OMC I/O starts but only runs for a min then shuts down

[dave33222]

Ok so my omc I/O 4 cylinder engine starts up but will only run for about a min and then it dies. I warm it up to about 2,000 rpms but it just wont' stay there the rpm needle just slowly drops and it shuts off. I have checked the mechanical fuel pump and it seems to be pumping gas. I have also checked the carb to see if there is water in it. I have changed the fuel filter. The engine is getting spark. I just can't figure this one out. Anyone have any other ideas.

I also just sent my boat in 4 weeks before and i took out and it ran flawlessly.
So it can't be anything to major.

 

[a70eliminator]

Re: OMC I/O starts but only runs for a min then shuts down

Are you running on muffs? Observe the exhaust, flapper's notoriously rot off and block the exhaust exit.

 

[dave33222]

Re: OMC I/O starts but only runs for a min then shuts down

No i flush the engine all the time./

 

[Lodgepole]

Re: OMC I/O starts but only runs for a min then shuts down

You said you checked the fuel filter. There is one where the gas line goes into the carb as well as the filter/water separator canister that looks like an oil filter, in the line from the tank to the fuel pump. Did you check both? Sounds like a fuel delivery problem. If both filters are ok, you may need to test fuel pump pressure. While you are at it, check to be sure fuel tank vent is clear.
I had a flapper fall off on a OMC 3.0 HO and it pluged part of the exhaust in the drive. Made it cough abd backfire at speed but low speed was OK. You will find the flapper just below the bulging rubber boot below the riser elbow connected to the exhaust manifold. Doesn't sound like a flapper to me but should be checked from time to time.

 

[a70eliminator]

Re: OMC I/O starts but only runs for a min then shuts down

Does it start right back up again after it dies? Bad ignition switch would stall right away after letting off the key, it does seem fuel related, give the throttle a pump after it stalls while looking down into the carb, if it doesn't squirt than your running out of fuel. If it blows your head off than my bad.

 

[Don S]

Re: OMC I/O starts but only runs for a min then shuts down

Here in the North West, we suffer from carb icing this time of year. Especially now.
40's temp, lots of moisture.
Try this.
Remove the flame arrestor nut, but leave it on. Then start the engine. When it dies, quickly remove the flame arrestor, open the choke plate and look at the throttle plates. Bet they will be covered with white frost.

 

[Lou C]

Re: OMC I/O starts but only runs for a min then shuts down

Back in the old days...when we had cars with carbs...usually there was some way of heating the intake to reduce the possibility of carb icing (hot air duct from the exh manifold to the air cleaner) but in a boat this would be hard to do because of the water cooled exhaust....doesn't get hot enough...

A couple of other things that can cause fuel delivery problems that are not so obvious...a corroded anti siphon valve (it's a spring loaded valve on the gas tank...that closes under spring pressure...to keep gas from siphoning into the bilge if the fuel line leaks). Normally the fuel pump can overcome the spring pressure and suck gas through but if the ball inside corrodes it may stave for fuel. The other is the tank vent...If you temporarily remove the gas cap and it runs OK that's it....