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Ivan K
09-09-2019, 03:27 PM
Heyya! First time post after long time lurking!

I bought a used boat 2 or so months ago that had been sitting for a year. Its running a 2003 40hp Merc 2 stroke - I immediately had the carbs cleaned out after buying because it wouldnt stay idle without stalling.

I've been out 6-7 times, and have ran about 24 gallons of fuel though it, most of it has been trolling.

Yesterday, at full power, while making the first run of the day, the engine revved down to 4k, and wouldnt go past it - sounded okay, but just wouldnt accelerate. I changed 2 of the 3 spark plugs (the 2 that had the most black on them), and that seemed to fix it issue - engine ran fine after that.

Now today I just realized something - I never added oil to the reservoir since buying the boat. It was full when I got it, and even though I cant say for sure, I dont think the level dropped much.

Bringing me to the first question - Do these oil injected engines barely use any oil at trolling speed? since that's most of what I've been doing?

second question - What would cause the spark plug to turn black and apparently stop working?

I noticed that the motor blows alot of smoke when I first start it, and then after about 2-3 minutes, the smoke pretty much disappears ( but it still smells). Is this normal for an oil injected 2 stroke? I was under the assumption that 2 stroke all smoke.

RickM46
09-10-2019, 03:24 PM
I have a '92 40hp 4cyl 2 stroke that smokes like crazy at start up (due to heavy choking) but after running a bit at 3000rpms, the smoke decreases quite a bit to the point of being barely visible but you can still smell it if the wind blows it at you.

If you are concerned about oil injection, on mine, there is a clear vinyl tube running from the oil tank bottom to the oil pump and then another clear vinyl tube from the oil pump running to the fuel line where the tube dumps oil into the fuel - both tubes should be blue showing flow of oil. After my engine was 23 years old, the vinyl oil lines hardened and fractured and started leaking but I caught that at the beginning of that season and replaced them before damage could be done. Not a bad idea to visually inspect yours.

If you are doing a lot of slow speed running, you may eventually clog the relief exhaust ports (2 small holes just below the power head in the rear) and then your engine will no longer idle - see http://www.marineengine.com/boat-forum/showthread.php?459940-Yesteryear-92-Merc-40-Idle-Problem-Solved-in-1994

Ivan K
09-16-2019, 11:53 AM
UPDATE:
Replaced all 3 spark plugs with brand new ones.

started fine - but wouldnt go past 4k in RPM again.
This time I let it sit for a while, maybe an hour, then started it back up. When I pushed WOT, it bogged down even worse and wouldnt go past 2k RPM. At really low acceleration, it was making a decent vibration and a very rapid rattle. Sounded like a lawn mower on cocaine...

fastjeff
09-17-2019, 06:20 PM
Check plugs and see which cylinders are running.

Jeff

Ivan K
09-17-2019, 07:16 PM
Check plugs and see which cylinders are running.

Jeff

Did a compression test today.
120
125
130
respectively in cylinders 1 2 & 3.

fastjeff
09-18-2019, 07:58 AM
Where any of those plug running wet, dark and ugly?

Jeff

Ivan K
09-18-2019, 08:13 AM
Where any of those plug running wet, dark and ugly?

Jeff

Bottom plug is dark and a bit wet