Hello all! Just a quick question: what do i do with the carb spacer rear vacuum port? I have a 312 Mercury and the carb (autolite) sits on top of a pacer with a rear vacuum port. I'm reading that this port is for the brake booster but I'm still with manual brakes. When I plug it the engine dies. Same if I connect it to the pcv valve (nothing normally hooked to the pcv...it just sits there). If I leave it unplugged the engine runs great but it hisses something fierce!

 

A previous owner probably didn't notice that it wasn't plugged and set the idle speed like that. You will need to plug it and adjust the idle speed on the carburetor.

I don't know if the spacer could be stock, but it is either for the pcv valve or brakes.

The engine does need to be able to breathe , so you do need to evaluate it and get the pcv valve functioning properly or install breathers.

 

Ok, that sounds pretty straight forward. I will have to go see if I have something set up wrong because I know the idle and mixture screws are right around 2 revolutions from flush. Maybe I just need to open it up more...what about hooking it to the bottom of the air breather instead of plugging it? I noticed on the aftermarket air breather I bought there is a connection underneath it.

 

The idle mixture screws are not what I'm talking about, but the two turns of the idle screws is usually a ball park initial setting. All engines are different and may require a different position for a proper tune.

What I'm talking about is the screw that opens and closes the throttle shaft for the idle speed setting.

If you connect that vacuum port to the air cleaner housing, you're in practically the same situation, except that the air is now filtered. That's not what you want to do. Either plug it or get the pcv functioning properly.

 

Okay that sounds good... I'll look at it when I get home today and see if I can adjust that. If I get the PVC functioning right what vacuum do I use?? Do I use the one that were talking about?

 

I don't really know. If the carburetor has a port for it, use that.
The spacer is an unknown. If you do use it, make sure it distributes evenly to both sides of the intake.

 

Power brakes were not an option on a 64 F100.