I would like to ask someone with a stock 351W (5.8L HO, 4V) engine in their truck to go look under the hood and answer a few questions:
1) The two large tubes coming off of the top ends of the carburetor,what are they for, and if I have removed the emiss. from my truck, should these tubes be left open, plugged off, or connected to vacuum?

2) Does the tube attached to the oil filler cap go to the large port in the air cleaner housing?

3) Where does the PCV valve tube go to, one end goes in the valve cover, where does the other end neeed to go?

4) Does the vacuum line to the distributor vacuum advance go to a primary vacuum port, or to a port on the carb? Which one?

Thanks in advance for your time and trouble. I'm trying to put my motor back to semi-stock configuration, minus smog equipment.

 

First chance I get I'm going to go look up the info you're looking for. I'll get back in a day or two.

 

The answer to #2 is yes. There is a filter that this tube plugs into in the air breather.

 

>1) The two large tubes coming off of the top ends of the
>carburetor,what are they for, and if I have removed the
>emiss. from my truck, should these tubes be left open,
>plugged off, or connected to vacuum?

I don't remember two large tubes, but one of them probably goes to the carbon cannister. I removed mine, plugged the tube and left the gas tank vent to the cannister open.

>2) Does the tube attached to the oil filler cap go to the
>large port in the air cleaner housing?

Yes, this draws the clean air into your crankcase.

>3) Where does the PCV valve tube go to, one end goes in the
>valve cover, where does the other end neeed to go?

This is the return line from your crankcase and should go to a large port at the base of the carb to recirculate crankcase gasses.

>4) Does the vacuum line to the distributor vacuum advance go
>to a primary vacuum port, or to a port on the carb? Which
>one?

You can run it off of either. The primary vacuum port will give it a lot of advance at idle, while if you choose the timed port off the carb (I believe it's the passenger side port) then the vacuum is shut off during idle. The recommended port is the timed port and I found that my truck runs better off the timed port. This port starts to open up and offer vacuum to the distributor at around 900-1000 rpm.

>Thanks in advance for your time and trouble. I'm trying to
>put my motor back to semi-stock configuration, minus smog
>equipment.

I removed all of my smog stuff a while ago and I'm glad I did. I still run cats to pass inspection, but I've removed the carbon can, smog pump and associated air pipes, and EGR. I replaced the restricted air cleaner with a 4" open element along with headers and true duals all the way back, plus a bunch of other mods.

Slik

 

The two large pipes on the carb are probably bowel vents, and as the other poster said, probably went to the charcoal canister via some vacuum switches or solenoids. I used to plug these off too, till I discovered on one of my vehicles, this made it hard to start in the summertime. It acted like it was flooded and required alot of cranking to get it to start. I don't remember how I stumbled on to this, but I found leaving the bowel vent open got rid of the hard starting, even in the hottest weather. But that's when I found out with the hose off, if you hit the brakes real hard, fuel would slosh out of the pipe. So I put a short piece of hose on the pipe that curled upward and it seems to work ok.

 

probably bowel vents

BOWEL vents? Like that little puckered thing?:-staun

 

Does anyone know how to do away with the variable venturi (junk) carb on my 83 351w??...would be nice to get it running..its in great shape otherwise..thanks!!!

 

You could go to summit racing or jegs and get a 4bbl carb and manifold. Or go to the junkyard and get a mtorcraft 2bbl and 2bbl intake from another vehicle.

 

AAARGGGHHH!

The crank case has nothing to do with the fuel system!

A basic PCV system has a check valve, to prevent back-fires from lighting up your crank case gasses. It draws the gasses in the block into the manifold at the carb base (primary vaccuum source).

The Charcoal Canister stores fuel vapor, and it ALSO needs a primary vaccuum source, thus the connection. But you need to understand what is going on to make sense out of it all - under certain conditions the charcoal cannister is allowed to purge the vapors it has stored into that (already mentioned twice) Primary Vac Source (your intake).

But to avoid confusion, you should think of them as being completely seperate systems, that get the vacuum/intake access from the same connection.

I hope like hell this makes sence to you out there.

It's better to know WHY it is, than just WHERE TO PLUG IN HOSES.

So consider the 1/4 inch carb base connection to be just that - a vac source.

Different systems use them. Keep them apart in your mind.

(I bugged, on this concept the other night, I hope what I have said here is helpful)