Yamaha stalls

[steplift20]

115 2003 4 stroke I was out today with my son and his 115 4 stroke yams stalled at idle, when we ran the engine it seems fine when your going but when you idle down it stalls out what can I check with a 4 stroke engine? Thanks for any replys

[spareparts]

first thing do a completer tune up, new plugs, fuel filters, compression test and spark check. If the plugs are dark and fouled, check the engine oil, if its over filled, dark and very thin, you probably have a stuck thermostat. Replace the spark plugs, thermostat and change the oil. If the plugs look fine, check the shift switch to make sure its not sticking, it will shut two cylinders down at low rpm Next, get some one with a scan tool on it and check for codes, and check the Idle Air controller, beyond that, id have the injectors cleaned.

[THEFERMANATOR]

2003 should be a carb engine, shouldn't it?

[steplift20]

Ferm It's a fuel injected

[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 ?