2003 F115 4 stroke stalls at low RPM's

[SaltyKayak]

A couple weeks ago, I was running in from some deep blue fishing. I was running at around 4500 RPM's and doing about 28 MPH. About 1/4 mile from the inlet.. bam.. the motor chugs and stops. Glad I have SeaTow. For the 2 miles back to the ramp, I tried to start the engine several times. No go until we got back to the ramp and voila.. she started. Got home and did an engine anode change, fuel injector change, lower unit change, new spark plugs and fresh Yamaha oil change. I also did a chemical engine flush with Rydlyme and was stunned at all the scale that came out of the engine. Thought all was well.. ran great on my driveway. Launched the boat and ran out to my fav offshore spot about 15 miles out and when I slowed down to idle speed.. the motor dies. Turn the key.. starts right back up and I can idle to my spot. Changes spots several times and when I slowed to idle speed.. motor dies. Turn the key.. back up and idle to spot. Came home at about 4200 RPM's and near the ramp, ease off down to idle.. motor dies but starts right back up. Oh. forgot to mention, I have changed the water/fuel filter and the small internal engine filter. I have NOT tackled the VST yet as both the internal filter and water/fuel filter appeared clean with no debris.
Suggestions as to my next step would be appreciated...

[TownsendsFJR1300]

Might try squeezing the primer bulb when it acts up to see if the VST is staying full..

Checking fuel rail pressure may be helpful as well, especially when it's acting up...

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[99yam40]

VST screen can plug without the other filters showing problems

need to monitor rail pressure to see if it stays in spec, if you do not want to open VST up to inspect

hooking up to laptop might help eliminate some things

[Surfjones3]

Drain some of the gas from the VST to see if there is junk in it, as others stated check the pressure at the fuel rail, if you key on the pressure should spike to apx 37-40psi for about 4sec, if you have pressure then your high pressure pump is working and it’s likely a VST issue. How old is the engine in terms of years and hours? Are you running blended gas ?

[SaltyKayak]

Drain some of the gas from the VST to see if there is junk in it, as others stated check the pressure at the fuel rail, if you key on the pressure should spike to apx 37-40psi for about 4sec, if you have pressure then your high pressure pump is working and it’s likely a VST issue. How old is the engine in terms of years and hours? Are you running blended gas ?

There is about 600 total hrs on the motor with 3 hrs since I last changed p[lugs/filters/and fluids and it has never had E10 gas.. Is there a simple process to simply drain the VST without having to take the port side of the motor apart? Getting to the VST looks daunting for an old soldier to tackle who has never done it before.

[TownsendsFJR1300]

There is about 600 total hrs on the motor with 3 hrs since I last changed p[lugs/filters/and fluids and it has never had E10 gas.. Is there a simple process to simply drain the VST without having to take the port side of the motor apart? Getting to the VST looks daunting for an old soldier to tackle who has never done it before.

Part #14 is the drain plug: https://www.boats.net/catalog/yamaha...injection-pump

Should be able to loosen (NOT fully remove) and drain. My 150 has a drain hose attached, I don't see one on your parts diagram.


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[SaltyKayak]

Part #14 is the drain plug: https://www.boats.net/catalog/yamaha...injection-pump

Should be able to loosen (NOT fully remove) and drain. My 150 has a drain hose attached, I don't see one on your parts diagram.


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Thanks for the diagram and pointing out the drain plug. I will see what I need to do to get to it....