40 HP Mercury 402 smoking and dying

[bunk02]

Fired up my 79 Merc 402 for first time in 2 months (yes that's a crime) and she was really hard to start. Once she did she smoked a lot more than usual. After about 30 minutes I realized that there was a bigger issue; she was still smoking a lot and started to run erratic. Eventually she lost all power and stalled while full throttle. Fired it up again and it ran for 30 seconds and died. Tried adjusting throttle to every position but couldn't keep it running. Luckily I brought my backup tank and switched on a whim. She smoked a little more then evened out and ran better. Of course at that point I was freaked at the thought of being stranded on the lake so I headed back to dock. I know this probably sounds obvious to some of you, but does this sound like a bad gas/oil mixture in my first tank...or even cheap BP gas??!! Gonna be 90 degrees and sunny this weeks so I wanna boat.

 

[Traceyh]

Re: 40 HP Mercury 402 smoking and dying

Heres my guess based on what you have told us.
You left the old gas in the tank for 2 months, vent open, hot weather.
You were using premix, gas evaporated off leaving and overly rich mixture of oil to gas in the old tank. oil=smoke, plain and simple, and the only place for the engine to get oil is from the premix.
You switched to backup tank which was either fresh fuel, or had the vent closed preventing gas evaporation, and the engine ran better.
New spark plugs are in order, as well as new gas in the main tank.

Now it is possible that I am way off base here, but based on the info you gave, that is my educated guess.

Hope this helps.

 

[bunk02]

Re: 40 HP Mercury 402 smoking and dying

Went ahead and drained all old gas out and remixed a small 3 1/2 gallon mix of 50:1. Also added a can of Seafoam to the new tank. She fired right up and after a minute or two the smoke pretty much ceased (back to usual at least). I ran her around for about 40 minutes at a reasonable cruising speed, then when I was coming back in and close enough to solid ground that I felt safe doing so I put the throttle down. She hesitated just a tad but then took right off at full speed. I'm still a little paranoid about the situation so I may try and replace the plugs anyways. Of course the biggest problem with that is the fact that she is docked and I don't have a trailer so it'll be a matter of hanging over the back of the boat or wading chest deep in nasty canal water!!!!

 

[bunk02]

Re: 40 HP Mercury 402 smoking and dying

Alas, I post to soon. So with fresh gas again, mixed with seafoam I fired her up a week after the initial problem. Just like the first time she smoked excessively....I took her out of the canal and instantly felt uneasy. It sputtered and stuttered but didn't quit. Before she had a chance to konk out on me I took it back in, a whole 2 minute trip!! So I stopped at the parts store and got two new plugs, gonna try putting them in on Sunday.