77 C10 350 OEM carburetor question

[TexasRed]

I don't see a picture of anything, so it may be a PCV valve? You might search google for part number FV184 which is the most common PCV valve I believe. The PCV valve should have a 3/8" hose going to the base of the carburetor or perhaps a spacer. Some people "Tee" into the hose for the power brake booster which is at the back of the carburetor (usually). Some people say that's not a good idea.

Some intakes have a port in the intake on I think cylinder #8. I use that one for the brake booster. The problem using that for the PCV valve is because it will cause a lean condition for that cylinder.

A specific diagram may not be truly helpful because you may get to the point that you've got so many modifications that the diagram won't be very close.

[Steppin Razor]

Fixed (I hope)

thanks @Silverminer . didn't see a vacuum diagram in the manual

[TexasRed]

Yes, that's a PCV valve.  That requires a 3/8" hose to a place that provides full time (manifold vacuum). You'll also need a "breather" on the other valve cover that goes to the air cleaner. Is your air cleaner stock?

Edit: is that a manual choke? Do you have it hooked up?

2nd edit: you may only have one 3/8" vacuum connection on that carburetor. It's probably being used by the brake booster.  You also appear to be using ported vacuum for the distributor advance, which is probably not the best way to run vacuum advance, but it's probably not a huge problem.

I don't think either thing is causing the issues you're seeing however.

[Steppin Razor]

Yes, that's a PCV valve.  That requires a 3/8" hose to a place that provides full time (manifold vacuum). You'll also need a "breather" on the other valve cover that goes to the air cleaner. Is your air cleaner stock?

I don't know if it's stock, but it doesn't have a connection to a pcv valve.  It has a blocked off port on the side that looks like a 5/8" hose barb (bigger than the pcv valve) and what I guess is the flame arrestor.  That's it.  No pcv valve runs to it.  The pcv valve on the other valve cover looks like it runs to the distributor cap, but I'll trace it down tomorrow and get more pics.

Edit: is that a manual choke? Do you have it hooked up?

It is.  Hooked up to what?  Sorry, this is my first experience with a carburetor.  Oldest car I've owned prior to this was an 84 Benz diesel station wagon.  Everything else has been fuel injected.

2nd edit: you may only have one 3/8" vacuum connection on that carburetor. It's probably being used by the brake booster.  You also appear to be using ported vacuum for the distributor advance, which is probably not the best way to run vacuum advance, but it's probably not a huge problem.

I don't think either thing is causing the issues you're seeing however.

Honestly, given how it's downing gas since the fuel leak repair, I feel like the first thing is to fix air/fuel, but I haven't figured out how.  The PO actually gave me an instructional cd that came with the carb, but both that and the online manual for the actual model on Holley's page show a different setup than mine has.

[TexasRed]

OK, a little idea on the PCV Valve: It's more of a system of two sides.

One side: The "valve" goes to one valve cover where it sees vacuum from the carburetor/intake. That's the side that provides "vacuum" that sucks blow by gases into the intake to be burned. It also provides a vacuum to the bottom side of the piston rings.

2nd side: A breather goes into the other valve cover. The idea is to separate the two systems so it functions correctly. The breather has a tube that goes into the air cleaner that has a filter or goes through the normal filter. It does NOT go into the valve at all. It's just to provide clean air to the crankcase.

So oily air gets sucked through the valve into the intake and it's replaced by clean air through the breather on the other side.

The manual choke should be connected to the cable in the cab. If the choke is always on, it can cause a lot of gas usage. The choke is a plate on the primary side of the carburetor (the one nearest the radiator). I've only used electric chokes, except on motorcycles, so I'm not sure what the hookup looks like on a holley. I guess the question is, does it work?

The other thing to check is the fuel pressure too, some stock fuel pumps put out over 7 psi which can push past the needle and seat on a holley.

edit: what is the liquid on the intake?

[JohnnyPopper]

Tex is right on.

Fresh air from a separate filter in the air cleaner gets sucked down one bank of push rods, through the oil pan, then up the other bank of push rods to be added to the air/fuel mixture being consumed by the hungry pistons.

The PVC valve, (positive crankcase ventilation) meters the flow so it's not affected too much by the rise and fall of vacuum, i.e. acceleration/deceleration.

Simple enough, right? What a beautiful design!

[Steppin Razor]

Ok, so the disconnected one is the breather and from further reading, looks like maybe there's been some EGR delete and it went to the EGR valve, which went to the intake(?).  There's no cable or anything on the choke, I have no idea what the PO did with that.  Maybe it had an electric one which was also deleted.  So right now, to adjust the choke requires popping the hood and doing it by hand.

I also figured since I had the fuel leak fixed, the fuel level could be too high, but the Holley CD and Holley manual for the carb give instructions that don't reflect the actual carburetor.  This carb has multiple applications, maybe this isn't the GM one.

[TexasRed]

The one in the red circle should be the PCV valve. If you pull it out and shake it, should make a noise.

