i would spend the time to do a cylinder leakage test,but i suspect it is hurt.

A compression test will tell you if the rings are bad, then get some good valve covers w/ vents made for a marine engine, and make sure the oil level is Not way over full,
did you try running one quart low on oil to see if it does the same thing.
Was this your original engine that you changed over, or did you buy it after someone did the work.

I have tried with less oil 1Q less then full on dipstick same thing happends. Will do a leakdown test this week.

Motor is bought as this and not my orginial.

Did 2 houers more yesterday around and under 4000 rpm and works just fine in that range..

I still your breather system not doing the job...

Problem solved , I changed to a high quility oil oilfilter and fuelfilter , got better ventilation in the valvecovers and no more oil is showing.

Realy strange no one here can anser why but it runns fine in 70 mph like 4700 rpm and more to go..

I was so happy that i had to buy a another boat =)

- from your first post

Did I understand you correctly? You are saying that you gained 10+ MPH by simply switching oil and oil / fuel filters and changing your valve cover venting? Sounds like there has to be more to it than just this. Were you running it way lean due to fuel restriction? Did you ever check fuel pressure?

[QUOTE=rsmagnum32;4363253]Problem solved , I changed to a high quility oil oilfilter and fuelfilter , got better ventilation in the valvecovers and no more oil is showing.

Realy strange no one here can anser why but it runns fine in 70 mph like 4700 rpm and more to go..

QUOTE]

Really, this is what I said in post #3

Sounds like to much crank case pressure, are there breathers in the valve covers ? have you checked the pcv valve in the lower half of the intake

Yes i have gaind a lot of speed now my guess is that most of it is from right trim. Engine sems to run better and better the more i run it.

Yes Thanks for the tips but i have not checked the pcv sems to med that there are just hoses to the air filter ?

Had a carb engine before thisone so havent got the right fuelpressergage..

without proper crank pressure venting you have a real good chance of blowing seals in the engine.

Also your reply that no one knew what the problem is kind of funny

The day anyone can fix a boat 100% completely over the net totally blind with a bunch of lacking information is the day you need to go to work for Merc, I am sure they will hire you -

how was the engine built, what maintenance is lacking along with proper parts and the big one what in the hell set up is the engine - is it stock parts built or some aftermarket app parts , Is everything correctly installed , what oil pan and windage set up do you have along with what valve covers are installed ? Do have a PCV valve set up ?

for your fuel pressure what fuel pump ? what fuel set up ? have you tested fuel pressures at rpm levels ?

BUP, to be fair, the OP is living in Sweden, so English is not likely to be his first language. I doubt if knowledge about high performance boats is exactly falling off of trees. In any case, you are correct - without additional data, we are all grasping at straws. It sounds like he found a solution to his problem, and that is great. Still, it would be good to know a little more about the problem and solution - might benefit someone else down the road.