Mariner 90hp 3 cylinder 2004 - Bogging Driving Me Crazy

[MaltaBoating]

Hi everyone. I have a 90hp Mariner 3 cylinder, 2 stroke, 2004. It was garaged for several years and after I acquired it and its boat, I was delighted by its condition. After months detailing and repairing the boat and running over the basics on the engine I put the boat in the water.

The engine bogs but it’s erratic. Sometimes it runs like a dream, gets beyond 30 knots and all seems perfect, it can even pull a water skier or a tube. At other times the power goes up and down like a yo-yo with a mind of its own. Often it won’t even get up on plane, or just cuts out. It is very erratic.

Out of the water, without any load, everything works, performance is faultless. I have eliminated fuel, fuel lines, tank, fuel filters (by using an external, brand new tank with new lines and filters), compression is 125 psi per cylinder, every fluid in the engine has been changed so it is fresh, and I have had an engineer check it over. Still no joy and it is driving me to the point of insanity. Having scoured the internet, I believe I have narrowed down the possible issues to:

Ignition stator failure on high side.
Idle mixture/low speed mixture badly adjusted.
Dirty jets or carburetors.
Fuel pump or gaskets in fuel pump not working.
Coils/CDM have issues.
Reed valves are problematic.
Electrical temp sensor failure.

Can anyone help me? Did I get the list of potential issues right?

 

[wn6ngp]

The thing that makes this difficult is that it is intermittent. Otherwise I have had similar issues that were fixed by
1 cleaning carb and jets
2. small adjustments of the carb needles bog on launch, 1/4 turn of screw fixed it.
3. rebuilding the fuel pump( careful with this one to note exact sequence of gaskets, it will run mostly even if you get some of those gaskets out of sequence I have had similar problems to yours after goofing up the rebuild sequence.
4. I had trouble with sticking thermostat, motor would not warm up properly, then hard to start eventually causing plugs to foul. A motor that age should have thermostat at least checked.

My experience with running engines outside of water is meaningless. Without the water back pressure on the exhausts they seem to run fine no matter the problem.

My 1999 merc model elpto 90 hp the electrical temp sensor just activates an alarm no impact on performance, ie no limp mode etc so I don't think that's it.

You didn't list checking out the fuel and or vacum hoses which could be sucking in some air.if they have come slightly loose somewhere.

best of luck with your debug. Let us know how it goes.

 

[SteveVT]

Not eliminating anything on your list, but as a specific additional suggestion, especially due to intermittent nature: if a piece of crud (like a bit of rubber fuel line is floating around in your carb fuel bowl, it can intermittently clog the float valve, or HS jet, then get free again.

And just because tanks and lines were replaced and new filters added, it doesn't mean that an older bit of junk from before the replacement effort is still in the carb. And no solvent (like SeaFoam, etc.) can remove it, if rubber or plastic. It has to be physically removed.

Not saying that's absolutely it, but that particular bug can do the intermittent thing. There may be others, but I'd crack open the carb, if it was me, and have a look-see.

 

[skey]

i have seen the trigger cause problems similar to what you describe. I would not rule out fuel delivery

 

[Texasmark]

I too have had fuel issues caused by deteriorating fuel lines on that engine at 10 years of age....2002 in 2012. Found little black specks of fuel line in the high speed jet (bottom of carb bowl on one cylinder) and in the in the low speed area...top of carb under the plate on another cylinder. Took a swab to the fuel lines at the carb and came out with little pieces of line. Other thing is that if you see fuel around any line/connection be suspect. Good time to see specs is with the primer bulb squeezed up hard...should stay hard with engine off....if not, cracks in fuel lines or needle valve in a carb not seating properly...could cause flooding when running.

Loss of power in the water vs on muffs is the engine asking for a richer mixture to handle the higher load imposed on it for a given RPM.

 

[MotorboatinKJ]

Hi everyone. I have a 90hp Mariner 3 cylinder, 2 stroke, 2004. It was garaged for several years and after I acquired it and its boat, I was delighted by its condition. After months detailing and repairing the boat and running over the basics on the engine I put the boat in the water.

The engine bogs but it’s erratic. Sometimes it runs like a dream, gets beyond 30 knots and all seems perfect, it can even pull a water skier or a tube. At other times the power goes up and down like a yo-yo with a mind of its own. Often it won’t even get up on plane, or just cuts out. It is very erratic.

Out of the water, without any load, everything works, performance is faultless. I have eliminated fuel, fuel lines, tank, fuel filters (by using an external, brand new tank with new lines and filters), compression is 125 psi per cylinder, every fluid in the engine has been changed so it is fresh, and I have had an engineer check it over. Still no joy and it is driving me to the point of insanity. Having scoured the internet, I believe I have narrowed down the possible issues to:

Ignition stator failure on high side.
Idle mixture/low speed mixture badly adjusted.
Dirty jets or carburetors.
Fuel pump or gaskets in fuel pump not working.
Coils/CDM have issues.
Reed valves are problematic.
Electrical temp sensor failure.

Can anyone help me? Did I get the list of potential issues right?

Ever figure this out? I’m in the same boat and it’s very frustrating. Replaced stator, trigger, switch box... ugh! Any help is appreciated.

 

[Texasmark]

I usually try to isolate it to fuel or fire when it acts up. Fuel is a squirt of Sea Foam into the venturis of the carbs checking for a response or not. Fire is checking to see that the plugs are firing, like running with the cowl off and a timing light attached to each (in series) spark plug lead to see if fire is present and constant.....but this doesn't answer the "is it in proper timing" question unless you put the light on the timing mark, triggered off #1 and check against the spec. Once you have that answer it's much easier to move forward.