1982 Yamaha Maxim XJ550


I have been interested in fuel injection for a long time and was mystified by the mythos of this black magic when I was in high school. I had always assumed that it was beyond mere mortals.

As years went by and I’ve gotten into robotics and other motion control applications, I began to realize that, fundamentally, EFI is not really so scary afterall. It’s not trivial, but it’s not scary.

As luck would have it, I bought an ’82 XJ550 Maxim in November 2007. It is in pretty good shape beyond the usual and expected 26-year-old-bike issues.

The only problem is that it’s a little cold natured, as the entire XJ line tends to be. In my case, it doesn’t have to be very cold before it will just crank and crank and not start. I was researching cold starting problems and found where someone had MegaSquirted their XJ1100. While it’s probably overkill for just the cold starting problem, I am so ready to do it for tinkering sake!

I also found solutions that have transformed the “impossible to start when it’s cold” issues into “grumpy about starting when it’s cold but it will do it”.

Even so, I have been shopping and the first part has arrived, throttle bodies.

I found a set of Keihin throttle bodies from a 2003 Kawasaki ZX636R on eBay and got them for the opening bid plus shipping, $45. They are spotless. The only gasoline smell detectable is by sticking the fuel rail connection in my nose and sniffing. :)

The first issue I know of right away, and I predicted this one during my research, is that the throttle bodies are all evenly spaced with the throttle cable eccentric on one end, but the XJ550 carburetors have the throttle cable in the center and the two center carbs are slightly farther apart. I don’t know at this writing if the intake flanges on the cylinder head are spaced evenly or to match the carbs.

The Keihins are really made from two castings with two TBs each, bolted together in the center. The link between the two TBs is spring loaded and adjustable for synchronization purposes, but this link may tolerate some small degree of lateral reconfiguration. Hopefully, the fuel rail will likewise be forgiving. If so, I’ll bet I can come very close to getting these TBs on the XJ without irreversibly modifying the intake tract. I would like to keep the bike as stock as possible for restoring the carburetors should the need arise.

More as it develops….