90Hp Merc Problems 2024

NHfroggin reply :

I have a 77' mercury 90 hp, last year i felt a big power loss the last couple times i went out. It wouldnt get up on plane as fast and i lost about 10mph. This year it wont even start without giving it throttle then stalls when i try and go to idle or put it in gear. i was able to get it into gear a couple times and it only reved till 1800 rmp's and i was only at 6mph. That was at 3/4 throttle any more throttle and it would stall. It will rev normally in neutral. Im not sure wich direction i should be headed any tips would be greatly appreciated. If you need anymore information just ask!

Thanks

-Matt-

Nice_Bass reply :

Does it sound like it is running on all cylinders?

Fishing Rhino reply :

Apparently you were aware that the motor had problems, or was beginning to have problems at the end of last year. With that in mind, did you winterize the motor when you were done fishing?

Are you trying to run it on the fuel left in the tank from last year? Is it possible that your loss of speed could have been the result of old fuel?

If you didn't treat the fuel or winterize the engine it could all be fuel related. The carbs could be a mess because fuel with ethanol can contain water which will accumulate in, and gunk up carburetors. They may need a thorough cleaning by someone who knows what they are doing.

If you don't treat your fuel when you fill up or add fuel, it's something you should do. The "shelf life" of fuel with ethanol isn't very long. From what I've been told it can go bad in as little as three months.

NHfroggin reply :

@nice_bass im not sure what it would sound like if it wasnt running on all cylinders but it seems to be fine, thanks for the reply.

@ fishing Rhino i was aware of the problems last year however i didnt have the funds to have it looked at. There was about a gallon of gas from last season and i added six gallons of gas before i went out. If by treat your fuel your referring to a seafoam type additive i always include it in my fill ups. I did not run the motor completley out of fuel last season because i read that it was not good for the engine? this may not be correct. I am no expert on motors so im sorry if im not 100% clear. Would you begin with cleaning the carbs? Thanks for the reply

-matt-

GLADES reply :

Make sure all your plug wires are secure and your gas is fresh. With a motor that old it could be anything from fouled plugs and old wires to electrical problems in addition to fuel pump and carb issues. You may have to get the compression and spark checked to help diagnose the trouble..

bass crazy reply :

Since your motor is a 1977 model check your fuel lines / fuel pump diaphram /carb gaskets. They might be deteriated from the ethonal fuels we have now and need replacement.

Bassn Blvd reply :

It's a 35 year old motor. How will do run after 35 yrs?, lol.

Sorry I have nothing to offer other than sarcasim.

NHfroggin reply :

Thanks guys, i took it out today and had someone squeeze the primer bulb to act as the fuel pump and there was no difference. I was also told to hit the choke while its running to see if that helps although i didnt try it yet. I talked to the marina and they said the carbs probably need to be cleaned(450$). Looking at the SELOC repair manual it looks like an extensive job, has anyone done this themselves? or do you recomend having the mechanics do it?

thanks for the help

-matt-

Nice_Bass reply :

I would not take a "carbs probably need cleaned" and hope for the best at $450...but I would let a mech. do it if you are unsure. Could be as simple as plugs. Did they hook it up to the hose and look at a variety of simple solutions?

GLADES reply :

I would look for another mechanic and get another opinion on what is wrong. Just describe the problem and do not give him your theories. He will sell you a carb rebuild if you suggest it. The problem might be electrical or mechanical too. The price quoted for the carbs rebuild is high IMHO.

Just my .02 Good luck.

Nitrofreak reply :

If you choked the engine and there was no change at all, it's not the carbs, it sounds like it is down on cylinders, like a power pack has faulted.

How mechanically inclined are you?

Way2slow reply :

First thing you need to do is determine if it's ignition, fuel or compression. After doing a compresison test that shows all cylinders good, having sat that long, the first thing I usually do is pull the carbs and clean them, BUT! it doesn't cost me $450, most of the time just a few hours of my time. Before forking out $450 for a carb cleaning, I would like to know for sure there's not something with the ignition system causing my problem. I would hook a spark checker to it, and make sure it's firing on all cylinders while cranking it over. If that's good, I would take it to the lake, leave it strapped to the trailer, back it in until the anticav plate is about an inch above the water, have someone put it in gear and momentarily apply power while I took a plug wire off and see if that made a difference, I would do this for each cylinder, but do not keep the power applied while you try to check all of them, have the wires loose so they come off easy, pop it off and see if motor changes, let off the gas, shut it off, put that wire back on, start it back up and try another. If you don't mind getting your eyeballs lit up, you can try to putting it back on while it's idleing. Then you need to make sure the motor is firing on any cylinders that don't change when you pop the wire off by using a spark checker and do the same run up, but not take the wire off.

Now, if I'm not over your head on troubleshooting your problem and you do try this, do not do this standing in the water behind the boat, sit on the back and reach over or around. For one, several thousand volts is going to hurt like h*** if you are standing in the water and two, that prop is moving a hellavalot of water and can easily suck a foot/leg into it.

One novel thought, have you even looked that the plugs to see what they look like, if you are running the gapless plugs those motors normally run, they foul pretty easy and it would would make you feel kinda stupid it you spend hours and bunches of money just to find out the plugs are fouled.

slonezp reply :

On 5/22/2012 at 11:13 AM, Bassn Blvd said:

It's a 35 year old motor. How will do run after 35 yrs?, lol.