The EGR valve should have a ported vacuum line, and in fact the quadrajet had a special one that took some throttle opening to start seeing some vacuum. The holley won't have that. So if you do have an EGR valve, the vacuum hose is probably not hooked up to the carburetor, making it nonfunctional unless it stuck open due to carbon.

If the choke is closed when you are driving, it will cause the engine to use a bunch of fuel. I don't think the carburetor was converted to manual from electric because usually once you go electric, you don't go back unless you need it to look somewhat period correct in the cab. It takes different parts to make it electric vs manual. Some people don't use the choke and just feather the throttle until the engine is warmed up.

A lot of the holley float levels can be adjusted externally. Yours cannot. You would need to set it the dry internal way by pulling the bowls. You'll spill the gas out of them when you do, so be aware. https://documents.holley.com/techlibrary_adjusting_your_carburetor.pdf

I would also check the fuel pressure because too much can still push past the needle and seat.

Some other reading guides: http://bob2000.com/carb.htm
If you can pull your list number off the carb, holley may have some information that is specific to your carburetor.

[JohnnyPopper]

In your last pic, it shows a 3/8 hose coming from under the front of the carb.

Where does the other end go? That might be your PVC intake hose.

[Steppin Razor]

Thanks.  There's no cable to the choke, and no knob or anything on the dash.  It has new electrical done in the cab, which seems to have some gremlins (wipers randomly go off on start up, intermittent doesn't work, dome light doesn't always work) so I thought maybe there was an electric choke originally.  In any case, looks like I'll have to figure out a cable.  An aftermarket radio was installed so I can use one of the old spots for a knob.

I believe there was once an EGR valve in between the pcv valve/breather and the intake based on what I saw in the manuals that are linked.  I don't see any egr equipment on it, and since TX doesn't require emissions for a vehicle this old, a delete is common.

@Johnny Popper, that is a vacuum line I believe.  It goes to some little canister thing mounted on the firewall at the top passenger side corner.

I think next I'll fiddle with the choke, check vacuum, and pull spark plugs to take a look.  Fix a cable, then if I still have problems, take a look at the ignition coil.

[JohnnyPopper]

That is most likely the hose for the PVC valve. The Canister on the Firewall is a booster for your AC/Heater controls. It usually is supplied Vacuum from the port behind your carb, same as supplies to your Power brakes if you have them.

Get your PVC circuit squared away, it's not a bad thing.

[Chevygold]

My other car is a 70 Corvette with 350 and I went through a similar experience with it which turned out to be a vacuum leak due to a carb to manifold mismatch, during my search for a solution I rebuilt the Holley which it came to me with but no cure, the problem was solved when I fitted a Brawler carb which went straight on and cured the vacuum leak which I only discovered after removing the carb and seeing the mismatch on the gasket.
The Holley was dead easy to rebuild everything was in the kit including comprehensive instructionsto  take you through the process step by step.
This Holley is now on my C10 after dirt in the fuel blocked up the idle system in the Edelbrock which it came to me with and it's finally running good, I had to make up a throttle linkage to get the Holley to run and mount a kick down switch after swapping out the TH350 for a TH400, the TH350 would only drive in reverse but that's another story!
Hope you get yours sorted.
Graham

[TexasRed]

Harbor Freight sells a vacuum tester that you'll need to adapt some to use it for reading fuel pressure. It reads it but you'll need to find a good way to get it in the line. The tester is setup for reading the fuel pressure level that the stock mechanical puts out.

https://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html

I'd google for a 20% off coupon. Hopefully there's a HF near you.

I'd check the fuel pressure, vacuum with it. The choke, as long as it's open when the engine is warmed up shouldn't cause an issue. For driving it some, yes, you would want to find an appropriate solution.

It could also be as Chevygold states a mismatch between the carburetor and adapter or adapter to manifold. There is a metal plate that can be purchased if there is a mismatch. Older holleys like the 4010 had that problem.

[Steppin Razor]

Ok, so I bought the vacuum/fuel pressure tester, about to go test.  Yesterday and today, it stalled out at idle so I had to keep my foot on the accelerator and left foot brake to keep it running at red lights.  And it stalled twice while turning at speed. It also happens when warmed up, less so when cold. Parked on a hill, it idles fine.  I'm also sending half my fuel unburned through the tailpipe.  Also, there is another fuel drip.  This one is coming from the spot in this pic between the o and b in photobucket





Edit:  Ran vacuum test, it's at 18in/Hg at first, but over time it dropped to 15

[TexasRed]

That leak may be the rear float bowl leaking. May want to see if you can snug up those bolts a little but not too tight. It doesn't take much to strip the threads in the body.

It may also be leaking a little because the fuel pump is pushing fuel past the needle. Did you get a chance to figure a way to hook up the pressure gage on the 3/8" line?

Extra fuel pressure may be causing the vacuum drop at idle.