Blackened spark plugs, and rough running motor

[beer batter]

Johnson 140hp, 2 stroke, 4 cylinder has a hard time starting, will spit and sputter, sometimes even stall out. Pulled all 4 spark plugs and 3 of them were black, while 1 was wet with gas. Installed new plugs, boat ran great for about 20 minutes while I took it for a test run. Went fishing for a couple hours running the trolling motor, went to start the main motor again and same problem - hard getting it started with engine spitting and sputtering. Pulled plugs again, and same 3 were black while the other was again wet with gas.

What do you think the problem is here?

[Wally fisher]

You might want to check you gas oil mix. Im guessing you have a blender that automatically does it for you. But It sounds like you might be running rich causing the build up on the plugs and the crappy performance. The easiest fix would be to trade in that johnson for a yamaha. j/k. I had a similar problem with my old merc that had the autoblender one day it started feeding more oil than needed. I would check into that. Hopefully its something simple for ya.

[beer batter]

The unit used to have oil injection, but I pulled it out and premix the oil and gas for a few years now. I had also thought about the mixture being too rich, but I'm pretty sure the mixture is OK.

[Eric Wettschreck]

Have you checked spark on the cylinder that is wet with gas?

[Chode2235]

You might also want to think about decarbing the engine. Either run the Seafoam or Ringfree shock treatment through it, or get the carbs cleaned rebuilt this winter. My guess is that you just have a bunch of carbon build up in the motor and especially in the carbs.

What kind of oil are you running/mixing?

[beer batter]

Thanks for the suggestions guys. I believe the oil is run-of-the-mill 2 stroke oil sold at Fleet Farm. Don't recall the brand, but I've been using it for years. I'm sure there's more expensive oil, but it has worked for me in the past.

I did not check spark as I was by myself. Couldn't figure out how to turn over the motor and see the spark plug at same time. Someone else will be there this weekend to help debug the issues, so that will be one of the things we check.

Another thought is air intake on the carbs. Perhaps there's not enough air, causing the cylinders to burn too rich. How does one tell if that's the issue?

Thanks again!

[marine_man]

I would definitely check spark, and would probably do a compression test as well.. just to rule the "big" stuff out.

marine_man

[beer batter]

Compression checked out good on all 4 cylinders, Timing light showed spark in all 4, and was pretty much in time. Checked gas and did not see any signs of water in the fuel. Carbs looked real clean but we sprayed some gumout in there anyway as the motor was running and let her sit overnight. Pulled plugs, cleaned them, and reinstalled them. Motor started great. Ran for 10 minutes, pulled plugs again and found 2 blackened plugs and 3 wet plugs. Checked the needle adjustment on the cylinder that was good, and adjusted the other cylinders to that same needle adjustment (they were all within 1/2 turn). Ran again, and checked plugs - 2 plugs looked good, 2 plugs were still wet, but no more blackened plugs.

Tried fine tuning the needle adjustment on the other cylinders, but couldn't get the plugs to run dry. Any thoughts on that?

[boatfixer]

Which cylinders are giving you problems? top 2? bottom 2? Port, starboard?. You may have a diaphram issue in the fuel pump or you may have an inlet needle issue.

Spraying carb cleaner into the throat of the carburator will not clean the carburator.

[beer batter]

The bottom 2 cylinders seem to be running wet.

[boatfixer]

Then we need to look at whats common with those 2 cylinders

Fuel pump--

You could remove the fuel pump and look for gas in the passage through the block.

Carburator--.

When you pump the primer bulb, do you have gas running out of the front of the carb, an indication that the needle is not sealing off the fuel flow when the float chamber is full. You may also need to disassemble the carb and inspect the needle and check float height.

You can also have plugged recirculation hoses. The hoses are needed to recirculate puddled fuel in the bottom of the crankcase.---This would be the less likely of the other possible causes.