Sorry I have nothing to offer other than sarcasim.

If you're going to be sarcastic, you could at least spell your words properly

Crookedneck reply :

It could be carbs, but, it could also be a head gasket problem too. I had an older evinrude start acting up on me last year. It started fine, idled fine. No guts to it. After a compression check which turned out ok. It turned out that the head gasket was bad. I was loosing compression due to gaps in the gasket. In saying that, very rarely does a gasket go bad. Just what happened on my motor.

Good luck.

NHfroggin reply :

-Hey guys sorry i never responded, a college graduation, deaths in the family, and a couple 80 hour weeks will put the motor lower on the priority list.

-I ended up bringing the motor to the shop and there were a list of problems including bad compression and the carbs needed to be cleaned. It was going to be close to $1000 for all the fixes. I ended up buying a 1988 mercury 90hp off a guy i work with for $600. The only problem was it did not have power tilt/trim. We decided to take the power head off my motor and replace it with the newer. Everything went well except now when the propeller is rotated clockwise it clicks 5-6 times per rotation. im not sure if we did something wrong but my guess would be the shaft is misaligned or something? any input would be greatly appreciated!

thanks

-matt-

Fishing Rhino reply :

I'm assuming it's in neutral, or supposed to be, when you are turning the propeller. If that's the case, it sounds like the "dogs" on the "slider" (sorry, don't know the actual name) which engages the forward or reverse gears is not fully disengaged. There are probably five or six teeth that engage the gearcase. That's why you are hearing the five or six clicks per rotation.

Try moving the control lever slightly toward the forward and reverse positions while someone is turning the prop. If it gets into a position where the clicking stops, you'll need to adjust the shifter cable. Don't know why changing the powerhead should affect the shifting adjustment. It's just a guess off the top of my head.

There are many with more expertise than me on the forum, but it will give you something to try 'til you get a better reply.

GLADES reply :

On 7/2/2012 at 7:16 AM, NHfroggin said:

-Hey guys sorry i never responded, a college graduation, deaths in the family, and a couple 80 hour weeks will put the motor lower on the priority list.

-I ended up bringing the motor to the shop and there were a list of problems including bad compression and the carbs needed to be cleaned. It was going to be close to $1000 for all the fixes. I ended up buying a 1988 mercury 90hp off a guy i work with for $600. The only problem was it did not have power tilt/trim. We decided to take the power head off my motor and replace it with the newer. Everything went well except now when the propeller is rotated clockwise it clicks 5-6 times per rotation. im not sure if we did something wrong but my guess would be the shaft is misaligned or something? any input would be greatly appreciated!

thanks

-matt-

It sounds like the F-N-R shift cable is not properly adjusted..but I am no outboard mechanic.

Gotfishyfingers? reply :

I'm assuming your hearing these clicks with the motor turned off and out off the water. The clicks your hearing means the throttle lever is in gear. Make sure the lever is in the neutral position. The clicks should go away. The noise SHOULD be normal IF the boat is in gear. Props make that same noise as your moving and you turn the boat off while it's in gear. try that first.

NHfroggin reply :

thanks for the quick replies

@fishingrhino i will try that tomorrow.

@gotfishyfingers it is when the motor is out of the water. It doesnt sound like the normal clicks its very loud and distinct. I found this youtube video and this is exactly what it sounds like.

Also the throttle cables are the only things not connected right now, im not exactly sure how to attach them to the motor.

thanks

-matt-

Gotfishyfingers? reply :

YES that is it. Your engine is in gear. if it was in neutral the sound should go away. It's normal, notice in your video as soon as the engine starts, the prop is engaged. If it was in neutral and you spin the prop there will be no noise.

NHfroggin reply :

I was having trouble getting it in neutral so i brought it to the shop. They did a compression check on it before they re-installed the lower unit and cylinder three was bad, compression was at 105. im glad i didn't pay for the motor yet, and i guess its back to searching for a new motor.

Thanks for all the help

-matt

Gotfishyfingers? reply :

Can the cylinder be bored out and a new piston and rings put in? I'm sure you can find the parts online.

Also check craigslist in your area for a used engine, you never know what you will find there.

Maxximus Redneckus reply :

Sea Foam it.... this stuff is amazing

Long Mike reply :

I have serious doubts that a fuel additive would improve the compression ratio. I know that my favorite, Star-Tron, removes the ethanol gunk in the engine intakes, but I doubt the it would be effective at improving engine compression.

NHfroggin. You made the right decision. Walk away from that motor.

NHfroggin reply :

-Thanks for the help guys. Im not going to try and fix the motor because i would have to pay for the motor and then get it fixed, if its possible. Right now im looking into motors on craigslist. Im definitely going to buy a compression tester to bring when i go look at them.

-What do you guys think about a new motor, should i stay at 90hp go higher to a 100-115? or go lower and find a newer 70hp?

-the boat (15' 5" Cajun) with the 90hp would go 45mph with two people and a full load.

Any input would be great,

Thanks

cwb60 reply :

Check the oil in the lower unit. If you have a bad seal and it is letting water in it will start bindiing up and your engine will not rev up when it is in gear. If oil is milky looking, drain it and check for metal filings.

That is a long shot, but it won't take long or cost much and needs doing anyway.

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90Hp Merc Problems 2024

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