Last week, my father, sister, and I were at the 2011 APBA Stock-Mod-J Outboard Nationals in Wakefield, Michigan. Racing began on August 2, so we had July 31 and August 1 to get some engine testing in. My sister and I both run 200cc Modified Hydroplane, which is virtually identical to the A Stock Hydro class. Therefore, our engines are identical.
This simplified things a great deal when we were trying to troubleshoot an issue my motor was having. We were able to swap out parts and try to find the problem. The TinyTach attached to my motor was only reading about half the RPMs it should have. A healthy A motor turns at about 7,200 RPM. The tachometer read only 3,380 RPM.
This TinyTach works by wrapping a wire around a spark plug wire so that, when the plug fires, a current is created in the wire through induction. We went through a process of elimination and changed out parts with ones from my sister’s motor, one-by-one. Eventually, we found a spark plug wire with about 1 ohm of resistance when they are supposed to have about a tenth as much resistance.
It was not a huge issue, but it did show me how useful it is to have two drivers with similar or identical motors because it lets you compare the two and find issues more quickly than you might if you just tried changing things at random. When my dad was still racing, he kept a spare Yamato 80 powerhead a box of Yamato parts, which came in handy when he had to troubleshoot his 350 Mod Hydro.