Oil cap, crankcase pressure and idle?
 

When checking the oil on a 79 sc today, I noticed the idle noticeably go down when I took the oil cap off. Idle went back up as soon as the cap went back on. I can't tell you how many rpms as the tach is currently not working. Any ideas to the cause?

This is normal.

If it did not do that I would worry. As stated it is perfectly normal and indicative of a healthy system.

Oil cap, crankcase pressure and idle?
 

It didn't do that in my last sc. I guess that is telling since this one runs MUCH better. :) thanx guys.