Fuel Milage/bad compression?

[yz125yamaha10]

I had posted a thread a week ago about poor fuel mileage and what i had done.No results from anything.So today i checked my compression (5sfe) cylinders 1,3,4 all had 190psi even. Cylinder number 2 reads 150psi steady.The factory rated compression for my 5sfe is 178psi. I must have carbon build up to make it read 190psi with 99,xxx showing on the clock.But what really worries me is why cylinder 2 reads 150psi.Head gasket?valve?.This surely is the reason why my car averages 10mpg worse than it ever did? if anybody has some help i would appreciate it.

*O and the coolant runs brown now and then*

so far:
new timing set
new fuel/air filters
fuel system cleaning
new tires
new brakes
new plugs wires
tranny flush refill synthetic atf used since new
mobil1 since new
pcv
New o2 sensors front and aft
coolant flush

[Digger1]

YZ,

You may want to squirt a little oil into cylinder #2 and see if the compression comes up. If it does not, then you have ruled out any problems with the piston rings and/or piston/cylinder clearance.

Good luck!