Ok, question because just having something that works isn't good enough, I need to understand why...
I have gone through several tachs for my Yamaha F40 (3 cylinder, four stroke) over the years. These are inductive tachs with a wire wrapped around a spark plug wire to pick up the spark. The first couple were Yamaha branded 4 stroke tachs, they didn't last long (sealed internal battery) and were fairly expensive and were somewhat finicky to get a good reading. I had another one that worked well in the interim, but I couldn't find another of the same brand/model to replace it. So, I searched high and low and found a tach that was listed to handle 3 cylinder, four stroke motors. A 3 cylinder, four stroke motor should be a 3 spark per 2 revolution motor per the reading I've done on the internet on several boating forums and per the directions on the tach.
So, the tach does not give the right RPMs set on 3 sparks per 2 revolutions, but it does give the right RPMs on 1 spark per 1 revolution (I verified the RPMs using a laser non contact tachometer on the flywheel). Further the old Yamaha tachs I bought were just 4 stroke tachs, no reference to number of cylinders, so that jives with what I'm seeing with the 1 to 1 setting working.
Can someone who understands this stuff explain it to me in brief?
I have gone through several tachs for my Yamaha F40 (3 cylinder, four stroke) over the years. These are inductive tachs with a wire wrapped around a spark plug wire to pick up the spark. The first couple were Yamaha branded 4 stroke tachs, they didn't last long (sealed internal battery) and were fairly expensive and were somewhat finicky to get a good reading. I had another one that worked well in the interim, but I couldn't find another of the same brand/model to replace it. So, I searched high and low and found a tach that was listed to handle 3 cylinder, four stroke motors. A 3 cylinder, four stroke motor should be a 3 spark per 2 revolution motor per the reading I've done on the internet on several boating forums and per the directions on the tach.
So, the tach does not give the right RPMs set on 3 sparks per 2 revolutions, but it does give the right RPMs on 1 spark per 1 revolution (I verified the RPMs using a laser non contact tachometer on the flywheel). Further the old Yamaha tachs I bought were just 4 stroke tachs, no reference to number of cylinders, so that jives with what I'm seeing with the 1 to 1 setting working.
Can someone who understands this stuff explain it to me in brief?