HELP! Our White 18hp B/S Commercial mower is running but the power is reduced significantly. The air filter was clogged and we found it with oil puddling in the area. Changed the filter, started it up and and it was once again low on power. Opened up the air filter, it was quite dirty again. Removed the filter and power returns. However, a wet mist was spraying up out of the carb. -- seems to be oil and gas. Also, black smoke present until the air filter was opened up. The engine had a short block rebuild less than 100 hours ago. What do we try first?

BREATHER!!! try a new one if oil is coming out of the breather hookup.