I have the return oil line ran from crankcase to front mounted oil cooler ,then into a spin on oil filter &return to the tank. Around town had no problem,but a few miles on the road it wanted to overheat, would almost stop running but limped home.I did a carburator change, thought that was it ,no change.Barely limped home again. Thought I had the oil lines switched,return with vent.So I ran the vent? line to the top of the tank & my other line to the oil cooler & filter.Then after about 3 miles on the highway oil starts pumping out of the cap on my oil tank & just keeps coming, but it ran better. Limped home again mine &the ladies legs covered with oil. I determined the line I now have to the top of my tank is the engine return oil line, but why the problem when i run through the cooler/filter.

 

are you useing a twin cam oil filter?if so,replace it with a regular evo filter(i assume its not a twin cam motor)
kirby
vee twin racing