US Marine 90HP Force outboard

Hello, we have just bought a 1990 Bayliner 1800 Capri that has a 90hp Force/must be older because it is still a US Marine, outboard... The guy had it hooked up to muffs and the motor sounded good when I bought it, took it out on the water for the first time this past Saturday and Sunday, and I am the slowest boat on the water..... Definitely an issue here.... The boat will start up right directly after 3-4 primes and 1 choke on the 1st start, it idles great in neutral but does not get high RPM'S.... when I shift from Neutral into gear, it wants to die unless I throttle a little hard... When we first came out of the NO WAKE zone, I wanted to open it up for the first time, I hammered the throttle forward and we hit a whopping 2500 RPM's and we never got over 2700 RPM's, it also seems to get better throttle in reverse, I am getting passed by heavy boats with smaller motors, I am mixing 50:1, I have not checked spark or compression, but I did pull each plug wire while underway and lost power on each cylinder(3 cylinder)... Although my wife is content with the 90hp "trolling" motor, I think her, my son and I all agree it would be nice to have this boat running at full potential... Any help would be greatly appreciated... Thank you! ~Mike

Re: US Marine 90HP Force outboard

Gotta do a compression test.
Check the plugs for correct burn or water.
Check fuel for water.
RPM's in water in gear?750-800.

Re: US Marine 90HP Force outboard

Thanks Jerry, going to do a compression test today, check the spark plugs, clean the carbs... etc... Also thinking about changing the prop, because the one on there is not in perfect shape but the guy I bought it off of gave me a newly refurbished one... Hoping to make some head way today to get the family out on the water at full potential

Re: US Marine 90HP Force outboard

In addition to Jerry's recommendations, it would be time well spent verifying the throttle and timing rigging- refer to Frank A's post on "linc & sync" at the top of this forum.

Re: US Marine 90HP Force outboard

Thank you Stubtail... I pulled the #1 cylinders spark plug today to head to get a compression tool and it was covered in fuel/oil.... Concerns?

Re: US Marine 90HP Force outboard

new symptom, the auto stores were out of the compression tool... I came home and decided I was going to adjust each carb and see if we gained anything, I hooked the muffs up, turned the motor over, hit 3000 RPM'S in neutral, put in gear and was able to hit atleast 6000 RPM's, backed off of course.... Is there maybe a propulison issue when it is actually pushing water, it can only reach 2500 RPM's??? Or did I possibly break something free??? We are going to go out "cruisin" this afternoon, because it is much to nice to be stuck on land working on the motor... will get back to the grind of figuring it out tomorrow... but any ideas would be greatly appreciated

Re: US Marine 90HP Force outboard

In regard to fuel/oil on plugs - you know that fuel was getting to where it needs to be, probably mixture is a bit rich, but you already know the engine is not performing to potential. Not much a concern at this point. Running in gear with no load - that raises some concern! When you attained "at least 6000 rpm", hope there were no loud noises. You may have dodged a bullet this time. Never a good idea to run in gear no load - especially to WOT. In my estimation, the higher RPM's on muffs is strictly due to the no-load situation. Drop her into the lake and let us know what does, or doesn't happen.

Re: US Marine 90HP Force outboard

Well we had her out this afternoon and after putting the refurbished prop on, we got a little better response, actually ran up to 3600 RPM's but still only hit about 12-14 knots.... Ran a good bit of fuel tho, going to try filling up with some high grade tomorrow instead of 87... If it doesnt go well, the diagnosis will continue.

Re: US Marine 90HP Force outboard

Please do not pull plug wires while the engine is running-- In addition to possibly shocking yourself, you run the risk of destroying the CD box(es).

Do not waste money on high test or high octane fuel. The engine was designed to run on 87 octane.

Since it only takes a couple of horsepower to run the engine in neutral or under no load It is easy to rev up to 6000 RPM. Even an engine running on 2 cylinders can do it.

Do not adjust carbs without knowing exactly what you are doing. Too lean a mixture WILL damage the engine.

The BEST you can do is to first check compression ratio and then synchronize timing and carb opening as per the sticky. Then, if things don't improve, check the ignition and fuel delivery systems.

2500 RPM under full throttle is only half the rated speed. Check that the engine is not trimmed in too far and the boat is not waterlogged. Also check the load in the boat. A heavy boat "plowing " bow down will obviously be slow. If she has a hydro-foil attached to the cavitation plate, try running without it. Some can knock a significant amount of speed off the top end.

Re: US Marine 90HP Force outboard

sounds like your power problems were the same as mine had its a 1987 125 force (us marine) it ran real good up to about 2500 then no more power i did a comp check top two were 140 bottom two were 40-it was the head gasket but it also was leaking drops of water inbetween 3and 4 cylender i didnt fix it my self but the guy who did said it could have been from running to high octane fuel -and i did but not anymore-live and learn.