1997 90hp Merc acting strange

[armyH20Dog]

I have a 1997 90hp Merc that i bought new in 97. Every year it gets winterized as well as checked out before i take it out in the spring. I am unsure of the total hours I have on it, but I know its alot.

When I took it out for what I believe was the 4th time this year. It started great and ran perfectly for about 5 minutes on plane, then died. I checked the bulb and it was soft. Thinking I ran what fuel was in the motor, I re-primed the bulb and it started right up. Again I took off and after about 500 yards it died again. When I checked the bulb it was firm and I started it back up. This time, when the motor started, I noticed there seem to be a ticking sound coming from the motor. At this point I headed for the ramp. The motor seem to run fine at lower RPMs (aside from the ticking sound).

When i got it home i changed the plugs (they only had about 4 hours on them and looked good), changed the fuel filter (also new) and added a fuel treatment in case i had water in the fuel due to the heavy rain we received prior to taking the boat out. I stared and ran the motor at the house with the hose hooked up to it. It started fine, but again it died when it got up to about 4000 rpms and the ticking is still there(it sounds like its coming from the power head). In the 12 years i have had the motor, I have never had a mechanical problem.

I am currently not working due to an injury, and can't afford to take the motor in and get it looked at. Is this problem im having a minor problem that i can fix myself, or is my boat sidelined till I can afford to get in the shop. Any ideas that y'all might have would be most helpful.

 

[Joe_the_boatman]

Re: 1997 90hp Merc acting strange

I have no idea what the ticking noise could be. You'll need some tools if you want to start diagnosing and repairing your engine. They're not expensive though. I'd start with a compression tester ($25) and a digital multimeter ($10). You'll also need standard shop tools, and you'll probably want a shop manual ($10 on ebay).

Get a trash can and fill with water so you can run your outboard while testing it. I'd take a compression reading first to make sure your pistons are OK. Start troubleshooting the fuel system next. Do some searching here at the forums to try to find a problem similar to yours. Good luck.

 

[CharlieB]

Re: 1997 90hp Merc acting strange

First thought is that your fuel pump may have weakened and in need of attention, however the 'ticking' noise leads me to think that it may be too late, you may have a damaged top cyl from going lean, overheating that piston long before the cooling system heats enough to alarm.

Pull the lanyard, disconnect the fuel line from between the pump and the carbs, stick it in a suitable container, squeeze the primer and watch the flow, now crank the motor and watch the flow, it should be strong steady spurts, sort of like regular small squeezes of the primer pump. If noticeably less then the fuel pump needs rebuild.

The top cyl may have gone lean as the fuel pump weakens and cannot provide the pressure and flow to the top carb, piston heats and tries to stick in the cyl. It may not be obvious looking thru the spark plug hole, compression may not be noticeably low, but the 'ticking' noise may be that piston skirt melted and smeared on the cyl wall. You will have to remove a side cover or exhaust plates to look inside thru the ports to be sure.

 

[saumon]

Re: 1997 90hp Merc acting strange

First thought is that your fuel pump may have weakened and in need of attention, however the 'ticking' noise leads me to think that it may be too late, you may have a damaged top cyl from going lean, overheating that piston long before the cooling system heats enough to alarm.

Pull the lanyard, disconnect the fuel line from between the pump and the carbs, stick it in a suitable container, squeeze the primer and watch the flow, now crank the motor and watch the flow, it should be strong steady spurts, sort of like regular small squeezes of the primer pump. If noticeably less then the fuel pump needs rebuild.

The top cyl may have gone lean as the fuel pump weakens and cannot provide the pressure and flow to the top carb, piston heats and tries to stick in the cyl. It may not be obvious looking thru the spark plug hole, compression may not be noticeably low, but the 'ticking' noise may be that piston skirt melted and smeared on the cyl wall. You will have to remove a side cover or exhaust plates to look inside thru the ports to be sure.

As he said, except for the last part. There's no cover or exhaust plates on thoses triples to have a look. Crankcase must be splitted and crankshaft pulled to look at the pistons (i know, it's not a good news, sorry...)