vaccum leak?

[Anonymous]

I have a 1970-ish Ford 250 CI straight six and replaced the stock breather with one of those chrome 3 or 4 inch diameter breathers. The engine runs really good with it on there, but when I remove it, the idle drops a couple hundred RPMs and it starts running a little rough. I never noticed this in any other engine I've had. Could this be a vaccum leak somewhere? I have replaced both vaccum lines and checked the ones that are plugged and none seem to be leaking. Also, I have an exhaust leak at the donut gasket and another before the muffler, could this affect performance?

 

[CobraSix]

Sounds like you are running lean which means either your idle mix is off or you have a vacuum leak.

Slade

 

[MustangSix]

Some engines respond that way because the PCV is now sucking near atmospheric air directly thru the valve cover. The engine is probably developing very little blowby and the crankcase pressure is fairly low with the breather in place. You'd get the same response if you pulled the PCV out of the cover, I'm sure.

I think it's nothing really to worry about.

 

[Anonymous]

I noticed the engine ran a little smoother when I plugged the line running to the PVC valve, but then it starts spewing stuff out the oil filler cap at higher RPMs. Guess I'll just not worry about it then, thanks.

 

[BIGREDRASA]

Make sure the PCV valve works. It'll help your engine live longer by purging crankcase fumes.