1986 Mercury 4hp 2 stroke running rough after half throttle {link for video}

[merc4hp1986]

So to start off here, I picked up this little engine a couple weeks ago knowing that it bogged under load. Seller said that all he did was an impeller change so I was hoping it was a carb issue.

When I took it out on the water the first time I noticed the amount of smoke coming from the engine and the smell of a rich fuel mix and that at WOT it would take a bit to get up to the rpm's, bogging a bit, then would sporadically sound like it was misfiring.

First thing I did was check spark. I noticed that it indeed was getting a consistent spark but the plug was a bit fouled. I changed the plug took it out again for a little ride and checked plug again, again it looked a little oily. I should mention I'm running 50:1

I should say that it's only a single cylinder engine. I decided before I did anything else I'd check compression and was getting 100psi

So then I decided I'd disassemble the carb and give it a good clean. I soaked it pretty good, making sure to clean out all the Jets and passageways. All of the gaskets seemed in good shape and the fuel pump also seemed like it was in good shape aswell.

I tried to find a fuel mix screw but it doesn't seem to have one, only a idle mixture screw.

Fuel lines in the engine look new and also the one coming from the tank, and all of the wires are in good shape. I'll also add on here that I do have some seafoam in the tank, so that might be why it's smoking so much.

My guess now is that it may have something to do with timing or that maybe the spark isn't getting enough voltage under load. But to be honest I have no idea how to fix that, but would learn if I knew that was the problem.. I don't wanna tinker with it if I dont have too. All in all the engines running too rich in my opinion and misfiring.

If someone with a little experience can watch the video I'll upload and give me their opinion it would be much appreciated!
If it's not a good enough video just let me know and I re-upload one thats better.

Thanks in advance!

 

[MDCrappie]

Do you have a test prop on that motor? If not then you should not attempt to run it at that high RPM without a load. Also running in that tank is contributing to the over rich mixture.

 

[airshot]

Use a spark tester to see if the gap is at least 3/16" they are cheap. And yes, the Sea foam will create smoke !! Go ahead and flood the carb by spraying sea foam in the carb while running then shut it down. Let it sit for 30 minutes then fire it back up. After a short run, switch to your regular 50-1 mix with fresh fuel and see if it still smokes a lot. At idle, you will get smoke, but not like it is on fire ! Compression seems good, check spark, it could be weak. Get a factory rebuild kit for the carb, it will give you the proper settings for the carb to get it running plus the fresh gaskets will seal everything up. How good is the fuel line from the tank ? Any cracks or bad connectors will suck air and create fuel mix issues and look inside the tank for crud. Good luck.....

 

[Pappy]

No attempt should be made to troubleshoot this engine at all until a propeller is installed and the proper load placed on the engine, In the water and on the back of a boat. "Troubleshooting 101"