2001 40 hp mercury

[Matthew Landreneau]

Hi everyone i have a 2001 mercury three cylinder outboard, last year i had the motor professionally rebuilt, and the mechanic converted the engine to a 60 hp by changing the carbs and removing the reed stoppers, the problem I'm incurring is the engine will not run over 4200 rpm's i disassembled the carbs and cleaned them out changed the plugs and went test drive the boat. upon launching the boat i immediately accelerated to full throttle and the but revved up and ran better than it had ever ran before but after only about one month I'm back to only running at 4200 rpm's at WOT, any suggestion? Also prior to any of these problems i noticed a rattle sound that comes from the engine when running at WOT and immediately slowing to an idle any thoughts on that?

 

[joe5701]

as for the revs i'm not sure (maybe ignition timing) dont know why it would be up and down though, the rattle sound when backing off will most likley be coming from the gearbox. when out of the water not running put your motor in forward gear and try to spin the prop both ways, one way it will lock the other way it will slip making a clicking sound. when you slow down the water pressure spins the prop faster than the meshing gear does and it clicks like mad. thats my opinion hope it helps.

 

[fastjeff]

Oooooouuugghhh! The poor thing is pinging its butt off 'cause the carbs are jetted too lean. It may be too late to save it, but you need to do a plug check ASAP.

Since that motor has surface gap plugs (I assume) you'll need to put conventional ones in there for your test. (I recommend Autolite # 303s.) Warm the motor fully, then run it at WOT for at least 30 seconds before slowing down as fast as you dare and shutting it off. Next comes pulling and reading the plugs. And it they come out stark white, that tells you the motor is running dead lean.

Jeff

PS: A "professional" mechanic should have done the above right away after such radical modifications.