Briggs and Stratton 350 series leaking oil out of the exhaust

Hello I have a Briggs and Stratton 350 series Murray mower and I just got it from a friend who does scrap metal and said he found it at the side of the curb
When I first got it it would not start at all it was the valves one of the seats came out so I re seated the valves and it ran for about a minute then stoped and was spitting oil like crazy so I changed it and then tried it again and it was still leaking but not as much I came out this morning to work on one of my other mowers and I had to move this one so I thought why not try and fire it up and sure enough ran for about a minute at the most then dies again still leaking oil so I did another oil change the second one in less then 2 months
I made sure all the oil was out of the engine I even took the muffler and the plug out and cranked it about 10 times
I put the new oil sit and settle in for about 3 hours then I just went out and cranked it and still spitting
I have also drained the gas both times I did oil changes
I have checked the oil fill and it is not over filled it is right under the full mark if not right on
I don’t know what else to do it is becoming kind of a pain washing oil off my driveway
I also have replaced the spark plug and have done a compression test
It will run very quietly not loud and as soon at you move it it will die
It only has 40 psi compression
Any ideas on what I can do to get it running
I just want to sell this thing and get it out of my yard
I have now named it the mower from hell
Please help me get it running again
Thanks

The 40 psi kind of answers the question. I would be looking at valves not seating, bad head gasket, or cylinder/ring issues.

IL Engine I think he has the newer E series that came out about 5 or 6 years ago.....


Riley I think you need a new or good used head on your engine..... 40 PSI is normal for that engine because of the ACR on the cam....

I get 40 or 50 PSI all the time on engines like that.........

Riley when you are pushing the mower is the carb and air filter on the left side ??? Is so you have the engine I spoke of....

Wal Mart handles that line line of mowers and the cheapest one they have is 200.00 dollars with the tax.......... That style engine is coming in my shop more often this year than the past few years......

Let us know Mon Ami ~!~!

Correction 450 series

It is the 450 series the gas tank is on the right side
The engine says dom feb 2011