90 hp Merc. problems, frustrated!

[nbf6165]

1995 90hp Mercury 3 Cylinder.<br />Have owned boat for 6 months. Boat sat in storage for approx. 3 years. Fuel was immediately emptied and new added. When on the water right after purchase the the engine would start fine, idle rough, and occasionally bog down near WOT. I changed props, installed new plugs and fuel filter. Problem seemed to be fixed, boat ran fine for couple of months. At WOT, 5500 rpm 52mph. Now problem has reoccured, but more severe. Cranks fine, idles very rough (motor kicks and knocks), bogs immediately, rarely gets on plane, catches up every so often and surges forward. I have very recently done the following: removed all 3 carbs and cleaned thoroughly, reinstalled with new gaskets, replaced most all of the fuel hoses/lines, new plugs. Same problem, maybe worse. Could be carb link & synch, but there has to be more to it. Any suggestions? Sorry so long.

 

[dolluper]

Re: 90 hp Merc. problems, frustrated!

Did you look at your fuel pump Diapharm for pin holes and a link and sync will make a big difference Howdy to IBOATS edit : hows the pee'er doing good steady stream coming out if not tou might want to change impeller [waterpump]

 

[KCLOST]

Re: 90 hp Merc. problems, frustrated!

Did you check spark at idle? And is there a fuel/water seperator on the fuel line, check it?<br /><br />This could be electrical, since it came on so suddenly after running just fine...

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

Is link & synch a difficult task? I'm hoping to do as much as possible myself. Pee hole is just fine, strong flow. There is no fuel/water sep., just an inline filter. I'm certainly no mechanic but I did pull plugs while at idle using water hose. #1 had little spark, #2 almost electricuted me, didn't mess with #3. After reading many threads, I wonder if my prob. could be in fuel pump diaphragm as stated by dolluper, the stator, switch box or rectifier. Black oil/gas on all plugs.

 

[dolluper]

Re: 90 hp Merc. problems, frustrated!

I think right about now is a good time to buy a manual as it would give you step by step instructions on your specific motor like how to link and sync 'read plug spark ,test coils ,switch boxes ,stators ,triggers since you are willing and get back with any problems you have testing

 

[KCLOST]

Re: 90 hp Merc. problems, frustrated!

Don't pull the plugs to check spark, LOL<br /><br />Use a spark gap tester... $10 at any auto parts store...

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

I have purchased seloc online manual but am a little disappointed with the repair section. I didn't actually pull out the spark plug just pulled the lead off.

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

but this sounds electrical to you guys? not fuel/carb related

 

[phatmanmike]

Re: 90 hp Merc. problems, frustrated!

i have the same motor but mine is 1990. that rough idle you speak of is actually how the beasts were designed. thats a major complaint about these things is that they have a CRAPPY idle, almost like it wants to stall...<br /><br />i agree with the fuel pump scenario, check that, its definately cheap enough to try. also, check that the timing is propper, both at wot and idle.<br /><br />hows you compression. maybe you could use a REAL GOOD decarb. i had a merc 115 that would run just like yours and i rebuilt the fuel pump and decarbed the **** outa it and then it ran great. what a difference, lots of goo came out.<br /><br />when you say that you "took apart and cleaned the carbs" how indepth did you get. if these jets are the SLIGHTEST bit dirty, it will perform bad.<br /><br />by the way, are you using the oil injection still? or premixing it..... i use my injection<br /><br />just a few thoughts

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

I took the carbs off and apart removed every screw, float, etc and they are spotless. #1 & 2 weren't very dirty, 3 however was. It is oil injection.

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

The vibration in this motor is terrible. Even more so at very low speed. Thanks for any responses, you guys are a lot of help.

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

Compression tested as follows: 135, 130, 130

 

[shipoffools]

Re: 90 hp Merc. problems, frustrated!

I have a 1988 70 hp same basic configuration same situation sat for a couple years before I got it.<br /> The "Clymer" manual is pretty good. Most of the previous posters have covered the possible problems, I have replaced switchbox, 2 coils, just about every hose and anyhing else made of rubber or plastic that flexes. The fuel pump gave me fits, for about $15 and 15 min labor it's well worth replacing. Also you might want to replace the impeller mine self destructed at about 5 hrs. A little time and $$$ cleaning it up and you have a pretty stout engine it will vibrat at idle but should give you lots of power and judging by how many Mercury 3 cyls I see around they must last awhile<br /><br />Good Luck

 

[WillyBWright]

Re: 90 hp Merc. problems, frustrated!

Merc adopted a strange method for smoothing the idle, but I don't like it. They lean-out the idle mixture screw on the top carb to allow enough gas to enter and carry the oil along, but not enough to fire. It's as simple as the #1 carb idle screw at about 1/2 turn, the other two at about 1 to 1 1/4. Problem with that theory is that they bog badly at acceleration. They can be tweaked to do better, but it seems to be a constant battle depending on weather conditions, etc. Adjust all of them the same. (Without the factory manual, you were probably unaware of this and I doubt you'd have done it Mercury's way).

 

[nbf6165]

Re: 90 hp Merc. problems, frustrated!

ok, I've replaced the fuel pump diaphragm kit. Old diaphragm was a mess. I decarbed. Compression was 135,130,130. Took boat out today and it still bogs. However, it must not be getting fuel. When I pump the bulb while sputtering along at a very slow speed, it takes off and hauls tail until it burns that small amount of fuel. What next?

 

[jimalsk]

Re: 90 hp Merc. problems, frustrated!

Is the vent open and clear?? Just a thought

 

[phatmanmike]

Re: 90 hp Merc. problems, frustrated!

my merc 115 inline did this same thing. turned out the fuel line and fittings were too msall, so i got bigger line, 3/8, and all is well

 

[mellowyellow]

Re: 90 hp Merc. problems, frustrated!

fuel starvation. start with a new fuel source<br />like a portable gas can, then work backwards<br />towards the motor.<br />primer bulb has bad check valve<br />quick-connect isn't tight and it sucks air<br />cracked fuel line or fitting lets air in<br /><br />then I would look at the floats and needle valve/<br />seats. could be a stuck float or even bad check<br />valves in the pump.

 

[fishkisser99]

Re: 90 hp Merc. problems, frustrated!

hey nbf--was this ever resolved?

 

[andy6374]

Re: 90 hp Merc. problems, frustrated!

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