1978 K10 w/ a SBC350 - Vacuum Lines Setup and Dirty Fuel

[emd802]

I recently received a 1978 K10 4X4 on trade for an old 4-wheeler. The frame, suspension, and drivetrain has little-to-no rust, however, the body is pretty shot (floors practically gone, rust in the fender wells, etc.). The guy that traded it to me said his father used it as a daily driver, but it did run a little rough initially after cranking (but smoothed out after warming up).


It has a 4-barrel quadrajet that I assume came stock with the 350 that’s in it. I noticed there’s no vacuum line hooked up to the PCV valve, and I had a neighbor walk by and tell me that if the vacuum lines aren’t hooked up correctly, it will always run rough.


Anyways, I was cranking it up every other day or so before I ran it out of gas sitting in the driveway. Put 5 gallons of some fresh gas in it and started it up. It turned over, but not before violently backfiring and shutting off. After that, I could not get it to turn over.


I have a coworker who says I should just replace the fuel filter and try it again (and maybe add some B12 fuel treatment into the tank). I have another who thinks I shouldn’t try again until I’ve had the carb rebuilt (which is a more time-consuming/expensive option depending on whether I can do it myself).


What should my next step in tackling this issue? Also, I need to know which way my vacuum lines should go? I’ve seen some diagrams on the Autozone website but cannot pinpoint which one is mine (There’s like 3 different kinds for the 1978 350’s).


I want to keep the truck and get it to daily driver status, but there’s a lot of stuff I have to tackle with this motor first. Any info would be appreciated. Be in mind, I am relatively new to this (usually work on 2-stroke mx motors) so if it sounds like I don’t know what I’m talking about, you’re probably right.


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[Obwonkonobe]

Too little advance unless it’s a tooth off, rotate it a little bit counter clockwise

 

[dvdswan]

Not that it matters, the brake booster usually connects to the port on the back of the carb. In the last picture, where the short hose has the bolt in it, that is usually connected to the vacuum advance on the distributor. (In the picture above the last one, there is a blue clamp at the bottom of the picture, that holds the metal tube that would have short hoses on it to connect the carb to the distributor.)

In the 2nd to last picture, in the linkage of the vacuum for the choke, it looks like a tube that comes out which would have been vacuum to go to the air cleaner to open the port that needs to be plugged.

Aside from that, all others should be plugged. That's how my 78 was set up. If you have an auto tranny they you may need one for the modulator or something. I don't remember, I don't own automatics.

edit: since it doesn't have the correct bolts on the carb, I would pull the carb off and replace the base gasket. The PVC would connect to the air cleaner so its not an issue running with it like it is.

another edit: re-route your spark plug wires so they are not touching each other or lying on metal. They could cause an arc and cause misses.

 

[emd802]

Yes, it is an automatic. Ok, so I need one to go to my vacuum advance on the distributor and my air cleaner, and other than that all others should be plugged? Also, what about the one that's coming from my brake booster? (I can't seem to find that set up anywhere in the diagrams). Yes I plan on re-running all of the spark plug wires.

 

[dvdswan]

It looks like you have one on vacuum advance already. I was just letting you know where my 78 connections were.

Get the carb number off of it, that way you can find all the correct connections on it. With all the ports on that one it may have been from a newer year with more emissions bs on it.

 

[idahovette]

Replace that short piece of fuel line, If it is a bad inside as the outside looks you may be trying to burn rubber. The positive crankcase ventilation usually hooks to a vacuum port on the carb(where your booster is)

 

[dvdswan]

Replace that short piece of fuel line, If it is a bad inside as the outside looks you may be trying to burn rubber. The positive crankcase ventilation usually hooks to a vacuum port on the carb(where your booster is)

That line looks like it just long enough to connect to the PVC too. Something borrowed?

 

[idahovette]

That line looks like it just long enough to connect to the PVC too. Something borrowed?

Maybe, P.O.s do some weird stuff!!

 

[Craig 85]

Based on what on your truck, this looks like the most appropriate 1978 SBC diagram from Autozone.

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[75gmck25]

Stock vacuum line configuration on carburetor should be:
- Threaded fitting on the back of Quadrajet, with a hard steel pipe attached to it. The pipe curves up around the throttle bracket and toward the brake booster, and then the rubber line to the booster is attached to it.

- Large 3/8" fitting with a nipple on the front of the carburetor. Rubber line from there over to the PCV valve in the driver's side valve cover.
The other valve cover should have breather fitting that is used to pull air into the crankcase. Stock configuration was a rubber line connecting to the side of the air cleaner to pull in fresh air, but you could swap in a filtered breather cap.

- One of the small fittings on the lower front of the carburetor is usually connected to the vacuum advance on the distributor., although it looks like they moved yours to the intake manifold port. I prefer manifold vacuum (always on), but the original line may have been connected to ported vacuum (only has vacuum when throttle plates are above idle)

- There may be other vacuum fittings that are used for the hot air or electric choke. In most cases you can just leave them connected or cap them for now. Just don't leave any ports open. For example, the small line curving from the carburetor over to the passenger side of the carburetor is to the choke pull-off. This draws vacuum to slowly pull the choke to a part-open position after the engine starts, so you don't run too rich after start-up. Testing of a pull-off usually includes measuring the number of seconds it take to pull the plate away from full choke.

There is also a vacuum tree screwed into the rear of the intake manifold, on a flat spot near the carburetor base. From this tree you may have a vacuum line to the HVAC canistor under the hood, Air cleaner vacuum door, cruise control, emissions controls, or other accessories.

Bruce

 

[olnick]

Pull the dist cap and check where the rotor is pointing! the back fire might have caused it to jump time on the timing gears/chain? with the crank at TDC the rotor should point to EITHER #1 OR #6 if anywhere between pull the front cover to check the gears/chain for proper timing

Olnick