Thanks for the post!

A few things first:

1. How much pressure do you get in the tank before this starts to happen?

2. Is the Oil Fill Cap clogged? Make sure air can vent through the holes at the top.

3. Does the crankcase have too much oil in it? Make sure you have the proper oil amount in the crankcase.

If two and three above check out, then you may have defective Reed Valves in the pump head. This is a cheap repair if so, as they sell for about $4.89/pair. The Valves may not be seating like they should, or they may be sticking, so as to build up too much pressure in the crankcase.

The caps usually have a series of baffles or some medium like steel wool or a piece of foam to trap oil but allow pressure to vent. If it is over-pressurizing in the crankcase it can also certainly be because of blow-by caused by worn or damaged Piston Rings.

BTW, you can find a full breakdown of this unit by clicking on the below link:

www.mastertoolrepair.com/portable-oil-ba...166360-p-746888.html

I hope this helps, and feel free to reply with more info and I'll be glad to assist further if I can.

- MTR

I'm glad to help, happy compressing!

- MTR