1999 90 hp 3 cylinder 2 stroke mercury no power, sounds fine

[sms986]

Was out tonight and I took the boat down to my usual spot. Ran fine. Fished for a few hours then I went to leave. Boat got up on plane but wasn't going all too fast, maybe 3/4 throttle speed at full throttle. Dropped it down again and putted for a bit. Opened it up and only got about half throttle speed out of full throttle. The motor sounds just as it should at half throttle, but I've got it at full throttle. Checked the linkage briefly at the ramp and the throttle is opening up all the way.

I have no indication to the problem from sounds or feel. No excessive shaking or vibrating, have a good stream of water coming out, and it sounds just fine. No missing or erratic sounds. It's as if I've got it at half throttle and all is well, but I have it all the way up to full throttle.

I've got one of the two leads to the oil reservoir unhooked. The reservoir is a little on the low side, but it's got about 3/4 of a quart left in it. I've been letting it go down to make sure it's working as this is a fairly new boat to me. Initial thought was the guardian system limiting it, but I'm getting no beeps at all.

And ideas? I'm going to tear into it tomorrow.

 

[racerone]

Have you checked oil pump output ?------Check compression , post your numbers.----Test spark.---It must jump a gap of 3/8" on all leads.----Water in the fuel ?-----I can not see or hear your motor so up to you to do some checks.----Why are the 2 leads on the oil tank unhooked ??

 

[sms986]

Unhooked the oil tank because the beeper was always going off, even when I was half full or better.

Compression in all 3 is 120.

 

[dingbat]

Conventional wisdom says to fix the problem......don’t disable alarm

 

[sms986]

@dingbat Got another tank ordered. Float had to have gone bad and I used it all day thursday and friday. Couldn't tolerate the constant beep.

 

[sms986]

I've got spark on all 3 cylinders-checked with a spark jumper. I also put it on muffs and it would run on each cylinder individually (only ran for a second or two before I shut it down). I've put a tank of gas through it over the past few days so I know the gas is fresh, and I wouldn't have any reason to suspect water in the fuel after looking it all over.

 

[racerone]

Check flywheel key.-----Check fuel pump diaphragm.

 

[Texasmark]

Unhooked the oil tank because the beeper was always going off, even when I was half full or better.

Compression in all 3 is 120.

Your magnet that operates the safe switch for oil in the tank came unglued and fell off. You can cut the tank open, reglue it and glue your tank back together (that process was given to me by a person in the repair business so he must know the tricks on what makes it work), or buy a new tank, or pull out one of the 2 blue wires connected to the tank, from the engine to remote control connector pigtail and check your oil level prior to leaving on every outing......I do....for the same reason on a 2002 115.

 

[Dukedog]

when you say "half throttle" do you mean position of throttle? what are tha rpms? do you mean tha throttle is all tha way foward but its only moving at what is normally 1/2 "throttle"?.. need ta know what tha rpms readings are when its maxed out with throttle at wfo?

 

[sms986]

Don't have a tach on the boat.

What I'm saying is that when I've got the throttle all the way forward, the boat rides/sounds like it does when I would normally have the throttle advanced halfway. It's almost like the throttle is only advancing halfway at full throttle, but I checked everything over (linkage and butterfly valves) and I'm definitely opening it up all the way.

 

[sms986]

Flywheel key is ok.

I got carb rebuild kits, new fuel line, diaphragm rebuild kit, water pump, and a bunch of other stuff. Guy I bought the boat from lied to me big time once already, I'm sure he was also lying when he said he was up on maintenance.

 

[Dukedog]

Don't have a tach on the boat.

What I'm saying is that when I've got the throttle all the way forward, the boat rides/sounds like it does when I would normally have the throttle advanced halfway. It's almost like the throttle is only advancing halfway at full throttle, but I checked everything over (linkage and butterfly valves) and I'm definitely opening it up all the way.

no tach?.. think (not positive with tha "little" motors) it should have a stator with a high side and low side.. when high side gives up tha motor will act as normal (starts fine, idles fine, no grunts, groans, funny noises, misses, runs smooth) jus will not turn over 'bout 3 grand no mater how far ya push tha throttle..

 

[Dukedog]

never mind me.. misread tha year.. its a cdm motor... sorry.

 

[racerone]

Report the results after you do the fuel pump and carburetors.----Or maybe there are some seagull feathers stuck in a reed valve.

 

[sms986]

Carbs looked pristine, but rebult anyway. Same with fuel pump.

Got 2 questions

First, there is one adjustable needle on top of the carbs. This was set to 1 1/2 turns out. Sound about right?

Second, beside this needle, there is an open, threaded hole. Is something supposed to go there? looks like it goes straight into the float bowl.

 

[Texasmark]

On checking the fuel pump and was ok, you may have missed THE smoking gun....diaphragms loose their plasticizers over the years and get stiff. A stiff diaphragm doesn't pump much fuel.

The hole is probably a vent or a manufacturing necessity, like "freeze plugs" in an engine block...have nothing to do with temperature and everything to do with getting the casting material to flow as designed.

 

[Faztbullet]

That is the fuel bowl vent.....some models have a metering jet installed..yours dont.

 

[sms986]

I figured it was a vent, but didn't know if anything should go there. Looked like a big hole and a place for dirt to get in.

I did change the diaphragms on rebuild. They were stretched and a bit worn.

 

[sms986]

So I took it out today. Seemed to do just fine. Idle was pretty high though. Not ridiculous, but not "normal." It would surge, then sneeze, then drop down, repeat. Only thing I can think of is the small felt gasket on the underside of the cover that I left off because it was all mangled up and I couldn't get it to stay in place, but that doesn't make much sense either. Could be an air leak somewhere, but I have no idea where to start on that one and everything is so compact that hitting it with propane anywhere would cause the idle to go up.

 

[Texasmark]

Well an air leak is a great idea.....you can start with your fuel lines. If they are OEM they are way overdue for replacement.