I'm using Pennzoil air cooled. It will blow a black spot on the grass when running. The instructions say to run about 6gal for full break-in. I soldered a brass tube on the diaphragm hole and ran the tubing thru the firewall hole( it just has about a 2in hole through the firewall) to about the wing tube. I'm going to try to do more adjusting and then pull the engine and remove the carb to check for dirt and inspect the reeds. It is a rear induction engine. BTW I also tried to tape up the top cowl vents to change the airflow to no avail.