Honda CB350 "Sunfire"

My first motorcycle build project.

Specifications and Build Info

Chassis	1971 Honda CB350
Engine	325cc parallel twin. Complete dis-assembly and rebuilt with new seals and consumables.
Front End	2007 GSX-R 600 Inverted Fork.
Brakes(Front)	Hayabusa 320mm Rotors paired with Tokico calipers from a GSX-R. (Rear) Drum brake.
Ignition	Probe Engineering CB350 electronic ignition with electronic advance.
Chassis Wiring	Motogadget M-Unit with brand new wiring. All lighting is LED.
Fueling	Mikuni VM28 with Airpods

Engine and Fueling

The engine is mostly stock, 325cc parallel twin. The engine was completely torn down and rebuilt with new seals and other consumable parts. While the engine was disassembled, we cleaned the engine to remove the many decades of grime and dirt that had accumulated.

The decades of storage had not been kind to the stock Kehl carbs. The diapgrams had distingerated to dust and other parts had corroded from the elements, gasoline and other unknown elements. Rather than tru to restore them I decided to throw them out and go with new carbs.

Mikuni VM28/30s

Electronic Ignition

As part of my goals of making the bike run better and more reliabliy than it did when stock, I tossed out the old points ignition, condensers and coils. In their place went a modern electronic ignition system manufactured by Probe Engineering. The system is composed of a sealed microcontroller unit that is wired to a hall-effect sensor pickup wheel that is attached to the camshaft. This also is calibrated to provide cylinder position data to the microcontroller unit, so the need to set advance and perform ignition is entirely computerized.

1400cc Hayabusa brakes on a 350cc bike

The 350 received a donor front end from a GSX-R 600. This meant the old wheel/drum system needed to be replaced as well. Because I began this build before Cognito Moto started offering their disc front hub, I had to put together a wide variety of parts with some custom machining work. The hub came from a Harley Nightser because it had the correct 25mm thru-axle, drilled for spokes and had disc rotor mounting surfaces on both sides.

However, the bolt pattern for the rotors did not match up with GSX-R rotors. Making things worse, the GSX-R rotors had a lot of material removed around the mounting holes making it impossible to drill them with the proper holes.

Google-fu showed that some other builders who were taking the same approach had discovered that Hayabusa rotors had enough material in the center to drill the Harley bolt pattern. So those could be mounted to the Harley hub. But there was another complication. The Hayabusa rotors are 320mm while the GSX-R rotors are 300mm.

That meant the Tokico radial calipers needed to be set back an additional 10mm so that the caliper pads would bite on the proper part of the rotors. 10mm spacers were machined and put in place.

The end result? A rather lightweight 350cc bike has twin 4-piston calipers biting down on 320mm rotors – a setup designed to slow down a 1400cc hyperbike. It is safe to say that there is no lack of braking power.

Electronics

The complete wiring harness of the 350 went through several iterations as my electronics/wiring skills improved. I started out with the original wiring harness, applying fixes wherever it was called for. However, due to the fair amount of customization I did and the upgraded electronics for ignition and charging, meant that a lot of the original OEM wiring could be removed and that other new, wiring should be added.

I eventually replaced all old wiring with new ones. It worked well for a year or two. Then I went back and revised the wiring again with the goal of reducing the total wiring using, and making it look “cleaner”. I also introduced the M-Gadget which centralized a lot of the electronic functions of the bike and helped me eliminate a lot of wiring.

The electronics box also contains a lithium ion battery. It is not a big battery due to the fact that there is no electric start, and the battery is only needed for lights and ignition.