After a while of looking to why my 78 400(new jasper) was idling rough, I found a small vacuum leak in the pcv system.

When I pull the hose off of the check valve on the oil fill cap and plug it it idles much nicer, but blows smoke out of the breather on the other valve cover. When I put it back on it goes back to idling rough with fluctuations in the vacuum, no steam. The check valve is still loose, and the breather isn't connected to anything since I have an aftermarket air cleaner. Most of the rest of the vacuum is removed and blocked. Any Ideas?

Thanks

 

I'd try a dry compression test followed by a wet compression test. Sounds like worn rings if it won't run well with the PCV system closed. This assumes your breather can actually draw in fresh air (assuming so since it's disconnected).

 

Smog valve fits into rubber grommet that fits into oil filler cap.

 

Its a brand new jasper engine with less than 2 hours on it.

 

I went through 3 ! before I got a good one back about 98 , from Them . I ran a compression test on the first one , ALL Over the place ! 2nd one would happily run , but mixed coolant and oil within 2 min. ! 3rd one was fine . I have not seen issues with their products recently , My shop installs many of their engines and trannys . We use their rear diffs some times also . Any one can make a mistake . Yours is in assuming there can be nothing wrong with a reman .

 

Replace the PCV valve & change oil (brands).

 

That doesn't change the diagnosis. It's doing what it's doing regardless of what it is. I can empathize with your frustration. A round of compression tests will eliminate all doubt. Hopefully I'm wrong.