Mariner 40hp 1986 outboard not revving high please help, lots of stuttering

[PatrickMonahan]

Can anyone tell me from this video of my engine revving at full throttle what is wrong please? Thanks


https://youtu.be/HOOETCxBY8I

The 2 carboretors have been cleaned and I don't know why it is sputtering at high revs, I got a new fuel line and bulb so I don't understand what the problem is, I have also have 2 new spark plugs on it

It just keeps stuttering at high revs and i dont have a clue what it is, its definetely not the carborettors, please help and reply thanks!!!

 

[gm280]

:welcome: aboard PatrickMonahan. Nice to have you join us...

Before we can answer that question, remove the cowl and verify there are no mechanical problems stopping the engine from opening the carb up to wide open. Sounds like there could be something holding it from going open. So with the engine not running, throttle up and verify the carb(s) are opening up all the way first. If so then report back. If not then something else is stopping them. JMHO

 

[tommarvin]

If the carbs open fully, it must fuel, but it's getting fuel, ignition seems fine.
Rebuilding carbs is not that easy. Did you get a full rebuild kit, with all new gaskets, jets, o-rings etc?
Could it be an air leak in a carb gasket, or o-ring leak sucking air at high RPM?

 

[GA_Boater]

I sounds fine to me in a 34 second sound bite masked by wind noise..

Do you have a tach in the boat and what is WOT RPM? Have you checked compression with a gauge and spark using a spark gap tester. A strong spark is needed at higher RPMs.

 

[PatrickMonahan]

thank you for all your replier, much appreciated, lovely warm welcome, have tested the compression and it seems to bve aroud 120 psi for each cylinder, I am wondering is there something like the fuel pump stopping it from revving smoothly and highligh, it seems to be quite an intermittent proble, it will rev high and smooth sometimes for 1 to 2 mins and then bog down, the person who i got the boat off never had a fuel filter anywhere on the engine or on the fuel line which is stupid, it seems to be easy to start but i am still puzzled by why it is stuttering at high revs, has anyone else had this problem with a similar engine??? AND IF THEY HAVE CAN THEY PLEASE REPLY PLEASE, i would love to know what is gouing on but i am young and dumb and inexperinced with these things, it revs up very high in neutral when there is no load on it but when there is a load on it it bigs down into stutters and vibrations, new spark plugs are fitted, could it be the fuel pump?? or is that highly unlikely

 

[PatrickMonahan]

i am going to see what the rpm of the boat is under load at wot very soon

 

[PatrickMonahan]

here is another video of it yesterday

 

[Faztbullet]

Is it a dual coil or single coil model???

 

[PatrickMonahan]

Thank you for all your help. I took out the thermostat and found it to be broke in two ways, 1 that it was not closing and 2 the top part/collar on the thermostat was broke off or broke off, i have ordered a new thermostat today, what was happening was that the engine was running cold and there was oil building up on the spark plugs resultig in poor performance due to the spark plugs being covered in dark black oil , the engine was never warming up so hopefully in a week when i get the thermostat it should run properly thanks

 

[PatrickMonahan]

Heres a view of the engine, should the lever shove the magneto more and also there is a loose switch that either maybe needed to be tightened one way or another also in this video