Small Engines (Lawn Mowers, etc.): B & S troubleshoot, blown head gasket, blown head gaskets

Question
Good Morning

I have a John Deere Z-225 Zero Turn Mower with a B &S engine.
Engine specs are as follows:

18.5 HP OHV
Model 31P707
Type 0123E1

Machine has 135 hrs on it. Air filter changed at the start of the season and oil changed every 25-30 hrs with the recommended 10w/30.

Last week I went to use the mower and it would not start.  Turned over but wouldn't fire up.  Pull the spark plug and noticed it was dirty(black and wet).  Cleaned the plug and was able to get it to start after several minutes.  Mower seemed to run ok but not great and would occassionally blow some white smoke.  When I got done and went to clean the mower I noticed oil around the fuel pump(vaccuum) and the hole on the front screen of the pump. Oil was also down along the bottom of the engine.  Checked the oil on the dipstick it was a little lower than usual and was blacker than normal.  Couldn't smell anything due to a head cold.  I did some research on the internet and some people have said to check the fuel/carburetor others are saything because of the smoke and condition of the oil and oil coming out of the fuel pump that they suspect a blown head gasket.  They claim that B & S are known for blown head gaskets.  I have a friend who is handy and said he would look at for me.  Probably ask him to do a compression check.  Any thoughts or suggestions of what it might be or things that I should due to troubleshoot?  Sorry for the length of the response/questions. Thank you in advance for your assistance.

Answer
A compression test is a good place to start.  If your friend has a leakdown tester that would be better to tell if a head gasket is blown, even is just a little.

You can clean the valve breather to make sure it is working.  We just remove the valve breather, spray it down with carb cleaner and blow dry it with compressed air from an air compressor.

Another odd problem Briggs engines have had are leaky dipstick o-rings.  If the o-rings don't seal the engine does not hold vaccum causing oil to escape the engine crankcase. This is pretty rare these days.  It is more common not to get the dip stick on correctly which can cause the problem.

Let me know what the compression is.

Eric