Bob,

I would recommend checking your valve adjustment, if the intake valves are to tight the valves will stay open to long and you get backflow into the intake on the compression stroke. A burn't or warped intake valve will also cause this. Try leaving the fuel shut off by keeping the engine stop cable pulled, take the air cleaner off and have someone crank the engine, if you hear a loud hiss or feel air coming out the intake, you may have a intake vavle issue. CAUTION do not put your hand over the intake when cranking it will try and suck your hand in and leave a hicky on the palm of your hand bigger than your fourteen year old girlfreind ever put on your neck. If your engine ever runs away plugging the intake will shut it down but NEVER use a body part that is yours.

Worn valve guides can also increase the amount of oil in the intake and cylinder blowby caused by worn rings and low compression but, both of these would typically increase crankcase pressure and cause you to get a lot of oil in your breather line that goes into your collector. You mentioned your collector has no back pressure, I trust you mean that it is vented and just acts as a collector for the oil mist. If it were not vented it could cause your problem as the engine needs to breath and vent the case pressure. If it does not breath it will force the pressure up and out the intake.

Does anyone have the Universal part number for the airfilter ???

or for that matter hoe about the Kobota part number for the air filter.

Thanks in Advance