Power loss and speed loss on 4 cylinder 40 merc

[Sporty72655]

My 1990 40 hp mercury lost power and about 10 MPh over the last week, I've been through the carbs. I did check the stator and trigger they did ohm out good. The alternator wires were melted together at the connections. The trigger and stator physically looked good. Could the alternator cause this problem? Is there anything else I can or should check? Thanks

 

[Texasmark]

The alternator and trigger stators are two separate circuits. You don't need the alternator to run the engine. You do need the output of the rectifier/regulator to drive the tach (grey wire) so no alt. no tach. Battery needs to be up to supply adequate power with no recharge capability.

You need to figure out if your rectifier is shorted or you have a power "robber" down the line that is pulling your voltage down where you aren't getting adequate fire to your plugs. That's where I'd start.

 

[Sporty72655]

Thanks, makes sense. The wires weren't touching but they were very close and enough insulation was missing that it could have been arcing between them at higher output. The rectifier only has a few hours on it and ohms out according to the manual. "Which seems somewhat vague btw" I am going to try and get it in the water in the morning to see if repair of the wires fixed the problem

 

[Sporty72655]

Well had it out today. Whatever I did I made it worse. Ides fine but that's it. No power and only 6mph. Originally would do 30mph

 

[racerone]

The trouble shooting on an outboard starts with a compression test.--------Always the first thing to do.---------Then check for spark on each lead.------Spark test is not done with sparkplugs.-------Spark must be able to jump a gap of 3/8" or better.-------A plugged carburetor leaking fuel pump diaphragm can also be an issue.------Waterpump has been checked ?

 

[Sporty72655]

All that has been done. I have a very strong blue spark, good compression, the fuel pump diaphragms were new last fall. I had the carbs stripped down and cleaned them, found nothing in them

 

[Sporty72655]

Water pump is new too

 

[racerone]

More trouble shooting is required on your part I guess.-----Fixed a 4 cylinder Mercury a few years back after dealer threw a bunch of new electronic parts at it.----I did real trouble shooting and owner said ---" thank you very much " for helping me.

 

[Texasmark]

You didn't mention fuel, fuel lines clogged, fuel lines inside and to the engine cracked, fuel filter clogged. If you have fresh fuel when you firewall it and it doesn't respond, squeeze the bulb and see if you get a response. If so you have fuel line problems since you have already redid the fuel pump and it apparently worked for a time after repair.

 

[Sporty72655]

Fuel lines are all new and clear. The lines and bulb from the tank are new. The bulb is pumped up and no difference when pumping it

 

[Texasmark]

OK, get an aerosol can of Sea Foam which contains mineral oil and can be used safely in 2 strokers. Get access to the carbs venturis. Hammer down on the throttle and shoot varying amounts, aka squirts in each venturi. If you got a hit when you did that, you are chasing fuel. If not you are chasing spark.

Have you checked your timing and your throttle-carb butterfly-ignition timing linkage. At WOT obviously the butterflies must be parallel to the venturi. The timing would vary from near zero at idle to as much as 22BTDC at WOT.