Removed Oil Cap - Different Results

[brianhiggi]

I'm trying to identify an air/vacuum leak on my '78 SC. I took off the oil filler cap when the engine isn't at full running temp and the rpms drop a lot. When I take off the oil cap when the engine is hot the rpms don't noticeably drop at all. What does this mean?

[JJ 911SC]

Check the WUR plumbing

[aerodyn930]

In line with your suspicion of a vaccum leak, What you are describing points out to your mixture being a little lean, A lean mixture will affect the engine operation more when your engine is cold, As such be cautious of a backfire (airbox explosion) until you get it sorted out,

Let us know what you find , Good luck, Lou

[brianhiggi]

JJ 911SC, I am not an ace mechanic so what do you mean by WUR plumbing?
Lou, could the lean condition be the cause of my car being hard to start? My WUR was tested on another SC and it worked fine.

[JJ 911SC]

Check the Vacuum line that control your WUR if it was tested in another car.

Also if you are suspecting an air leak, spray some Quick Start aroud the Vacuum lines and connections of the items in the diagram below. If the RPM goes up, you got a leak.

#5 is you WUR

Vacuum System Layout




WUR