A 1979 Honda CB750K to be exact. I'm gonna convert it to electric, but first the story of HOW I GOT THE THING:
So fellow MITERS denzien Bayley decided to buy a for-parts 1982 CB750 for $250 off of Craigslist. His goal is to use a Prius motor controller to drive a Ford hybrid motor, and get an effective electric motorcycle. Often called the first superbike, or "King of Motorcycles", the CB750 (first produced in 1969) is a legendary motorcycle for being the original Universal Japanese Motorcycle (UJM). It was also one of the first commercial motorcycles to sport four separate carburetors (which mix gasoline and air in preparation for cumbustion), a straight 4-cylinder single overhead (later double-overhead) cam 75-horsepower (~50Kw) engine, an electric starter, turn signal blinkers, a 5-speed transmission, front disk brake, etc all in one ~$2000.00 (in 1969 dollars, which is like $12,000.00 today) package, which was unheard of at the time. With a top speed of 125 mph and plenty of motor torque, this bike can soar.
Many people like the badassery associated with Kawasaki Ninja type motorcycles, but I've always wanted a classic-looking motorcycle. Not WWII classic, but one like the one above (from the US version of The Girl With The Dragon Tattoo). After researching the CB750 and hearing Bayley got his for $250, it also had my attention.
Now, before Bayley found the Prius controller, he was going to use a Sevcon Gen 4 motor controller on it. This controller is found in commercial electric vehicles, and is a favorite among EV enthusiasts. I've been on his back lately about finishing the Melonchopper custom motor controller, but it seems the magic transistor he was going to use is still unavailable. Imagine my surprise when he just says "here, have a Sevcon 4!" and hands me a $925.00 motor controller!
Looking through the specifications of the controller, it can output 350 Amps peak at up to about 96 Volts (~35kW!!!!!!!). However, it seems the 80mm-class "melon" motor which powers Melonchopper is barely powerful enough to take advantage of the what the controller has to offer: a waste of a $1k controller Bayley handed me for free.
What should I do with this Sevcon Gen4 controller? Should I perhaps build an electric motorcycle? Where can I get my hand on a good enough motor? As with most things, I consult my good friend and mentor Charles Guan, but he didn't have to do much convincing: next to him sat an electric motorcycle that was undergoing some maintenance.
The motorcycle belonged to an IDC student Lennon Rodgers, who documented the entire build on his website, electricmotion.org. Charles said there was an ME0907 etek-style motor lying around MITERS up for grabs, which can draw 220 Amps peak, 80 Amps continuous at 72 Volts, for a peak power of about 18 kW (about 25 horsepower, a third the power of the CB750 motor), nearly 3 times as powerful as the "melon" motor.
And so, I decided I'm doing my own EV conversion of a motorcycle. I have the knowledge and experience, a decent (and free!) motor controller capable of putting out 35kW peak, a decent (and free!) etek-style motor capable of handling about 18 kW peak, access to a number of machine tools, and a rewarding summer job. When Bayley offered to lend me his craigslist-scoping skills, I took his offer. Within minutes, I was looking at a Craigslist post for a for-parts 1979 Honda CB750K for only $100. I took the offer.
The next day after work I went to Revere, MA to pick up the motorcycle, UHaul motorcycle trailer in tow, accompanied by both Bayley and Thomas Villalon (interning with me at Aurora Flight Sciences this summer and a member of the MIT Solar Electric Vehicle Team).
And here she is! Exactly as ordered, a CB750 worth $100. We tried to start the engine with the seller's handheld car starter, to no avail. It's either bad wiring, a faulty starter, or a seized motor.
At least the rear drum brake works! The front disk brake needs to be tuned, but should be okay. The frame, tank, and body looks alright, surface rust is nothing a little sanding and repainting won't fix. I'm really digging the two-person leather seat, and the wheels and tires look to be in good shape as well.
Here she is ratchet strapped and otherwise rigged to the motorcycle trailer.
The seller also gave me a spare front kit from another Honda cycle (with a headlight and blinkers) as well as a saddlebag frame addition and two hard-case lockable saddlebags (In which I may store extra batteries for higher range).
Arrival at MITERS
Thomas checking out the bike with the add-ons thrown on it. $100.00 was a pretty good deal for everything I got!
Here it is with just the seat on. Sexy.
The next day I decided to run a random check of how things are working out. If it isn't difficult, I may go the Mikuvan way and at least attempt to get the engine running. First thing I noticed was there was no throttle, just a box with the steel cables. Also, the choke (which controls how much air goes into the fuel-air mixture) seemed to not want to budge.
To check under the hood, you use your key to remove the seat and access the battery area.
Part of the seat adapter was bent out of shape, so I'll need to make sure that gets back on correctly. I also need to clean out some of the rust on the underside of the seat.
The fuel tank just... comes off. 0_0 I was expecting there to be some sort of cable I have to remove, or for the gas to start pouring out the moment I removed the tank, but nothing.
And here's why: the fuel movement from the tank to the carburetors is controlled with this valve here, located under the tank, and it is currently turned shut. But how does fuel get from here to the engine?
Oh. Fuel line's cut.
At least there's oil in the... OH WAIT. THERE IS NO OIL BECAUSE THERE IS NO OILPAN INSTALLED ON THE BIKE. The entire bottom of the transmission is simply... open. At least I don't need to drain it!
As for the electronics/lights on the bike, most of it looks like this. It's manageable, and all of the colors for the wires are detailed in the manual, but still kind of annoying.
The front brake doesn't seem to do anything, so I need to drain and replace the old brake fluid. The manual seems to detail all.