My 73 F350 doesn't seem to be breathing well, when I pulled off the oil cap there was a lot of Vacuum, (Sucking in air). The PCV is connected to the vacuum port at the back of the carbs base. The edelbrock oil cap has a hose from it to the vacuum port at the front of the 4 bbl carb. I have now installed a breathable oil cap with no hose outlet and plugged the front carb port thinking that the vacuum ports are right across from each other and are perhaps creating a vacuum? I know the hose from the oil cap is supposed to go into the air cleaners base. Also when either one of my gas tanks get low there is a lot of vacuum when removing the caps, are the caps supposed to be the vented type gas cap because mine are non vented. Any help would be appreciated.

 

I'm not sure what your set up is so my response is "generalized"... The hose from your oil cap should be going to the air filter assembly so that the hose from your pcv that is under vacuum is circulating clean air. It sounds like you have vacuum at your oil cap and PCV so there is no circulation. So I don't know why you would have had the oil cap hooked to a vacuum source if you know that its suppose to be hooked to the air cleaner.
There is normally two options for venting the fuel tank. Either you have the evap system which is a line running from the tank up to a cannister near the frame rail in the engine compartment with non-vented fuel caps or you have a non vented tank with vented fuel caps. Verify what you have and then you should be able to get more accurate advice.

 

Agreed.

Motor needs to inhale - through one unobstructed valve cover opening...and exhale - through one PCV connection to manifold vacuum.

 

@miketaheny, The motor is a 390 with edelbrock performer intake manifold and the Carburetor is a edelbrock 2207 650cfm. Is the connection at the air cleaner also not a vacuum source? I checked for vac canister in engine compartment and there is none so truck needs vented caps.

@FilthyBeast. Thanks for the positive feedback. Guess I just had it set up wrong. I am headed on a camping trip this weekend and have to climb two passes pulling a loaded toyhauler so I need the engine to perform at peak efficiency.

 

The air cleaner connection is not a vacuum source - just an (inhale) air source connected to the right valve cover grommet. A plain ol' breather would work as well.

And, you're welcome...Have a nice trip!

 

Just to caveat on what Filthy Beast said and to maybe provide a more detailed explanation: The connection at the air cleaner is not vacuum as stated but is the inlet for clean air into the engine. The PCV valve is connected to a vacuum source and is sucking fumes and what not out of the engine and back into the intake to be burned and exhausted while at the same time pulling clean air into the engine through the air filter and entering the engine through the oil cap...

 

True and true....

Sounds like an easy one to sort out.

Beautiful truck man, have a fun and safe trip.

 

Hey thanks everyone, Next is timing, the truck seems sluggish at 10 degree timing, I have heard people running as much as 16 degrees without issue but that 18 is to much and it will ping, I am going to try 14 degrees and take my timing light and dist wrench along with me. I put in a new distributor already along with a full tune up (cap,rotor,plugs,wires) and a new coil. it just seems I have to push it pretty hard just to make it to 55mph when towing. I think a F350 with 4 bbl 390 with a C6 and 4:10 gears should be able to maintain 55 without to much issue. The trailer loaded though is about 8,300 lbs. The trucks door tag states 10,000 gvwr.