Mariner 60hp mid range power loss

[Fisherman Eddy]

Hi All,
this is my first post - I must say that this is an excellent site!.
I have a problem with my 1989 60hp Mariner/Mercury which I could really do with some expert help. I use the engine at sea on the back of a 17ft Broom speedboat.

The problem is that above 8kts, just as the high speed coil engages the engine bogs down and stalls. If I push the throttle fully forward quickly from low revs the engine responds and runs at WOT without an issue until I throttle back to medium speed then it bogs and stalls. I am hoping that someone will recognise this strange behaviour - low speed ok, medium speed stalls, high speed ok.

Within the last 2 years the engine has had a new high/low speed coil & new switch box fitted, I have replaced the plugs with no change in behaviour.
Does this sound like a timing issue?.
Any help would be gratefully received.

Kind Regards

Eddy

 

[Fisherman Eddy]

Re: Mariner 60hp mid range power loss

checked the choke - not sticking, please help!.

 

[al9981]

Re: Mariner 60hp mid range power loss

I am having the same problem with my 1986 75hp Mariner (2 stroke). But this problem doesn't happen all the time. It happened yesterday after I gave another boat a pull to the shore. And sometimes it happens when I am pulling a tube. I rebuilt the carbs and new spark plugs. But I noticed that when it starts to happen, the engine runs rough in idle. So I pushed the choke few times and the engine revs up and the roughness went away. I am not sure if that means it didnt have enough fuel or air leak in the gas? not sure how to test for that!!!