40hp mariner enging stalling under load

[pedroofn19]

hello I have a 1993 40hp mariner that starts well untill the throttle is pushed forward and then it stalls. If i lift the warm up lever a little it will go into gear and run fine, and then i can push the warm up lever back down once the boat is moving. But as soon as the engine has been put into neutral and into gear again it will stall before the boat starts moving unless the warm up lever is raised. The engine has had a full service recently, and runs fine apart from stalling. The engine starts well and goes into gear fine when it is out of the water and has the muffs on. I dont know much about engines so any help would be much appreciated.
Is this just a case of the engine not having enough revs once put in gear?
Please help.

 

[sdverne]

Re: 40hp mariner enging stalling under load

Let me know if you get an answer, I have the same problem with my boat right now. Thanks

 

[MacDaddy21]

Re: 40hp mariner enging stalling under load

Have you tried squeezing the primer bulb as soon as you put the boat in gear? if it picks up the revs and starts running better you will know it is fuel related, and you can go from there. I would also pull the plugs and see if one or multiple plugs are fouling. Personally it sounds like it is fuel related or carb related. You said the if you lift the warm up lever it will go into gear and run fine. If I remember correctly, the warm up lever just opens the carb throttle plate up a little more, allowing more fuel into the motor. so if it runs fine with the warm up lever raised, that tells me it isn't getting enough fuel, so I would look at checking/replacing fuel lines, fuel filters, and maybe pull your carb(s) and go through them.

 

[pedroofn19]

Re: 40hp mariner enging stalling under load

MacDaddy21 thanks for you reply, i agree with you that it is probably fuel related. I have been told that it could be fuel/air mix is not rich enough. I know very little about engines so all the advice is much appreciated. I have been told to turn the screw on the carbs 1/4 of a turn clockwise and see how it goes after that, and I will have to have the boat in the water to test it. So what you have told me seem to be spot on, thanks. I will probably do it tommorow and I will post the results on here after so sdverne can try the same thing. Thank you.

 

[CharlieB]

Re: 40hp mariner enging stalling under load

Turning the idle mixture screws IN will LEAN the mixture, wrong.

Back the idle mixture screws out (CCW). If this makes any improvement it is a sign that the carbs should be taken OFF, disassembled and fully cleaned as mineral/crud deposits have restricted fuel flow enough as to affect performance.

If the idle mixture is restricted, how much is the main mixture reduced? A lean main jet WILL melt a piston.

Order carb kits, clean the carbs, and while you are taking good care of your motor, how long since the fuel pump had a kit as well?

 

[pedroofn19]

Re: 40hp mariner enging stalling under load

CharlieB thanks for the advise, the carbs and fuel pump have had a sonic clean (whatever that means) when it was serviced. The engine has had about 15 hours of running time since the service. It has new fuel filter and diaphagms in the fuel pump. As I said I know very little about engines so I dont want to do anything that will ruin the engine. It was the man who serviced the engine who told me to turn the screw on the carbs. Any other ideas ?

 

[CharlieB]

Re: 40hp mariner enging stalling under load

If the carbs were just cleaned and adjusted WITHOUT being on-the-water, then it is a good possibility that the idle mixtures are set too lean.

Initial setting is 1 & 1/2 turns out from LIGHTLY seated. This should give enough fuel to start. Final adjustment must be done on-the-water and in Forward gear. Adjust each screw to best idle speed, then further open each screw an additional 1/8 turn out to provide the additional fuel necessary for acceleration.

Test acceleration by rapidly opening the throttle WOT, any lean cough, bog, or slights hesitation proves a need for additional idle mixture fuel. Open each scre another screwdriverblade width and repeat acceleration test. Repeat to perfection. Have the boat loaded as you normally run it as a heavier loaded motor requires more fuel than a lightly loaded boat. Adjusting with a low fuel tank then going out full and attempting to pull up a tube or skier will be too lean act hesitate terribly.

 

[pedroofn19]

Re: 40hp mariner enging stalling under load

CharlieB thanks again.

Yes the carbs were cleaned without the boat being on the water, and since the cleaning I have had this problem.
So I will turn the screw anti clockwise a tiny bit at a time, and test it each time I move the screw by rapidly opening the throttle to WOT untill it is doesnt stall, while the boat is in the water. Is that right???
Also at the moment when I do open her up to WOT I can smell the fuel quite strongly, is this because the fuel/air mix is too lean???
Sorry to seem a bit stupid on this matter but I know so little about engines, and I dont want to ruin my pride and joy.
Thank you for you advise, it helps me so much.

 

[sdverne]

Re: 40hp mariner enging stalling under load

So I also found out that if I push in the choke restricting fuel flow ( done by my key in the ignition because I have a Johnson 130) that I can get it into gear. So should I try the same procedure as pedroofn19?

 

[CharlieB]

Re: 40hp mariner enging stalling under load

Test spark on each cyl using an adjustable gap tester set to 7/16 inch, look for a hot blue arc, any less and the cyl may not fire when the throttle as wide open as the additional air once under compression acts as an insulator, radically increasing voltage necessary for the spark to occur. Any weakness in an igniton will cause misfires and fuel odors with throttle opening.

Double check that no flooding from any carb or any other fuel leaks. A fuel pump diaphragm will leak fuel into a cyl, flooding it and spilling into the water, causing odors.

 

[Jeff Lindquist]

Re: 40hp mariner enging stalling under load

Keep me in the loop on this one as well. I am having same problem with an 80 hp mariner with same description, although i am confident that between idle screws and advancing or retarding the spark advance arm on the port side of the motor, it can be adjusted. ran perfect 2 weeks ago, but this weekend past performed as you described under load. I am also gonna grab a timing light as all wiring and coils tested fine, with perfect driveway testing. Thanks

 

[pedroofn19]

Re: 40hp mariner enging stalling under load

Oh dear it is all sounding a bit complicated to me, Im just a novice when it comes to engines. I will give the screws on the carbs a twiddle and hope that cures it, if it doesnt then I will get someone else who knows what they are doing to do what I have been advised here. Thanks for all the advise guys. I will let you know how it goes after Ive had the boat on the water.

 

[pedroofn19]

Re: 40hp mariner enging stalling under load

Well I sold the boat now so my friend can sort the problem. Thanks for all your help guys. Thank you very much.

 

[charliemckee]

Re: 40hp mariner enging stalling under load

Hey I know this is an old thread but this is happening to my 75hp mariner at the moment. There was a bit of fuel in the water after it stalled a few times, is this normal for a flooded engine or is there likely to be a fuel leak? Should I take the same approach as above or does the bit of fuel in the water mean that its a different problem all together?

This is my first boat and I am very new to all of this so any help would be fantastic.