1997 mariner 4cy 40hp motor...need mechanical advise please

[bodimizer]

i just purchased this boat ,its a 40hp mariner 97 model with 2 carbs on it,,,cant find out what is going on with it,,carried it to a certified boat mechanic and he told me he coundnt find out whats wrong with it,,,now!!!!....let me explain,,the boat will only turn up to about 4500rpm but rated for 5500rpm,..will not plain off with two ppl in the boat,,heres what i know has been check,,,,,,the motor has 120 compression on all cyclinders ,..timing is perfect,,,carbs have been gone thru 3 times,reeds are good and did verify the correct carbs were on the motor and of course clean glass,,,no leaks or vacuum issues with fuel lines or tanks,,and tired three different props for it with no luck,,,if anyone may know whats causing this or know how to fix it please reach out to me...and i dont need anyne telling me that the to fix it is buy another motor,,,please keep the jokes to yourself..looking for help/advise...thank you

 

[Railroader]

What sort of boat?

If it's a fiberglass skiff type, it may well be waterlogged in the floor, and a 200 wouldn't get it on plane... ?

That little motor is a screamer, and worth keeping!

 

[bilgerat]

what boat is it on?

 

[Whitefeather]

What pitch props did you try on it?
What does the exhaust manifold look like? Is it clear? Sounds like it may be either exhaust gasket or too high a pitch on the prop

 

[bodimizer]

if im not mistaken it was a 13 pitch on it,,stainless ,but a 12 alum.. was tried also ,,the boat is a alweld...and not sure about the manifold,,,

 

[little rascal]

check the spark plugs for moisture. A blown head gasket will cause those symptoms.

 

[Whitefeather]

Sounds like the props aren’t the issue then.

By cleaning the carbs, do you mean taking completely down soaking them in cleaning solution for a day or more blowing out every single jet with compressed air and replacing all rubber o rings and hoses. If it’s had ethanol gas in it that stuff will drive you nuts.

 

[Railroader]

And being aluminum, it ain't waterlogged either...Hope you get it figgered out, running right that's an awesome motor!!

 

[bodimizer]

yes sir ..no moisture on plugs and plugs and an carbs wasnt soaked over night bur took a part ,bown and cleaned 3 times....thx

 

[The Original Rooster]

Dirty fuel filter or faulty fuel pump maybe?

 

[NE GA Pappy]

is the timing advancing like it is suppose to?

 

[beretta]

Maybe fuel volume? Have you tried to add more fuel to it while under load?

 

[Whitefeather]

If changing props wasn’t an issue then it’s either gas or spark. Sounds like a carb issue to me. Ethanol is the Devil on outboard motors

 

[notnksnemor]

At 4500 rpm is the throttle lever bottomed out?
Throttle cable been replaced?
Is it WOT at the carbs?

 

[bodimizer]

may try the fuel pump next

 

[tucker80]

Sounds like a carb issue to me too. It's easy to miss something when cleaning them, or have more trash churn up and clog them back up.
Start at the tank and work your way through. Don't skip or assume anything.

 

[Nimrod71]

I would say the problem may be in the fuel system. If the fuel tank hasn't been cleaned, I would clean it. If the fuel line and bubble haven't been changed I would get new line and bubble. Check fuel line connections. Check motor fuel line connections from connector to fuel filter and replace and clean filter. Check fuel lines from filer to carbs. If this doesn't work I would carry the motor to Dublin Marine for service.

I have owned and operated outboard motors since 1973 and I have had everything from a 7.5 Sears to a 250 Yamaha and I can tell you if the motor cranks without trouble, your problem is something simple, we are just missing it.

 

[bodimizer]

update...replaced the tank ,fuel lines and bubble ,,,,went thru the fuel pump and could tell it already has a new kit in it ...sooooo heres what im seeing on the motor,,,doesnt seem like the filter is holding the fuel it needs too,,,,and its suckin gas twice as it should but no leaks i could find,,played with it on the water today and it ran good tat full throttle till i started trolling,it started shutting off and didnt want to crank back till i startd pumping bubble back up.....

 

[notnksnemor]

A far theory from others, but similar to what I experienced on an '04 Merc 150.

Stator.
Under the flywheel.
Have the voltages checked while running.

 

[Lukikus2]

Just sounds like a bad fuel bulb. But as stated above. The motor can be governed at the carburetor also.