Blue Cat Motorcycle

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It’s a Honda CB250, eh. Part two.

Posted on 05 Jul 2011 in On The Lift | 0 comments

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In part one, Jeff and I had buttoned up the engine and carbs for a cool old canadian Honda CB250 — a bike with a romantic history. There was a lot left to do. The following Sunday afternoon, Jeff and I met down at the shop to get the CB250 looking more like a complete motorcycle. By the time I arrived, Jeff had the CB250 rolling chassis up on the lift and wiped down with foaming citrus cleaner. I wondered if he was going to hit any of the surface rust on the frame with paint of rust inhibitor.

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“Nah, I like the patina. Besides if I just hit the rusty spots, then the frame will be all spotty. You want to either paint the whole thing, or leave it alone.” Jeff said. I had to agree. The frame looked great, small spots of rust and all. It’s amazing how far clean can take you. Even still, we had a lot of work ahead of us before that frame supported a complete motorcycle. The handlebars were bent. The low-beam in the headlight wasn’t shining. The blinkers didn’t blink. The bike needed two new tires, a rear sprocket and a new chain.

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But where to start? With a lot to do, we started simple. We stripped the wiring and rotten hand controls off a set of donor CL350 bars. Unlike a lot of our rebuilds, we’re keeping the CB250 as close to stock as possible. That meant running the wiring through the inside of the bars. With the CL350 bars stripped down to chrome, we moved on to getting the heart of the beast in place: the motor.

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Even on a motor as small as the CB250, it takes two people to place it in the frame. Jeff laid out the mounting bolts and frame brackets on the lift and we were ready to roll. I grabbed the sprocket side and we heaved the aluminum lump into the frame. One bolt at a time we first shoved and then massaged the engine into proper alignment. I always think of these machines as being completely solid, unforgiving structures, but without a little give nothing would fit. A quick pry here and pull there, and all the bolts were in. We then spent about the next hour wrangling the foot pegs and exhaust pipes into place. The mufflers aren’t stock, but they’re pretty good Dunstall replicas, so we’re sticking with them.

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Time to divide and conquer. I started installing the carburetors and air boxes. Jeff started on the wiring by hooking up a battery box to chase down what was and wasn’t working. We found four bad blinker bulbs and the low beam of the headlight still didn’t work. Jeff pulled the wiring out of the bars and extracted what looked like mostly good wires. He re-routed the wires into the new bars and got them bolted down. Chasing the dark headlight into the switch, it was time for microsurgery. A strategically placed drop of solder had the switch sorted and continuity restored to the low beam circuit. However, the light still didn’t actually light.

While we had the switch apart, Jeff examined the wiring. The starter switch connected, and the brake light switch functioned properly. However, both were grounded to the handlebars, and the bars were rubber mounted to the frame. Where the hell was the negative ground? Solving mysteries on these old bikes is half the fun, but this was a real head-scratcher. For ten minutes, Jeff, Ryan and I tired to find that phantom ground. The solution finally surfaced, and when it did, it was so ridiculous that we all erupted in loud, profanity-laden disbelief. What the engineers at Honda were thinking is anybody’s guess. Thing is, I’ve been sworn to secrecy. If you want to know the mystery of early ’70s Japanese wiring, you’ll have to bribe Ryan for it. Be warned. It’s ridiculous.

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Tasks fell like dominos with the wiring sorted out. The headlight was back to two settings. Both carbs were clamped on and linked. Both air boxes were on with brand new filters fitted. There was finally oil in the crankcase. The final touch was the gold and white tank that had bought us the dead bike about to come back to life. The fuel lines were hooked up and we put petrol in the tank. The moment of truth had arrived. Would it run? Had we missed anything? We snugged down the plugs, hooked up the battery box and Jeff hit the starter.

The CB250 fired to life almost instantly with a very satisfying growl. Jeff felt the headers and pulled the plugs one at a time to ensure the motor was running on both cylinders. What followed was one of my favorite things to watch. Jeff began syncing the two carbs to each other and adjusting their idle mixture. On these older bikes, he has to do it mostly by sound. It’s an art and it’s really cool to see an artist at work. The engine note smoothed out, but got no less satisfying. The growly little twin on big pipes almost sounded like a two stroke. It ran great. It looked great. But how would it ride?

To be continued…

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