“The World’s Quickest CT90? Possibly…”
Launched in 1966, the Honda CT90 was a single-cylinder four-stroke step-through bike additionally marketed because the Path 90. It might appear unusual in our day of purpose-built filth bikes and utility four-wheelers, however Honda really marketed the bike to hunters, farmers, outdoorsmen, and commuters, highlighting its off-road utility.
In actual fact, in a current retrospective, Final Motorcycling known as it “The First True Journey Bike,” interviewing an 80-year-old native of Michigan’s rugged Higher Peninsula who nonetheless makes use of his ’68 CT90 to roam his native logging roads and trails in quest of small sport.
Whereas manufacturing resulted in 1979, the CT90 had change into a mainstay Down Beneath:
“Honda killed off the Cub-derived CT fashions in lots of markets as prospects moved in direction of sooner machines, however the CT soldiered on in Australia because the beloved ‘postie bike’ for many years, serving as a mail provider’s mount. These bikes have been additionally in style in some African nations, as they supplied wise all-terrain functionality for under-developed highway networks.” –Journey Aside
With simply 7 hp accessible from the 89cc aluminum head OHC engine, the CT was no speedster, boasting a high velocity of simply 55 mph. Nonetheless, our pal Matt Sheppard of Adelaide, South Australia’s SXK Bikes (Sheppard x Kennedy Moto) — builders of the ’48 BSA salt racer we beforehand featured — determined to rework one in all these beloved outdated postal bikes right into a land velocity racer:
“This challenge was about all a few Postie going quick so was given the nickname the ‘Categorical Postie.’”
It’s really a 1974 CT90 engine in an ’82 CT110 body, extremely modified to compete within the 100-MPS-CG class, which means as much as 100cc, partially streamlined, traditional, working on common gasoline. Matt offers us the complete particulars on the modifications beneath, however suffice to say that turning an outdated mail provider mount right into a salt racer was no straightforward feat — particularly one that might accommodate Matt’s six-foot body:
“The problem with the CT90 as a land velocity bike is the truth that they have been by no means imagined to go quick. Every thing about them is designed for low-speed stop-start using to ship the mail. The CT90 even has a twin vary gearbox to make it fitted to even decrease than regular velocity using.”
Then there are the challenges that come up solely on the salt itself, working at WOT for 3 miles on finish. Nonetheless, Matt and his crew of Salt Monkey dry lake racers persevered to set a brand new Australian class file of 62.81 mph, with a finest recorded of velocity of 66 mph — a 20% improve from manufacturing unit! Says Matt:
“The objective is 70 MPH plus subsequent yr! As a enjoyable facet word, I can’t discover any information on a Honda CT90 with the usual engine going any sooner — is that this the world’s quickest CT90? Possibly…”
Under, Matt offers us the complete story on the idea, the construct, and racing throughout Australia’s Velocity Week at Lake Gairdner — aka “the large white dyno.”
Honda CT90 Land Speeder: Builder / Racer Interview
My title is Matt, I’m a 33 yr outdated bike mechanic from South Australia. I grew up adjoining to bikes however wasn’t bitten by the bug till my late teenagers. My uncle has all the time been a motorbike fanatic and a staunch Kawasaki fan; my early reminiscences of visiting him embody his Z9 parked proudly in the lounge.
I additionally rode his Seventies KE175’s when visiting however I didn’t personal my first bike till I used to be 19, the no-nonsense Honda CRF450. The CRF launched me on a steep studying curve. In comparison with the KE175, the Honda was a big step up in energy and weight additionally a number of my early using was in sand. Evidently I fell off rather a lot!
The following couple years noticed me off-road and enduro using till a profession change by work expertise in a bike seller uncovered me to a complete new world of motorbike. This led to an apprenticeship as a bike tech, which obtained me acquainted with highway bikes. It wasn’t lengthy earlier than I owned a Kawasaki ZX6R and spent all my free time using by the superb Adelaide hills.
In 2015 I opened my very own workshop as a bike mechanic, the place I started taking tasks restoring and modifying older bikes. My expertise discovered as a panel beater in my first apprenticeship have helped with the fabrication work. This shifted my curiosity from simply fashionable bikes to appreciating the classics.
This bike is a private traditional challenge is one thing I’d talked about constructing for a few years with a very good mate of mine for Australia’s Land Velocity Race at Lake Gairdner.
It’s a 1974 Honda CT90 engine in a 1982 CT110 body. In Australia the traditional Honda CT90’s and Ct110’s are generally generally known as “Postie bikes,” as they have been utilized by our postal service for one of the best a part of 50 years. This challenge was about all a few Postie going quick so was given the nickname the “Categorical Postie.”
The problem with the CT90 as a land velocity bike is the truth that they have been by no means imagined to go quick. Every thing about them is designed for low-speed stop-start using to ship the mail. The CT90 even has a twin vary gearbox to make it fitted to even decrease than regular velocity using.
