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I have a complicated relationship with this motorcycle. This 1981 Honda CM400 Custom is actually my wife’s bike. We bought it last spring for not a whole lot of money, and at the time we thought it was in pretty good shape. It wasn’t just her first motorcycle, it was our first motorcycle. Jeff and Ryan here at BlueCat had given me some great pointers on what to look for in buying an old japanese motorcycle, but I still didn’t really know what I was doing. Jeff set me straight in a hurry though when we brought the bike in for a quick evaluation. It was poppy and running lean. The tires were rotten and split, even though there was plenty of tread left. The chain was dry and rattling. Worst of all, the carbs were consistently dripping fuel.
Over the course of four months I changed tires, chain and sprockets, and fiddled endlessly with the carbs. With Jeff’s help, I finally got the fuel leak sorted out myself and everything seemed alright. The CM ran, finally. It didn’t run great, but it ran well enough to ride. That is, until September when it blew a head gasket in spectacular fashion 40 miles out of town. Fast forward to late January, when we finally got in on the lift here at BlueCat to see if we couldn’t breathe new life into this ailing machine.
We pulled the seat, the tank and the carbs and finally the valve cover. This bike only has a little over 6000 miles on it, so everything is still nice and clean in the top end. As this was in part an instructional exercise for my benefit, Jeff put me to work wrenching along with him — pointing out key things as we went. What I noticed right away was just how fast Jeff is at attacking the mechanicals. The man is a maestro with a socket wrench. There would be a flurry of motion and in a flash the valve lifters were up and out of the head. With another flash of the wrench, the stud bolts were out. We bagged all the parts and bolts, then tied up the cam chain, careful not to drop it into the engine casing. Soon the head and the cylinder were set out on the lift and pistons were laid bare, sticking up awkwardly from the crankcase like a pair of angry little baby birds.
We were inspecting everything in the top end of the engine because, “hell, we’re already in here.” The cylinder walls looked great, rings were in good shape and the valves didn’t need any resurfacing. Since we’d disturbed the cylinder studs, we went ahead and replaced the bottom gasket as well. That, after some heat, some careful prying, then lots and lots of razor blade scraping. With a few dabs of motor oil and moly grease, the motor went back together without a hitch. I bolted the carbs back on and everything seemed perfect. That is, until we started it up.
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