250 Mariner offshore efi Oil Problem (long)

[Jomomma76]

Hi fellas, new to the forum! My Marine buddy told me to post my problem here, that you guys know whats up!
Motor is a 1998 Mariner offshore efi 2 stroker. I bought it on a 1973 Starcraft Chieftain converted to center console. Bought the boat for what I thought was a good deal. Previous owner fired it up on muffs, ran great, idled great, pissed a strong stream of water out the telltale. Shifted great, ran it for a good 10 minutes with no issues. Could not run it on the water because the old quicksilver accu-plate I think, had a broken electric pump motor that would need to be replaced, no problem.
Brought it home, found it had a rotten transom underneath several coats of rhino liner. Decided to ditch the jack plate and mount it directly to a raised transom. The guys that redid the boat in 07 added steel tubing to the floor and a big L channel across the stern for extra support. So by the time I got the transom done it had been a good three months before I got to take it out. Noticed the motor smoked more than what I saw in the yard when I bought it. Pulled it out of the water and noticed it had leaked black sutty mixed oil out of the exhaust bypass tubes above the cavitation plate down on it and down the lower unit. Thinking it was probably coming down the driveshaft and out the bottom I pulled the lower unit to check. Everything was dry as a bone inside the driveshaft tunnel and the exhaust coming down. Inspected the powerhead and found the top starboard cylinder’s coil pack was unplugged on the harness side tucked in very hard to see(nothing I did). Plugged it back up took it out this past weekend and it ran better but still leaked oilout the bypass tubes and down.
Checked the compression, I have a little over a hundred in all but one cylinder and it is around eighty. Strange but all the plugs looked the same, no difference on the low compression cylinder. The top starboard plug was fuel washed so I changed it, but none of the other plugs look like I would expect for how much oil is coming out of it. Figured I would try to block off the oil pump and try to premix to see if maybe the oil pump is throwing too much fuel. Noticed when I pulled off the oilpressurereliefvalve for the external oil tank that fresh unmixed two stroke oil still green leaked a good half cup or so out of the valve onto the floor of the cowl then down the foot the ground. It did this with the oil reservoir removed and the oil pump removed and blocked off overnight. Motor runs very strong, idles around perfect and I have seen 50mph on it by my Lowrance letting off with plenty left. No other leaks under the cowl. Just trying to get the oil leak under control, I can live with it down on power for a year or so to get the wife off my butt if I have to rebuild it now. 90% of the time I’m cruising 10 mph and under looking for fish. Any help would be greatly appreciated! Thanks for reading my book!

[Capt.Insane-o]

You have to put a pipe plug in place of that check valve before you catch yourself on fire. Thats raw fuel from the crankcase running out of the cowl.

[Jomomma76]

It is already plugged now, just was wondering if it was normal for oil to run out of the check valve. Plugged it off that next morning. I’ll make sure to clean it all real good before I fire it up again.

[Jomomma76]

Thank you Sir!

[Jomomma76]

[billybob]

Thank god. You plugged off the oil tank pulse fitting. These motors always run rich at low speed even when warm. The excess fuel runs down exhaust tract. Breaking the carbon loose. And create a black puddle of gunk, under motor. It is normal.

[Jomomma76]

So it is normal for that much oil to run out? The picture I attached over the oil coming out of exhaust bypass was before I pulled the oil injection. Thanks for the help Sir!

[Capt.Insane-o]

Its coming up to operating temp on both banks?

[Jomomma76]

Comes up to around 140 or so. Checked all the cylinders with a temp gun, they all about the same.