1997 mariner 115 hp 2+2 question

[109jb]

Hi all. I have a 1997 Mariner 115 hp, 4 cylinder outboard on my boat. This is the 2+2 motor where the bottom two carburetors don't have idle circuits in them. The boat is used for pleasure and for fishing. For pleasure it works fine for me as the boat isn't at idle all that much and runs real strong at higher rpm's. However, when trying to troll at idle speeds for any length of time the engine wants to stumble. I have a manual and have checked everything and it seems to be in specs. My last boat had a 1974 70 hp Johnson 3 cyl and that thing would idle forever like a sewing machine and not complain. Anyone have any suggestions? Also, has anyone ever replaced the bottom carburetors with ones that do have idle circuits? If so, how did it work out?

 

[MercGuy]

Re: 1997 mariner 115 hp 2+2 question

This might be a real long shot, but I'm going to put the idea out there and see how many sharks start circling

I have a 1998 115 2+2 and recently while doing some routine inspecting I noticed signs that water was leaking out from under the bolts that hold the exhaust cover in place. I retorqued the bolts and made a mental note to get some new gaskets next time I as at the store.

The next time I took the boat out on the water I was stunned at how much better it ran. It idled better, accellerated better, and pulled strong up to WOT. I realized that the general performance of the engine had deteriated so slowly that I didn't really noticed.

My theory is that the exhaust cover gaskets went bad and in addition to leaking water they reduced the engine vaccum which resulted in poor to moderate fuel pump performance. This might be especially noticable at idle where there would be less vaccum in any event.

Like I said, it's a long shot, but food for thought in any event.

 

[109jb]

Re: 1997 mariner 115 hp 2+2 question

Hey, I'll try anything. I'll give it a look tomorrow.