowing into the two-people seat that ended with a sporty kick-up at the very end. The hinged seat lifted up to reveal a tail-box big enough to house tools, extra spark plugs…any small whathaveyous. And there was a very respectable taillight, large enough to keep tailgaters at bay. The handlebar was moderately high, as Americans liked them. The exhaust system had one pipe on the left, two on the right—that look was already instantly recognizable due to the 500. “Wow! That’s one of them triples!!”

1972 Kawasaki 350 S2 Mach II
1972 Kawasaki 350 S2 Mach II

 

A couple of drawbacks: As noted above, Kawasaki was claiming 45 horses and a top speed of 112, but no magazine tester could even get it to 100 mph. Also, it was a thirsty wretch, and if the rider kept the throttle full open he was looking for gas in less than 100 miles. The second problem was the twin-leading-shoe drum brake on the front wheel: Two strokes do not have much in the way of compression braking, and during a spirited ride the brake would begin to fade.

Kawasaki took care of the brake problem by installing a disc late in ’72. But the company, feeling it would sell better as an urban machine, enlarged and detuned the engine, creating the 400cc Mach II in 1974. The horsepower was officially degraded to 42—and the miles-per-gallon were greatly improved.

Year/Model: 1972 Kawasaki 350 S2 Mach II; Owner: Steve Davis, Arroyo Grande, California.

(This Retrospective article was published in the December 2012 issue of Rider magazine.)

27 COMMENTS

    • I had the S2 350 in the early eighty’s. It was a barn find that I found and rebuilt. With a cafe fairing it would top out at 120mph.

  1. Had a late 72 with the disk brake. That bike would run easily run over 100 mph. Wish I still had it. Great Fun! Replaced with a 1976 KZ900LTD, which I still have!

  2. I rode a 350 S2 for about four or five months. It was fairly well used and a theft recovery a friend who was an LA County Sheriff got at the impound yard… cheap. He rode it once, it scared him, and he bought a Kawi 400. I ride the 350 with him for a while and when he was ready to sell it, I painted it for him.

    The bike was insane. I mentioned that it got about 12MPG to a salesman at a Kawi dealer, and his replay was, “That much, huh?” I imagine that worn components were a possible cause, but at 80mph it felt like riding on ice. With it slowly rotated back and forth on its center axis about four or five degrees- first a little clockwise, then a little counter clockwise, then back.

  3. I bought one of these fantastic bikes new in 72′. I got it up to 110mph! This bike was a smooth / fast ride. Shut down many bigger displacement bikes on a daily basis. Wish I still had it. Got totaled in 72′.

  4. I was 14 years old, working as a busboy in a restaurant for $1.00/per hour and I could not sleep or eat because this exact same bike (candy apple red with a matching helmet) was consuming every thought I had. My dad finally gave in and co-signed on a loan for it. I remember it was in the early spring in Grand Rapids, MN and I drove it home from the dealer (Goldfines). I nearly killed my self on a patch of ice on the way home but made it without wrecking me or the bike. I WAS IN HEAVEN!! I remember getting to about 107 miles an hour on this thing while I was laying down on the seat with my legs out straight behind me. I thought I was going to pee my pants. I am 60 years old now but I will always remember this bike with fond memories. One of my friends at the time (later grew to be one of the US Hockey heroes from the Miracle on Ice -Lake Placid Team) borrowed this same bike for his motorcycle training/testing permit. Nothing but fond memories (and a lot of fouled plugs) of my younger years and this motorcycle. Thanks for the article.

  5. i had a 1973 350 s2 “back in the day” i drag raced it at island dragway in nj every weekend. bored it 1 size over within the stock rules, had bill werges pipes on it, kept my weight at 120lbs. won a wall full of trophys, and went on to set a national record of 13.02 time and 99.9 mph at sandston va nationals. could have done better with better gearing. 🙁 sold it for a 1974 900 z1. i have tried to buy it back several times a year but the buyer has the whole bike on his wall. ??? would be more appropriate on MY wall. lol also drag raced a 1973 kawasaki 750 triple……widowmaker!!

  6. Bought a new, blue 1973 S2 when I was 18 yr old. I hand polished and matched the intake manifolds, which may or may not have made it faster. Had it up to 115mph, to see how fast it would go; let off then. It was still accelerating slowly, but it wouldn’t have gone much faster.
    A buddy of mine had one as well. The “fastest” RD in town wanted to race him (they were supposed to be faster). He thought he would take him but, as mine was considerably faster, he asked me to run him instead. I pulled him 20 ft in first gear and was gone.
    Another buddy with a ’71 CB750 couldn’t even think of keeping up with me in the twisties.
    It was an amazing bike, drove it for 3 years and, regrettably, sold it.

  7. Bought my S2 350 new in 1972. Was working at a Dairy Queen for 85 Cents per hour. Going to school working 50+ hrs a week nights and weekends to pay for it. WELL worth it. I put over 4k miles on it my first and only summer and drove up to 6th Nov in Canada until a beginner driver in a big Ford car took me out.
    Miss the bike, miss the sound, the blue smoke, miss the fouled plugs. Use to rotate my spark plugs at least every 2 weeks. Back then could take them to the dealer and put the base of the plug in a plug size hole in bag with graphite hooked to air compressor 10 seconds and were like new.
    Now have Suzuki Intruder 1400cc but still miss my little buddy. Top speed for me was 107 mph but was light and started to wobble. Went to 100 mph anytime I wanted but got scared earlier to push up to 107 again. I remember as a 16 year old kid people would ask “How fast will it go” and I use to answer..” I don’t know but by the time you see where you’re going.. you already been there”

  8. After Vietnam I had a Yamaha ’67 YR1 350 that I rode from Monterey, CA to L.A. every weekend. Had that bike for over three years and racked up over 100k miles on it. Sucker was so over-engineered all I had to do was tighten the chain, change the plugs and use good oil and it never saw the shop. I thought that was the typical 350 at the time. In ’76 I bought a 1972 Kawasaki 350 S2 Mach II and I’ve never had a bike that scared me like that one. I could be doing 60 mph, pop it into high gear, hit the gas and it would lift the front wheel off the road !
    Worked in Canada for three years and had a 650 Yamaha that was reliable as hell, but after the Kawasaki it felt like a turtle in high gear.

