1975 135HP Johnson
Last night, I found out I had a bad rectifier. There was no voltage change between engine off and a high idle as read across the battery. I ran through the rectifier test procedure comparing forward and reverse voltage passing over each diode (Y-Gnd, Y/G-Gnd, Y-Red, Y/G-Red) and got infinite resistance over each combination except one (Y/G-Gnd or Gnd to Y/G, I don't recall which direction).
So I replaced the rectifier and started the engine. it ran rough so I thought now I may have to redo my fine tuning now that the new rectifier was in. Then I noticed my tach was running at a higher number. Instead of showing about 650-700 rpm it was now showing about 1200. But it didn't sound like it was revving much higher than before the new rectifier, to my very untrained ear.
I can assume that maybe now the tach is seeing twice as many pulses now that the rectifier is working correctly (aledgedly) an possibly my earlier tach readings were wrong due to the bad rectifier. All I know is that if I lower the rpms down to less than 1100 the motor just dies. So perhaps the reason my engine was working fine at low idle was because it wasn't really at low idle. Would it be obvious when shifting with an idle at 1200 that the idle was too high? I didn't notice a big clunk or other evidence of a hard shift.
Last night, I found out I had a bad rectifier. There was no voltage change between engine off and a high idle as read across the battery. I ran through the rectifier test procedure comparing forward and reverse voltage passing over each diode (Y-Gnd, Y/G-Gnd, Y-Red, Y/G-Red) and got infinite resistance over each combination except one (Y/G-Gnd or Gnd to Y/G, I don't recall which direction).
So I replaced the rectifier and started the engine. it ran rough so I thought now I may have to redo my fine tuning now that the new rectifier was in. Then I noticed my tach was running at a higher number. Instead of showing about 650-700 rpm it was now showing about 1200. But it didn't sound like it was revving much higher than before the new rectifier, to my very untrained ear.
I can assume that maybe now the tach is seeing twice as many pulses now that the rectifier is working correctly (aledgedly) an possibly my earlier tach readings were wrong due to the bad rectifier. All I know is that if I lower the rpms down to less than 1100 the motor just dies. So perhaps the reason my engine was working fine at low idle was because it wasn't really at low idle. Would it be obvious when shifting with an idle at 1200 that the idle was too high? I didn't notice a big clunk or other evidence of a hard shift.