In land velocity racing, bikes are primarily separated by engine capability. They’re additionally classed utilizing age of engine and gasoline sort. The CT90 (89cc) match within the as much as 100cc class, and as a result of age of the engine it match into the traditional class. It was run on regular gasoline.
Our first modification was to discover a piston that might take the engine to as near the 100cc restrict as attainable. After a little bit of analysis I discovered a piston from a CB175 twin, which gave me the proper bore measurement, gudgeon pin measurement, and the bonus of a a lot increased dome to lift the compression.
The mixture labored however the combustion chamber needed to be barely reshaped and the piston flippantly machined to cease the 2 from making contact. I additionally welded on some extensions to the cooling fins on the barrel to assist with warmth dissipation.
The top ports have been opened up a bit to match the brand new consumption manifold and exhaust, and a Yoshimura 28mm downdraft carburettor was fitted to feed the little beast.
A lot to my shock I additionally managed to discover a efficiency camshaft. Belief me after I say, there are only a few outcomes while you seek for Honda CT90 efficiency elements!
I selected to run it within the Modified Partial streamlined (MPS) body class, which meant the bike might be fitted with a entrance fairing however not aerodynamic aids on the rear.
The body was raked and rear shocks have been swapped for some stable struts. This lowered the bike whereas barely lengthening the wheelbase however throughout the 10% allowed. The stable rear struts additionally allowed the rear tyre to be tucked up contained in the lengthy rear fender for much less wind drag.
The fairing used was designed for a Yamaha RD350, which the store purchased some time in the past hoping to make it work for one more challenge. I sat it over the body as a little bit of amusing and rapidly seen it match very properly.
To minimise wind drag I needed the bike body to be stored as slim as attainable and hold my physique contained in the strains of the fairing. The usual CT90 tank is sort of extensive with the seat sat on high. This is able to have my knees within the breeze, so a brand new slim tank was made out of some chrome steel and a really small and never so luxurious seat sat behind it.
I additionally made some new handlebar mounts that introduced the bars from above the highest triple clamp to in entrance of the forks. This together with the foot pegs shifted way back to the foundations allowed, helped get my six-foot body considerably tucked in. An entire bunch of different small requirements and a coat of paint and the bike got here collectively properly.
I solely began actually moving into the construct a pair months from velocity week, so it was all the time going to be just a little rushed. I completed the bike the day earlier than we left so I hadn’t actually had an opportunity to run it anyplace or spend any time on a dyno, however with our fingers crossed we headed to the salt.
On Monday, our first day of racing, I managed three runs down the salt with a finest velocity of 59.6 MPH, however the bike skilled some gasoline hunger points. Sadly, these are points that you simply solely discover with a wide-open throttle for a mile or two, which is why I hadn’t come throughout them within the store.
In land velocity racing there’s a two-mile run up, adopted by one mile which is timed. With my gasoline hunger downside, I may trip at full noise for many of the run up however by the point I obtained to the timed part the engine would splutter previous 3/4 throttle. As disappointing because it was it gave me confidence the engine had extra to present.
To beat this problem, I lifted the gasoline tank barely, rerouted the gasoline strains, and made a makeshift ram air gasoline tank pressurization system with a funnel and a few tube. Sadly, the rain got here in and I needed to wait two days to check my alterations.
As soon as the rain had handed and it was my flip to trip, I logged a velocity of 59.5 MPH and located the fueling issues have been resolved by the pit modifications.
I did, nonetheless, discover that my Seventies electrics weren’t having fun with the extremely corrosive setting and my ignition system began giving me a misfire that solely obtained worse because the engine obtained hotter — once more the problems would solely change into prevalent by the point I made it to the timed part of the monitor. I made a decision to maintain my last trip for Friday to reap the benefits of cooler circumstances and I used to be rewarded with a timing ticket of 66.06 MPH.
This gave me the common velocity from the 2 runs at 62.81 MPH, which is now the Australian file for sophistication 100 MPS CG. I’m but to get an influence run completed on a dyno however it is going to be attention-grabbing to see how a lot I’ve improved on the 7HP the manufacturing unit tells us it had, however with a finest recorded velocity of 66mph I managed to up the highest velocity of the bike from manufacturing unit by 20%.
For subsequent yr’s race I’m changing the ignition system with one from this decade, becoming a smaller rear sprocket, and bettering the bike’s ergonomics. The objective is 70 MPH plus subsequent yr!
As a enjoyable facet word, I can’t discover any information on a Honda CT90 with the usual engine going any sooner — is that this the world’s quickest CT90? Possibly…
- Shark leathers for doing an superior deal on some customized race leathers
- Saint.cc for his or her assist with this challenge and others
- Shed King Adelaide
- All of the crew and crew of the Salt Monkey dry lake racers.
Comply with the Builder / Racer
Picture credit the place famous: Patrick O’Kane of Eye See Pictures