Stalling out of Yamaha 225 4 stroke engine at low idle

[Peterrogers]

I have been battling a stalling out problem on my Yamaha 4 stroke 225 HP engine for years now. I'm at the end of my rope. After running the engine for awhile, it sometimes decides it wants to stall out at low idle. If I squeeze the primer bulb, it will usually restart right way and will run until it decides it wants to stall again. There is no pattern whatsoever to what is going on. Also lately when I squeeze the primer bulb, it stays depressed for an inordinate amount of time. I have replaced both pumps in the engine, all fuel senders, and a host of other parts. I even went as far to install a separate pump to the fuel line just before the primer bulb so there would always be fuel at the ready.

I have put thousands of dollars in to rectify this problem on an otherwise perfectly running engine.

Can Anyone Help Me? Again I'm at the end of my rope and quite discouraged.

[99yam40]

Most good shops should have a fuel system tester that will pump a measured through the system to make sure it is capable of letting proper flow.
Without even running the motor.

If primer bulb does not come back then there is a restriction somewhere.
check valves can cause problems as well as screens in pick up lines if they have them.
Adding an electric pump can be dangerous if not designed for the system

[Nautical]

Fuel line restriction , stuck check valve or the line itself is deteriorating inside with debris.Possible pick up in tank. check suction side all the way back to the tank and may have to clean tank too.

[rodbolt17]

most likely?????
a leaking fuel return check valve.
its located beside the low pressure pump between the VST inlet and the low pressure pump intake.
as the low pressure cycles 10 sec on and 20 sec off below 1200 RPM if that valve leaks the VST runs out of fuel in about 6-10 min below 1200.
all else fails simply watch the fuel in the engine fuel cup.
you will see it go u[p and down about every 20 seconds.
BTW that valve is pricy.

[Solarman]

225-4, idling issues

If the bulb is remaining collapsed, then you have a restriction before the bulb. You should check the hoses - collapsing, water separator/ fuel filter - blockage, vent line blockage - creating a vacuum? But most probably...

Some manufacturers installed a check-valve barbed fitting where the fuel line connects to the tank. This fitting isn't needed, and has caused many problems for boaters. Check to see if you have it, and either punch out the ball inside, or replace with an open fitting. You should also remove the pump you added in front of the bulb, this is not safe.

Good luck, let us know what you find.

[rodbolt17]

that "check valve" installed at the tank is SOMETIMES required by LAW.
read the USCG rules about anti siphon valves.
the life you save may be mine.

your describing the typical lift pump check valve failure that most techs have NO clue why its there or how to test it.

[boscoe99]

that "check valve" installed at the tank is SOMETIMES required by LAW.
read the USCG rules about anti siphon valves.
the life you save may be mine.

your describing the typical lift pump check valve failure that most techs have NO clue why its there or how to test it.

In an inboard or inboard/outboard powered boat, absolutely.

In an outboard powered boat, never.

Very commonly misunderstood. Folks don't read the whole of the regulations.

[Solarman]

Thnx bosco99, you're both right. It is ”sometimes required by law” and the reason for it, when the motor installed is equal to, or below the level of the fuel tank, the valve must be installed. Outboards are not included in that classification. But they do restrict the fuel flow on many outboards.

Just trying to help rodbolt. This owners problem is probably that check valve, and if removed it would not create a hazardous condition, or break any laws.

Good luck.

[boscoe99]

Sounds like we might be confusing an anti-siphon valve (located at the outlet of the fuel tank) with what I am going to call a pressure relief valve that is plumbed between the outlet of the lift pump and the inlet of the lift pump.

I won't have an anti-siphon valve in my outboard powered boats but that is just me. But, my motors have all be mounted higher than the outlet of the fuel tank, such that the fuel hose runs uphill from the tank to the motor, so that if God forbid a fuel hose were to break there is no way for fuel to siphon from the fuel tank.

The pressure relief valve is to unload the electric lift pump if and when the VST if full of fuel. Rather than the pump trying to push fuel and not be able to, the pressure relief valve will open and allow fuel to circulate around and around. It gets hot in so doing but until Yamaha and the other engine makers get on board with having just one electric fuel pump (located at or in the fuel tank by the way) that is a price that has to be paid for deficient design.

If the pressure relief valve is stuck open or opening too soon then fuel will loop around the electric fuel pump rather than flowing into the VST as it is supposed to. The relief valve can be taken out of the equation by clamping off the fuel hose from the valve to the fuel pump inlet. If the motor now runs normally that would lead me to believe that the relief valve is defective.

[rodbolt17]

the old crimp off with pliers trick works well for testing that relief valve.

whatever the gasoline power the USCG REQUIRES by LAW an anti siphon protection if ANY portion of the fuel SYSTEM drop below the top of the tank.

that's the sometimes.

now the spring loaded valves do come in various head pressures to aid in reducing total fuel system vacuum.

the USCG hand book has the head pressure specs and math computations.

the other system is a rollover/electrical unit that I am not fond of because it only shuts off the fuel if the key is off or the boat is rolled upside down.

[tonyveloso]

Check Valve

I had the exact same problem. I replaced the $125 valve that is zip tied to the fuel pump. Fuel starvation problem went away and motor ran great. 6 months later same problem. Come on.

[boscoe99]

Start you own new thread please.