90HP merc problems

[photoguy66]

I have a 1984 90hp merc inline 6, and am having some problems with it. I winterized it, took it out for the first time this year and it ran great, the second time I took it out, it started and idled fine, got it on plane at about 2000 rpm's (17ft aquasport cc)then the motor started bogging down and "pulsing",meaning revving normally then bogging down repeatedly, then I backed off the rpms and it would still run rough.brought it back to dock, idled it, noticed alot of dirty looking stuff coming out of the exhaust, figured it was stale gas, hooked up 5 gallon tank with fresh fuel/oil mix, no change.took out plugs which are brand new, all were very clean except #3 and #5 which were slightly dirty. Found one cracked fuel line which I replaced,took off float covers, cleaned bowls, sprayed with cleaner, started it back up, idled great, took it out 2000 rpm's, same scenario happened again, ran rough with lots of pulsing but idled fine and at low speeds, it ran fine and I got it up on plane but it only lasted for a bout a minute before the bogging and the pulsing started again.If there are cracks in the fuel lines would this be indicative of the problem? or does it sound more like a carburator problem,or maybe something else?Thanks Rick

 

[photoguy66]

Re: 90HP merc problems

I forgot to add, I had the EXACT same problem last year when I took it out for the first time but it fixed itself. I used a gas stabilizer in the tank for winter storage, could my fuel have gummed up and caused some carbuerator blockage?

 

[Clams Canino]

Re: 90HP merc problems

Sounds more like a primary fuel delivery problem. Have a helper pump the ball at speed and report back.<br /><br />-W

 

[photoguy66]

Re: 90HP merc problems

Clams, I did try that, had my father pump the bulb with no effect.Would air being sucked into the fuel lines cause this to happen? Can't figure out why it runs great for about a minute, then like crap

 

[photoguy66]

Re: 90HP merc problems

bump

 

[LazyJ]

Re: 90HP merc problems

If said fuel hose you replaced is aft of the filter then it has likely dumped a sprinkling of little rubber flecks into your carbs

 

[Laddies]

Re: 90HP merc problems

Get some carb and injecter cleaner double mix the amt. called for in your fuel and run it on the hose for 1/2 hr, let it set at least over night and try to run it again hopefully that will clean it out. I have never had any luck with stabilzer of any brand, the best thing to do is run the systems dry, I've done it that way for 45 years and have less problems that way than anyother way. This should start a discussion but it works for me---Bob

 

[Clams Canino]

Re: 90HP merc problems

Also... since there's a 2000 RPM wall, he might do well to have the stator ohmed out / tested.<br /><br />The high speed windings might be shot. Disregard this if you can See 4000 on plane - even for 10 seconds.<br /><br />-W

 

[mickjetblue]

Re: 90HP merc problems

I have had an '83 for a couple of years, and it runs great.
The only time it ran a bit rough and "guzzled" gas was when
I was using gas that the oil company just started to put ethanol
in. I switched to a cheaper gas station that uses 100% gas,
although I use plus, and not regular. I don't think the '80s engines
do well with ethanol mixed into the gas. It likes 100% gas with no ethanol.

I also use a carb/injector cleaner additive occasionally.
I like cruising occasionally at about 5500rpm. At that rpm range,
the engine hums like it's happy and doing what it wants to do.
I'm holding on to it, because of that hum experience that makes
me feel like I'm a part of something working optimally great.
Good luck!

 

[CharlieB]

Re: 90HP merc problems

Couple of questions,

When you cleaned the carbs what did you find?

When you used the test tank did you have someone pump the bulb?
Or was did they pump the bbulb on the main tank?

You either have a fuel delivery problem , weak fuel pump, it takes off fine then the carbs run low on fuel

or yoou may have a small quantity of water in the tank, alls well til the boat tilts up getting on a plane then the fuel pick-up gets into the pool of water that shifts to the reaar of the tank.

Check the carbs again, look for beads of water in the bottom of the bowls, if none then rebuild the fuel pump.