90 HP Mercury Outboard with BAD Problems

[bassin_baloo]

Hello,<br />PLEASE HELP!<br />I have a 1987 (I think) 90 HP Mercury six cylinder Outboard on a 16 foot fiberglass boat. This rig is new to me as of December 2001. I have experienced the following problems:<br /><br />First, the motor was a bear to start 2-3 minutes of turning the key.<br /><br />Second, the motor would run about 23 mph for the first 15-20 minutes then without me doing anything, kick in and accelerate to 35 mph. After this the motor was fine for the rest of the day.<br /><br />Third, I talked with a local boat mechanic and he said that my problem was bad and that I needed to get it fixed before major problems occurred. I left the boat with him and he made the following repairs: 1) Replaced the trigger assembly 2)changed all spark plugs 3) rebuilt all three carbs 4) replaced one of the switch boxes 5) tested the stator and all readings were within specs 6) he performed several misc. test including a drop cylinder test and some test on the water where he had a box that he could run test with the motor under a load 7) replaced the carb jets with 72,000 8) played with props to see if a difference occurred and all test with props ranging from 17-23 pitch were unsuccessful 9) replaced the fuel bulb and checked all fuel lines.<br /><br />With all these repairs, the motor is worse than before and the mechanic says he has no idea what to do. The motor now is even harder to start than before and boggs down when going from an idle to full acceleration. Top speed is now a whopping 31 mph with rpm's at 3900. <br /><br />The mechanic and myself are at a complete loss. The motor appears to run great just something holding it back! One final note, the compression is 160 on all six cylinders and all six are firing. Also, the timing has apparently been readjusted and is fine.<br /><br />Any and all suggestions are greatly appreciated!!! PLEASE HELP<br /><br />Thanks,<br />Adam

 

[12Footer]

Re: 90 HP Mercury Outboard with BAD Problems

Welcome to iboats, Adam. It sounds like the wrench has tried all the right areas. All I can add is,something was missed the first time, and must be redone. Two things not mentioned were the key and keyway in the flywheel, and the magnets.<br />These fuel pumps are tricky too, as he probably told you already. Is there any signs of fouling on any of the plugs? That would narrow the search down to the carb/cylinder/plug/pulse which is not werkin right.

 

[hondon]

Re: 90 HP Mercury Outboard with BAD Problems

Here's a little test that may or may not help you. Take a long bladed ,well insulated screwdriver and connect a jumper wire to the blade of the driver and a clean engine ground. With the engine running, pass that blade around and up and down each plug wire.Any arcing or cylinder droppage?

 

[wyattm]

Re: 90 HP Mercury Outboard with BAD Problems

Two things you might want to check is the type spark plugs - I have merc 200 v6 and with champion plugs they do not operate well at all, with ngk runs like a top. Also some mecury lower units lose a tooth on a gear and makes the engine sound like it has a blown a cylinder.

 

[Gold Bear]

Re: 90 HP Mercury Outboard with BAD Problems

bassin_baloo,<br /><br />The engine is bogging "out of the hole" because the idle circuit is lean. I have a 115 hp Merc (very similar engine) that used to do the same thing. Try this...<br /><br />1) Set all three carbs idle screws at 2 turns open from lightly closed. (I'm guessing your mechanic has it at 1-1/2 turns now.)<br /><br />2) Set the idle speed with the boat in the water, in forward gear.<br /><br />3) After setting the above adjust the throttle cable so it doesn't bind.<br /><br />First start of the day - use a squirt bottle with pre-mixed gas - and give each carb about four or five squirts (tilt the engine all the way down first). The engine should start right up for the rest of the day, after that first time.<br /><br />Buy a bottle of "Seafoam" de-carb (carbon cleaner - NAPA auto part stores carry it). Use a squirt bottle to spray about half the bottle through you carbs then put the rest of the bottle in you fuel tank.<br /><br />There are other post on this board covering de-carb details.<br /><br />I think you will see a big improvement.<br /><br />Good Luck,<br /><br />Gold Bear

 

[bassin_baloo]

Re: 90 HP Mercury Outboard with BAD Problems

Hello All,<br /><br />Thanks for the great information. I will trythese various ideas and let you all know what works. Take care and thanks again for the input!<br /><br />Adam

 

[smiley]

Re: 90 HP Mercury Outboard with BAD Problems

I suspect stator anyway. I've seen the spec out under no load and fail under running load.

 

[adison12]

Re: 90 HP Mercury Outboard with BAD Problems

For 3 years my 1997 90hp 2 stroke outboard engine loses power.I go from 38 to 25 now.Its like i lose a cylinder.It has been more frequent of late and it doesnt go away unless i leave the boat sit a while,then it'll run a couple miles then do it again.The previous 2 years this issue only happened once in a blue moon and now it is happening every time out.sound familiar anyone?

 

[hamit59]

Re: 90 HP Mercury Outboard with BAD Problems

I would look at the stator real hard.I had one drive me nuts this summer on a 115hp. I would run it on muffs nothing seemed wrong.this came in for a tune up. I took the boat for a test run it would not get to 2900 rpm then it would take off like you flipped a switch. reading on the stator were great, well in specs. After 15 to 25 min at 5000 it died like you cut the key off, I thought I had a kill circuit problem. I couldn't find anything wrong with that.but no spark at all. So I went back to the now hot stator readings were all over the place. So we loaded it up and headed to the shop. A hour long ride.
When we got there I said try to start it, it fired up like nothing was wrong.
I now have a piece art work on my office. a 115 stator that cost me a 10 total hours and 3 trips to test to find out it was bad.

As for the starting you may be too lean like was said above open up on your mix screw 1/2 -3/4 turn it should start a lot better.



I hope this helps some one don't ever trust a stator readings