David’s Yamaha RD500LC

David owns/runs an engineering company, so he doesn’t shy away from extensive modifications. With Brembo Monoblocs, Öhlins forks, a Deltabox-style frame and R6 swing arm this no longer looks like a 1985 bike. The frame is a skin welded over the aluminium box section frame version of the RD, which originally only went to Japan and possibly Australia. David made the custom exhaust and yokes too. And my old mucker Stan Stephens gave the engine the Stage Three treatment.

As David already has one RD500 he just wants this one for track days and sunny days, so the loom was effectively an ignition/charging setup plus running lights. This was helpful, because there’s a lot of heat buildup around a V4, especially when it’s boxed into a deep frame. So it was reasonably easy to keep the skinny loom away from hot exhaust pipes.

David was using stock ignition, and brought along a box of bits and pieces he’d acquired on a well known auction site. Once the loom was built I could see sparks on kickover, but a fuel hose problem meant I couldn’t start the engine. Undeterred, David picked up the bike, sorted the fuel hoses… and found the bike wouldn’t run more than a few revs. The suspect was the CDI unit, or failing that the source or pickup coils. As he had a known good CDI unit on his other bike, David drove up from Essex and I made up an adapter that would plug the good CDI into his custom loom.

Voila! The motor fired up, and sounded fit as a butcher’s dog. As you would expect from a Stan Stephens rebuild.

Anyone else experiencing weak or erratic performance from an old two-stroke needs to look at the ‘Trouble shooting CDI’ articles on the Rex’s Speedshop website. They are the best information on old CDIs anyone has produced. Actually, everything Marcus has put up there I (and there’s a lot) is really good.