1990 115hp

[mhope01]

I just bought a 1990 115hp for my 17ft proline. I have been reading how this is a 2+2 motor. Is there any way to bypass this? If not where do my idle and WOT rpm's need to be and when do the other 2 cylinders kick in?

 

[WillyBWright]

Re: 1990 115hp

No there is no way to bypass it. Merc did it because they idled horribly, worse than the 90 triples do which are the worst idlers ever built by anybody, ever.

WOT is 5250, idle is 750ish in gear and in the water. The bottom two carbs kick in between 1800-2400rpm, or about 1/4 throttle. In that range, they can't decide whether to run on 2, 3, or 4 cylinders.

If you can avoid that RPM range, you'll like it. But without exception, every owner that hears this "just Has" to run exactly in that range no matter what. They are awful for pontoons, and wakeboarders and beginning waterskiers because that's a pretty common RPM range for those.

The reason Merc chose this specific RPM range is that that's about where you are plowing horibly through the water making tidal waves, just below planing speed. For the most part, people either idle around or pop the boat up on plane. In those ranges, they're fine.

 

[MercGuy]

Re: 1990 115hp

I have 1998 115 and I'm very pleased with it, but it does require some special consideration. I suspect that Merc cut out the bottom to cylinders at low speeds to reduce fuel consumption. This is accomplished by simply eliminating the low speed jet from the carb. A very simple, trouble free way to accomplish the goal.

A couple things to make it run best are:

1) Assure that it's in generally good tune, with fresh plugs.

2) If in doubt do a "link N sync" to assure that timing & carbs are setup properly.

3) This is most important: prop the engine to run at MAXIMUM recommended RPM at WOT. These engines cannot be lugged. Mine bogged badly through the transition point with the 21P prop that came with it. I was stunned at how much better it ran when I dropped to a 19P.

4) Be aware that there is an external acceleration pump that squirts some gas in the lower 2 carbs to help them light up. A quick move of the throttle will generally help the engine past the transition point better than a slow movement throught the same range.

I've got over 750 hours on mine and I've never had to do any repair work to it. Seems to be a solid engine to me.

-Steve