2017 Y15 SMHA Stalls At Idle For First 15 Minutes

[EngineerJohn]

Hi, I've got a 2017 Y15 SMHA outboard that has trouble starting.

The problem(s):

Stage 1: give it 4 to 10 pulls before it starts.

Stage 2: Once it does start, it immediately stalls, no matter how much throttle I give it (0 to full). It repeats this start-die cycle 3 times, reliably, till it actually gets started.

Stage 3: On the 4^th start-up, I goose the throttle to full open to keep it alive. During this stage if I bring the throttle down to idle it will die. Every time. I have to fully open the throttle for 15-20 minutes before it will be stable at low idle.

Stage 4: After 15-20 mins it has no trouble, high throttle, low idle, start, stop, whatever, but if I shut down the engine and it sits for 3 hours then the issue returns and we go back to Stage 1.

Weather here has been ranging from 50* to a warm 70* weather.

This is only really a problem because the outboard only goes into gear when it's in low idle, so I can’t even drive the darn thing while it’s warming.

I’ve tried a lot of different diagnostics and fixes (see list below).


The big question: What should I try next?

Diagnostic and testing recommendations are preferred to suggestions to outright replace parts.

----------------------------------------------------------------

Specs:
Yamaha Y15 SMHA
Year: 2017
4 Stroke
Transom height: S
Serial Number: 1050949
Model: 6AGK

History:
I got this outboard in March of this year. The PO warned me the motor took some time to warm up, but this seems kinda silly. Said he’d been running it all winter.

Things I've tried:
* Replaced all fuel lines & fuel bulb
* Carburetor rebuild * clean, complete with meticulous scrubbing & air hose blowout, jets were not blocked when I took the carb apart
* Pulled and tested the Primestart valve on 12 volts. It works as expected. Yes, the rumors are true; this outboard doesn't have a manual choke.
*Tired adjusting idle screw but if I set the idle high enough to where the engine doesn’t stall, then it’s too high to shift
* I'm starting the outboard in the throttle starting position, and I've tried every other throttle position during startup Stages 1-4 just for fun.
* No error codes
* Running 100% ethanol free gas
* Used seafoam fuel system cleaner
* Pumped fuel bulb while rev’ing down to low idle - no effect
* Checked for fuel leaks - none
* Replaced inboard fuel filter and axillary racore water-fuel filter
* Visually checked all relevant gaskets – they look good
* Checked for Vacuum leaks - nothing
* Pulled and cleaned spark plugs, checked for gap and spark – all good
* Visual inspection of air filter – clean as a whistle
* Read every darn forum post I could find, called three mechanics, and spent days working on the darn thing
* When I store the outboard at the end of the day, I always shut off fuel and let the carb run dry

Things I Have _Not_ Tried But Am Considering:
*Taking it to a Yamaha Service Tech
*Replacing the fuel pump (I feel I ruled that out by testing with the fuel bulb)
*Replacing the carb (that’s expensive!)
* Leakdown test (why would it have to do with the cylinders?)
* Connecting to a laptop and reading data while motor is running, hunting for clues

[TownsendsFJR1300]

Certainly sounds like the Primestart isn't working properly, no extra fuel on start up (COLD).

Is there a "choke bypass lever" you can try?

I believe reading somewhere that a similar issue with a member engine, the Prime start worked but didn't open enough.


Someone else will chime in with better info..

.

[EngineerJohn]

Certainly sounds like the Primestart isn't working properly, no extra fuel on start up (COLD).

Is there a "choke bypass lever" you can try?

I believe reading somewhere that a similar issue with a member engine, the Prime start worked but didn't open enough.

.

Unfortunately there isn't a choke bypass, I called up Yamaha and they confirmed Primestart was the only choke system on the 2017 F15.

If it is the Primestart, how else can I tell it isn't working?

I already pulled the Primestart valve and put it on 12 volts, it moved out a 1/4 inch over 5 mins. My understanding was that was plenty enough. and why would warming up the engine for 15 mins ameliorate the problem?

Thanks for chiming in and let me know if you think there's anyone else I should consult!

[99yam40]

Have you looked in your owners manual to see what it says about prime start?
all of the ones I have seen have a red lever you can switch from normal/auto position to the open position and the off position when needed.

If the needle moves , maybe the passages are plugged up not letting fuel flow

[TownsendsFJR1300]

I already pulled the Primestart valve and put it on 12 volts, it moved out a 1/4 inch over 5 mins. My understanding was that was plenty enough. and why would warming up the engine for 15 mins ameliorate the problem?

Did it take 5 minutes to go that 1/4"?? Please clarify...

If so, I would think that's taking WAY TO LONG to simply open...It should open when cranking COLD, that's when it's needed..


.

[EngineerJohn]

Have you looked in your owners manual to see what it says about prime start?
all of the ones I have seen have a red lever you can switch from normal/auto position to the open position and the off position when needed.

If the needle moves , maybe the passages are plugged up not letting fuel flow

I did look through the owners manual thoroughly, the Primestart system on the 2017 Y15 does *not* have any sort of control system. Yamaha service rep over the phone confirmed this. Which is totally a bummer! I can attached pictures of the 2017 Y15 if you want to see for yourself.

[EngineerJohn]

Did it take 5 minutes to go that 1/4"?? Please clarify...

Under test conditions, the Primestart needle took about 90 seconds to move the 1/4 inch. I let it sit on the 12 volt source for 5 mins total just to make sure it wasn't leaking any wax. It was not. Everything I've read so far indicated 1/4 of an inch is about the travel for these Primestarts. Let me know if I'm off on that.

Regardless, why would the idle issue reliably resolve itself after 15-20 mins of operation? If it was a clogged fuel passageway, you'd think the clog would persist...

[TownsendsFJR1300]

The engine heeds extra fuel when cold(thus the Prime start, or choke butterfly's closed).

Once it's warmed up some, it doesn't need that extra fuel and runs fine (as it should).

In say 30 seconds of initial power up to the Prime start, how much is it opening? A bunch/ little?


I do not know how long it should take to open. Just logic would dictate it should be open (depending on the weather, engine temp, etc) immediately and close once the engine starts/warms.

.
.Here's an old thread, 99 Yam and Rodbolt involved. May help, may not:

https://forums.iboats.com/forum/engi...e-start-system

[panasonic]

The F15 have not changed much in many years. The prime start can be a pain and cause your exact problem. It has no emergency bypass as your dealer told you.

When the engine is cold the needle is retracted allowing extra fuel through a very small passage for starting. As soon as the engine starts, power is supplied to the prime start and it begins to warm up and the needle extends slowly shutting off the extra fuel...this should take a few minutes to occur, giving the engine time to warm up and run at idle.

As you have bench tested the prime start and it appears to work. I would check, installed on the engine, that the prime start vavle it is getting powered after the engine has started. There should be power there at all times when the engine is running.

[panasonic]

Also the enrichment passage that the prime start needle opens and closes is very small and easily clogged. If it is, that engine will be very hard to get going and stay going until the engine is warmed and dosnt require the extra fuel.