Home Forums Hunting & Shooting Hunter's Campfire Outboard Motor Problem

Hi, I have an older-!980?- Evenrude 40hp outboard motor. It wasn't started for 5-7 years, has been stored in a heated garage. It started right up, but it has a miss every 5 seconds or so whether on idle or half throttle- I'm running it off the garden hose with earmuff type hose connections. I had it tuned up and only put maybe 25 hours on it before I stored it. When I take the sparkplugs out after running it they are wet and black. I used new 93 octane gas, new hose and connections. My other motor runs great with this setup. Any ideas?
Thanks, Mike

93 Octane...I have a 96 Mercury 150 efi a mechanic told me years ago to use 85 or 87 octane I use 87.Don't think a old motor needs premium octane I could be wrong.

Use real gas, not the crap mixed with alcohol. Check your mixture on the carb.

Sounds to me like it's running waaaaay rich. The only outboard I am intimately familiar with is a 1991 135-hp Mercury, and it does not have a choke like an automotive carb does but rather a solenoid that dumps extra fuel into the airflow. You may have a sticky mechanism or something else causing the excessively rich mixture.

Did ya hit it with a fogging oil before putting it to bed or just put it away expecting the carb not to be gunked up the day you decided to fire it up?

Have you replaced all the fuel lines under the cowling? None of them are ethanol approved. If you haven't done it yet, you need to replace all these lines, including those super small ones running to the carb. They rot from the inside out. When you take one of the old lines off, let some of the gas drip on a white towel. If there is black residue in it, you've found your problem. You'll also need to rebuild the carb to clean out that residue.

Fogging oil does not prevent gum and varnish build-up. That's what Stabil and SeaFoam are for . . .

@ Dan and Walt - Where did the OP state he was using ethanol blended fuel?

If I recall 1990ish mercury 40-70ho engines had a separate oil tank so you didn't need to run pre-mix...
What I don't recall is if they are OMC and when it started....

Is your fuel well mixed?
Is your air filter clean?
Are your floats stuck open?

It's a 41 year old outboard. Unless he is the original owner and is certain he's used ethanol free gas for the past 41 years, the problem is as I've outlined above.

Maybe check and replace the points, plugs, and condenser (assuming it isn’t electronic ignition). Check the spark plug wires. I got a 1960’s Johnson kicker to work after sitting inside a barn wrapped in a plastic bag for over 20 years by filing the points, spraying the carb with gumout, and replacing the fuel lines from the tank to the carb. Don’t forget it will need a new water pump impeller.

Where did he say otherwise?

Curious - I've never seen that stuff before.

So, if you spray that into the cylinders, how does that prevent gum and varnish buildup in the carb?

Fogging oil is mostly to prevent internal cylinder corrosion. Right?

Sounds like bad float needle seats. Pretty common problem since ethanol came on the scene. It allows too much unregulated fuel into the cylinder, causing fowling and missing. I have 2 snowmobiles sitting out back right now that need new float needles and seats before winter.

Yes.

Here is the structions off the SeaFoam Fogging Solution can.
With the older OB's it's in through the carb as I run the last gas out for the season, then I pop the plugs out and add another squirt for good measure.

Absolutely critical with four-strokes unless your into replacing injectors.

And why wouldn't adding Stabil and/or SeaFoam into the fuel tank and running the motor at season's end achieve the same thing?

If it's been stored for that long, you can just about guarantee the carb is gummed up and the gaskets are probably leaking from drying up in storage. A carb rebuild will probably take care of your problem pretty quickly if you can find the parts. I just did this on a 35 hp Merc about the same age and it wasn't too difficult at all. Check the online marine supply stores and eventually you will find the parts you need.. There are youtube videos on it if you've never done one before...

If it has been stored that long, best to check your lower unit seals also. A very good chance they are dried up and starting to leak also and need replacement. Check your lower unit oil for discoloration caused by water migration and you'll know right away if there has been a leaky seal...

Bob