Merc 115 stalls at 3/4 throttle ?

[Radradney]

So very new to boats the boat we got 1978 glastron with the old 115 tower of power for 8 years got it in the water and it ran great once it got good fuel running through it and half of the second day Then it started to stall out at 3/4 throttle so around 25-30 and 4k rpm I'd guess. motor has not had a tune up or any thing yet since we got it. Have noticed a stutter now and then. Would I be right at thinking it's a carb issue bad air fuel mix? The feeling I get from the sound and how it's acting but I only know carb truck motors

 

[Chris1956]

It would be unusual for carbs to suddenly stop working while you are on plane. More likely you have a fuel restriction. Check the antisiphon valve and fuel tank vent.

Make sure the fuel filters are clear. Make sure the fuel lines are at least 5/16" ID. Rebuild the fuel pump, and inspect the pulse lines that power it.

Another possibility is that the wiring on the engine is bad, allowing the spark to short out. Check for missing insulation. Also check to make sure the switchbox is getting good solid battery power on the red and adjacent white wires.