Yamaha stalls

[steplift20]

I think it's a 03 it's my sons motor

[spareparts]

all the 115 4 strokes were EFI, carb version of that motor was 90/100 hp

[SkunkBoat]

dunno Yamaha but...my zuki 4 stroke had similar problem when you back off.
It was the IAC (Idle Air Control valve). Problem was random for a while but eventually I got an error code on the Tachometer.
There was an adjustment which I did and it helped for a while but then I ended up replacing the IAC valve.

[steplift20]

One thing we noticed is that when we removed the spark plugs the secound one was not in tight it just unscrewed do you think that would cause a compression loss causing it to stall at idle ?

[THEFERMANATOR]

Wasn't sure what HP where they all went fuel injected. I know in 03 there smaller 4 strokes were still carbed engines. Since it's injected, have you checked the throttle body to see how carboned up it is? I believe yamaha uses a pwm style iac, and I'm not sure if they have adaptive iac or not. I know I've had a couple come to me stalling, iac was working fine, but the throttle bodies were so gunked up the iac simply couldn't let enough air by to keep the idle up. Cleaned the throttle bodies, and no more stalling.

It doesn't hurt to put a fuel pressure gauge on it either. I had one years back(think it was a 115) where the boat had sat for a long time, and the vst was full of just nasty crusted up crap from sitting with fuel in it. It would run great for 5-10 minutes, then itwould start stalling. Put a fuel pressure gauge on it and seen the pressure would drop. Ended up having to pull the vst apart, soak and clean everything inside of it, put it back together, and then flush the injectors out to get it back to stay runni,g.

[steplift20]

Spare parts, what's a shift switch and where would it be what foes it look like ?

[spareparts]

Ive been working on too many different engines lately, I think the 115 only has a shift position switch, where as the F 150 has a shift position ans shift assist switch. They are both located at the same place. look where the shift cable ends on the engine, follow the wires to the connection, the shift assist activates when shifting out of gear, stumbling the engine, allowing the clutch in the lower to release. It may be sticking. Spray some lube on the shift slide and work it back and forth. Check the switch for continuity in neutral and in gear