Problem with 70 HP Evinrude Outboard

Yesterday morning the outboard ran great, however, after running for a half hour at 3500 RPMs, the engine started sputtering and coughing. It sounded like there was water in the gasoline. The engine RPMs would drop from 3500 to around 1000, sputter/cough, then jump to 2500. Sometimes the engine would just shut off. I was able to get back to my dock by pressing the choke button when the RPMs would drop to around 1000. The RPMs would pick back up to around 2500, and it would run for a second or two, then sputter/cough and the RPMs would again drop to around 1000. Pressing the choke button would usually work, but several times the engine just stopped. It would always restart right away, but as soon as you gave it gas, it would start sputtering/coughing again.

Thinking the engine may have overheated, I checked to ensure there was water coming out of the engine. The water stream was warm, but not really hot, so I'm thinking it is not overheating. The horn in the console that is supposed to sound when the engine overheats never sounded.

Each time the engine quit, it restarted easily.

Once I got back to the dock, the engine started and idled great.

Figuring this was water or trash in the fuel, I bought a new 6 gallon gas tank and hose. Filled the tank with fresh gas, and tried again today.

Same thing happened again - the first half hour the engine ran very well, then the sputtering/coughing started again. Once again we limped back to the dock by occasionally pressing the choke button.

I have had the carbs rebuilt; had the timing set; new plugs installed.

Anyone have any idea what the problem may be?

Thanks, Bob

Bob,
It seems to me that it could be a fuel supply problem if you use the choke and it improves the RPM's. By choking it, you're cutting down the air flow.

Just a thought

OhioTC18 said:

Bob,
It seems to me that it could be a fuel supply problem if you use the choke and it improves the RPM's. By choking it, you're cutting down the air flow.

Just a thought

Click to expand...

I agree, but can't figure out why it runs fine for a half hour then starts acting up.

Any ideas on what else to check?

Thanks, Bob

Bump.

My 50 hp Mercury did that exact same thing, I took it to a shop and they rebuilt the carbs. Mine is a little 4 cylinder and one of the carbs had the float stuck. The guy that rebuilt the carbs (cost $300) told me that I needed to start unhooking the fuel line when I got off of the water. My boats are always kept inside the shed, he said that the heat would expand the fuel and the one-way check valve in the fuel line would force the needle into the seat (on the float). I told him of all the boats that I have owned, that I had never unhooked the fuel line and he said "I'm only trying to save you $300 in the future" I've unhooked the fuel line ever since.