motor is haunted

[twodog]

i have been reading other boaters posts and just signed in today with a problem thats making me nuts. i have a 2001 merc 90 2 stroke saltwater outboard. while cruising along at about 3000 to 4000 rpms, out of the blue, the motor will speed up a 1000 rpms for a few seconds, then go back to where i had it. ive changed the plugs, filter and added stabil to motor. please help. thanks,

 

[daveswaves]

Re: motor is haunted

i have been reading other boaters posts and just signed in today with a problem thats making me nuts. i have a 2001 merc 90 2 stroke saltwater outboard. while cruising along at about 3000 to 4000 rpms, out of the blue, the motor will speed up a 1000 rpms for a few seconds, then go back to where i had it. ive changed the plugs, filter and added stabil to motor. please help. thanks,

Welcome to I boats, is the engine running smoothly at the 3000 to 4000 rpm or does it sound a little rough? You could have a cyl misfiring and then firing, perhaps a loose plug wire or arcing to ground. The other possibility is cavitation if the motor is too high on the transom. How does it run at WOT?

 

[twodog]

Re: motor is haunted

thanks for the direction. im usually bikes and have had this boat for about a year now. i will definately check for the misfiring and im not sure what WOT means. thanks

 

[twodog]

Re: motor is haunted

ijust noticed i didnt answer a question. it does run smooth at the low speeds as well as when it decides to "run"

 

[daveswaves]

Re: motor is haunted

WOT is wide open throttle.

 

[twodog]

Re: motor is haunted

ah, WOT. yes it seems to run smooth at WOT. its on a 24' pontoon, so wide open isn't really lightning speed. you mentioned before about the spark. is it possible with this motor for it to seem smooth running on two instead of three?

 

[Faztbullet]

Re: motor is haunted

its on a 24' pontoon

Problem solved:
1) engine trimmed a little to high and prop looses bite
2) prop is loosing bite due to dings,dents and damage
3) prop has lost pitch or cup from flexing over the years

 

[twodog]

Re: motor is haunted

thank you all very much. this really sounds like you all got it figured out. let you know how it comes out. ty