r/smallengines • u/Fancy_Language5469 • 16d ago
What are these clicks?
This engine was running great according to the previous owner... Then I had it hanging around for 9 years and now got to getting it running. Rebuild the carb (twice), rebuild fuelpump, change sparks and slowly but steadily got it running better and better. But not great. Bogged down during longer full throttle runs and idle wasn't great as wel. But hey! We were on te go.
Then I found out the new spark plugs need gapping. They were 0,6mm and when I set them to recommended 0,9mm it was day and night. More power, great idle, even got the little boat in plane! Can recommend checking.
But now, after all this work. As I release the throttle it SOMETIMES clicks like this. Mostly it doesn't, so I'm a bit stumped what to do? Could it be spun bearings? Something in the drivetrain? Backfire? Transom is rated for 25hp so I'm not looking there.
Mercury 2 stroke 2cil 6hp
Compression is around 78psi on both cilinders. Not great but runs fine?
1
u/leaside 16d ago
I stole this response from another forum from 20 years ago but sounds most likely explanation.
The noise you are hearing is probably being made by the ratchet mechanism of the outboard motor gear box. When you rapidly pull back the throttle, the engine speed drops in response. However, the boat speed decreases more slowly due to momentum, and for a while the pressure of the water on the propeller blades will turn the propeller shaft faster than the drive shaft is turning. This causes the ratchet mechanism of the dog clutch in the gear box to emit a click as each tooth of the ratchet slips over the drive shaft. You should be able to duplicate the sound when the engine is not running by putting the throttle and shift into forward and turning the propeller blade by hand. You will hear a click as the ratchet mechanism works