  9. I had a ’73 for a while in the early’80’s when I was in college. It was fun to drive if rpms kept high. Handled and performed better than all the twin 400’s and 500’s that my friends had at the time. But she sucked up a lot of gas and was not comfortable to ride on long trips. Perhaps mine had original sprockets changed because it redlined at 60 (I lived in a hilly/mountainous area so perhaps original owner was looking for easier starts up hill). If you weren’t paying attention when the powerband kicked in while going up hill in lower gears it would pull front wheel quickly off the ground and things could get out of hand quickly. Her life ended abruptly (and mine nearly did as well) when an oncoming car turned left right in front of me and we T’boned the car.

  10. I was stationed at Tinker AFB and had the first one to hit Oklahoma City in ’72 – Traded in my Honda SL350 for it. Couldn’t make it to Tulsa from Oklahoma City on one tank of gas and my car (’71 Pinto) got MUCH better mileage.

    Wish that I still had both bikes. ANd the next one down the line – a yellow ’75 Ducati 350 Desmo monoposto that I got while stationed in Italy.

    Sigh…

  11. bought a 77 kh400 new as my first bike at 17 yrs old…..worked 2 yrs part time to pay for it.what memories

  12. My brother had a ’72 S-2 in his garage for 15 years. He put some fresh gas, plugs, and a new battery in it and it started on the first kick. He let me have it for the price of the battery and I had a lot of fun with it until I sold it in ’93 for $50. It was only running on two cylinders when I sold it. It was almost as fast as the 500 triple I had when I was 18.

  13. I bought a S2 in 1972 and my buddy bought the 750. Those were the best years in my life. I painted mine canary yellow with snakes in the tank and side covers. We both extended the fork tubes 10 inches. We thought we were cool.lol. Both of these bikes had power but the 750 was scary fast. We both ran many a wheelie through the main strip in town, especially when girls were watching. I miss those days.
    Here is my nephew on mine in 73
    https://imgur.com/DikHehR

  14. I saw one of these in 1972 parked on the side of the road as i was walking back home,
    i remember i told the owner what an incredible looking bike he had but he just looked at me
    with a suspiciously look on his face lol! in 2016 i contacted him just to see if he still owned it
    but no luck, but he invited me to show some nice pictures of the same bike in his old foto album
    with a cup of coffee. Shortly after the visit it came up one for sale just a few miles from me!
    it was one of the only 61 imported to Sweden in 1971, i could not resist to go and take a look at it and a few
    days later i was the new owner. Better late than never! it was almost winter but i took it for a test drive
    round the block, during 2 years now i am doing a restoration of it to look as good as i remember it when i was
    young in 1972.

  15. I bought a new ’72 S2 in the Atlanta area; my friend had an H2. His was faster, but mine was the fastest bike I had owned at the time. The first day I bought it, it quit on me; it was out of gas. My bike had about a 60 mile range, and got about 20 mpg.

  16. It was a real pleasure reading all of your fantastic experiences with the rare kawasaki s2 mach 2 350cc triple. I was blessed with the chance to obtain one from a older woman who’s husband died and was told by her it was his pride and joy….i almost passed it up because the previous owner had stored it with light clear oil. Coated all over the motor rims and other metal surfaces….
    Which over the years since it has been parked since 1979 had attracted and held dirt and dust and the bike looked terrible…just when I started walking away I took one more look at it as I walked away from behind and instantly knew when I saw the two pipes on one side and the one on the other just what was before me…oh my god…its a giant slayer…kawi tripple. I began to shake and tried not to show my joy….and made the deal. When a got it home a covered the pipe ends with plastic bags and elastic and took it for a power wash….i didn’t realize that the oil sprayed on it was recommended by kawasaki….but it cleaned up like a diamond and the oil had kept the chrome and rust from adhering to it. I now have along with this 73s2 a 72 yamaha r5 350 twin and a 72 yamaha ds7 250 twin and I am in the process of tryn to obtain a 71 Suzuki t500 cobra twin….these old two strokes have stole my soul and now own me. I was reading and seeking information on this t500 cobra Suzuki that I’m tryn to get and that was my reason for being on your website which I found very helpful and informative for me. Thanks for listening and for providing such great material for us enthusiasts. Ricky ,aroostook county maine. Usa

  17. I just landed a late 72 with the disc brake. Somebody painted the frame and the panels with a nice garnet red. She runs like a scared rabbit and I love the sound of the screaming 2-stroke triple. So glad to have this little runner. traded a 76 RD400 for it, and I’m not sorry.

  18. I had a 1972 S2 350 Kawasaki triple. I bought it new. The only problem with it was the footpeg bolts. I would constantly wear them out and the pegs would fly off. I was also ARRA#8 for two years. Maybe that explains it. Robert Radel 65yrs. old.

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