Very high idle when breathers hooked up

I'm having multiple issues with my motor currently that I believe one of the possibilities that are causing them are a crankcase pressure issue. My engine has the moroso
billet positive locking breathers ( part number 68788) on each valve cover. Originally I had both breathers just left open venting to the air. Now I am almost convinced that I have too much crankcase pressure building up causing my rear main seal leak. So I left the one breather open as an inlet for air into the engine and I hooked the other breather to the pcv port on the front carburetor. The engine seems to start a little easier and not run as rich as before, however I cannot get the idle speed lower than roughly 1800 to 2000 rpm. I have the idle speed screws backed all of the way out on both carburetors but it still idles very high. Am I missing something with how these breathers are supposed to be hooked up?

Dumb question but does the throttle linkage have a little slack?

I don't believe so, but I will double check. Are you referring to the slack between the linkage from the front to rear carburetor, or in the throttle cable to carburetor?

intake gaskets

I tried checking for vacuum leaks around the intake and I couldn't find any. The idle is around 900-1000 without the breathers hooked up. Wouldn't this rule out the intake gaskets? Engine vacuum is low, but I'm not sure if that's just because of the camshaft though. The motor has less than 200 miles on it and I've had nothing but issues since the day I ordered it.

Talking about any of the linkage that my be holding the throttle open a little.

what engine is it ? intake could be leaking on the underside in the valley,

528 hemi. Stock 2x4 intake

Start it and get a can of brake clean and spray the heck out of it around the intake and carb base's. Do one area at at time and listen. It won't hurt anything and doesn't leave a residue like carb cleaner. Check the throttle cable and make sure it has some slack in it. If that checks out than on the carbs it could be the the idle screw on the slave carb keeping it idling too high if your running progressive. If it's 1 to 1 it still could be that when you lower the idle screw out all the way on the one carb the other carb idle screw is stopping the linkage from idling down.

I run this breather on one side and a pvc on the other.



Found this on my hemi using the brake clean method. It had us stumped because it didn't sound like anything we ever heard maybe because it was leaking at the top and front at the same time???

Perhaps a silly question, but you do have a pcv-valve installed somewhere right?

Another check, as already referred to:

Disconnect the throttle cable from its stud on the carb.
See if the carb's linkage closes, then see if the cable end goes on smoothly or you need to crack the carb open a bit.
Might have to lengthen the cable a little.
I've had that happen even by just pulling a carb & reinstalling.
Also, if the carbs have been off, see if the butterflies are all closing with no interference from the intake.

As for running a PCV valve & breather, that's good.
There are adjustable PCV valves on the market if you want to fuss with that, some guys really like them.

I will double check the linkage tomorrow. There isn't a pcv valve at all. Just one of the breathers that I have listed on each valve cover. I found that strange, but that is how I received the engine right from the engine builder. I called moroso earlier and the guy told me that these breathers are meant to be used with an evacuation system tied in with the headers, and by having one of the breathers hooked up to the carburetor it may be pulling too much air into the motor leaning it out and causing the high idle. I just find it strange that it is making that big of a difference just by hooking a breather up.

I will check for a vacuum leak at the intake as well when I refill all the oil in the motor and I'm able to run it again.

By hooking the breather up to the carb with out a PCV valve you created a big vacuum leak.

I checked the linkage. There is slack in it and nothing seems to be binding.

Is the engine running too rich?

When you say hooking the breather up to PVC port on carb , most breathers are hooked to the air cleaner housing.unless the breather has a proper working PCV valve in it . If not don't you have a open port..Maybe try putting a PCV valve with rubber grommet in one valve cover and the other side breather to air cleaner housing and see if it does better. This is a waste of time if the engine will not idle wright with no breathers and all PCV ports plugged. Just thinking out loud

I agree with Stumpy after rereading your post you added a huge vacuum leak. That breather is not meant to have vacuum on it. The result you're having is the same as if you just pulled the plug off the pvc port on the carb and left it open. You need to take that off and if needed add a pvc valve.

I see it know as well how it created a vacuum leak. I'm not too sure how I didn't realize it at the time. The engine is running very rich, so by having the carburetor draw all of that extra air in, it leaned out the mixture causing the idle to jump up that high. I was originally only running the hose from the breather to try and help eliminate any pressure that may have been building up inside of it.

you sir should try one of these. I have one, I'm a believer.

http://mewagner.com/?p=444