merc 100hp 1989

I'm looking at an '89 100hp (oil injection, 4 carbs). Apparently, at idle and low speeds it runs on bottom 2 cylinders, then top 2 kick in when rpms go over about 1,200. The motor has low hours, good compression, new impeller and rebuilt carbs. Anything I should know about this vintage 100hp mercury? Are the oil injection, fuel pump, and electronic ignition reliable? Anything I should watch out for?

Re: merc 100hp 1989

I've got a 115hp same year, with the same set up as you describe. I've had it as the 3rd owner for about 10 years but haven't run it a ton. Nothing bad about it jumps out at me, I've done usual maintenance and winterizing as you would on any other engine. Mine may need starter work, it will spin when attempting to start on occasion before catching. Oil injection works fine, and tons of power on my Crestliner. No fuel pump issues, but I should mention that it has developed a hitch of some kind where during mid cruise, the engine will drop about 500 RPMs than rise back up. Kind of scarey, and will need to look further into that. It can be hard starting sometimes particularly on the trailer. Need to have it sitting level otherwise I think it screws up the carb floats. Oh and its a bit of a fuel hog so thats a consideration relative to newer engines. On what size boat do you plan on using it?

Re: merc 100hp 1989

Thanks for the response. I plan to put it on a 19' aluminum (Sea Nymph Great Lakes Special). I'm close to Lake Michigan so don't use the big motor much to get to the salmon (max 3 miles away), then use the trolling kicker. The 100hp may be good for trolling since it runs on 2 cylinders at low rpm. I'll see. My main concern is whether the oil pump and fuel pump are reliable. They seem to be since they have lasted this long. What size is your Crestliner and where do you use it?

Re: merc 100hp 1989

TIll now, no issues with the fuel or oil pump. Now I;m hoping that hitch in the engine was just some dirty fuel. I had it water tested by my mechanic and he couldn't duplicate the problem. That was the last time it was on the water last year, so will see shortly when I de-interize it.

My Crestliner is 17'-6" similar set up to the boat you have, dual console open bow. Great for the kids pulling tubes, and fishing etc. Getting a little small now for 5 of us on it at one time. I like to take it up to Lake George in NYS island camping. Otherwise go to the Hudson river or other local lakes. I haven't trolled with mine much so not sure how it will do on fuel, but I think I would use a 4stroke kicker if that was the case. Certainly would use less fuel, and put less hours on the main motor. Good luck with it!

Re: merc 100hp 1989

Are you happy with it running on 1/2 cylinders,or are you looking for help/ repair.I'm pretty sure it's not a feature.let me know cause this was happening on my 1988 135 v6 merc and it wasn't a cheap fix.Both switch boxes and Trigger replaced.

Re: merc 100hp 1989

Sorry,forget my last post,it is a feature.You have a 2+2.Wish my V6 could do that.