Outboard 115 yamaha misfiring at low revs

If your 115 Yamaha SHO VMAX outboard engine is experiencing RPM fluctuations at speeds over 3500 RPM, it may be due to a few different factors. Here are some things to check:

1. Fuel supply: Make sure that the fuel supply to the engine is consistent and free from any debris or obstructions. Check the fuel filters, fuel lines, and fuel pump for any signs of damage or clogging.
2. Spark plugs: Check the spark plugs to make sure they are clean and functioning properly. If the spark plugs are worn or dirty, they may cause the engine to misfire at higher RPMs.
3. Throttle position sensor: The throttle position sensor (TPS) sends a signal to the engine control module (ECM) to adjust the fuel and air mixture. If the TPS is not functioning correctly, it may cause the engine to fluctuate at higher RPMs.
4. Air intake system: Make sure that the air intake system is clean and free from any debris or obstructions. Check the air filter and air intake hoses for any signs of damage or clogging.
5. ECM software updates: Check with your Yamaha dealer to see if there are any available software updates for the ECM that may improve the engine's performance.

If you are unable to diagnose and fix the issue on your own, it may be necessary to take the engine to a professional technician for further diagnosis and repair.

Hey Pete.. this sounds serious.... will it rev up while in neutral? If it revs freely and high.. the power head should be ok.. if it will NOT rev up freely and high.. STOP - you are causing more damage..
Check the compression with a good gauge..it should be 125psi minimum.. with no more than 10 psi difference between any two cylinders.. DO this WITH the THROTTLE WIDE OPEN...
Can you turn the propeller by hand while it is in neutral?..Of not.. this is the problem.
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You can buy the repair manual here:
http://www.fish307.com/clymer-115-250-hp-two-stroke-outboard-jet-drives-1999-2002-b789/

We do not have the info you are asking for. Sorry.

2003 Yamaha 115 4 Strokes Operation and Idle Demo ...

? 2:29
www.youtube.com/watch?v=sMmionreldM
Dec 29, 2012 - Uploaded by Peter Richards Engines for 1989 Larson boat with dual 115 Yamaha 4 StrokeEngines. ... Outboard Yamaha 150 HP DIRTY idle JETS, Motor will not idle .

more info needed but it sounds like fuel,maybe water like condensation

very basic carbs ! clean all jets and emulsion tube then check the float needle is clean and the tip isnt grooved , blow threw all ports etc and then refit and set the mix screw 1.5 turns out for starters then run up in a tub of water and fine tune till its happy to idle and rev up ! make of engine ??

Engine or gearcase seized...
Remove the recoil starter ( 3 bolts and the startingear link)
If you can turn the flywheel slightly: Gearcase seized
If you can't turn the flywheel at all: Engine seized.
In both cases: If you can't disassemble and have the job done yourself, forget that motor...

sounds like a bad coil or trigger. Find the offending cylinder with a timing light and physically move the coil to a good firing cylinder. If the problem follows the coil, you have it, if not you need a trigger,

clean carbs and check set up !

fuel pump could be the cause but also the float in the carby could be not set at the right level and starve the motor at high revs .