'77 350 running very poorly

[J Lee]

So one day last week I was running down the highway in my 77 K20 at 55 or so and out of nowhere the engine fell on its face power wise. I wasn't too far from home so I turned around at the next opportunity and noticed that it seemed to run fine other than in high gear where it would lose all power unless I was very easy with the throttle. Got the truck back home shut it off and left it as I was running late already. The next day I popped the hood and found the Mr gasket fuel filter absolutely full of trash and rust looking particles. I took it apart cleaned and reinstalled it and drove it around town running errands the rest of the afternoon without issue. The next morning I decided to drive it to work and didn't make it a mile down the road and it fell on its face again. Once again got it back home jumped in a different truck and went to work. This time there was no trash in the filter so I figured some trash had made it to the carb at the same time I pulled the plugs and gave them a good cleaning although nothing looked really abnormal. I changed carbs to a 600 Holley I had on the shelf and the problem still persists. I would rather not just start changing parts but diagnose where the trouble is just not sure where to start. Any and all help is appreciated.

As an addendum in the midst of all this I did crank the truck and ease it across the field behind the house at which point it sounded like it was running on 4-6 cylinders.

Jeff

[GASoline71]

Sounds like you got rust and crud in your tank and/or fuel lines.

Gary

[J Lee]

Yes, not real happy about finding that much crap in the filter just wondering did it somehow cause the issue or just a coincidence?

[68gmsee]

One thing you can try is to go to the parts store and purchase 2 or 3 feet of fuel hose (the same size as the fuel pump intake hose).

-Use a one gallon container of fresh, known, good fuel and place it under the fuel pump.
-Remove the fuel supply hose from fuel pump and replace with new hose.
-Place in the gas container.

If truck runs okay the fuel in the tank is contaminated or fuel lines are restricted.

If it doesn't it could be fuel pump or junk still in the line and carb.

To test the fuel pump, remove line from carb and place in a quart container or similar. Pump should pump at least a pint of fuel in less than 30 seconds.

[J Lee]

Thanks 68gmsee I'll give that a try next chance I get to work on it.

[J Lee]

Finally I got a little time to mess with the truck again. I pulled the fuel line off the carb and put it in this pint jar, this is the amount of gas I got in 10 seconds.


Jeff

[J Lee]

While I'm at it does the vacuum hoses appear to be in the correct place on the carb?

[Rickysnickers]

I'm not really familiar with Holley carbs, but isn't the vacuum line for the distributor supposed to be attached to a vacuum port under the throttle blades? It appears you have the PVC line hooked to your brake booster too. There should be another large port at the firewall end of the carb, on the bottom, for your brake booster.

[Ironangel]

According to this image, you should be alright. Hopefully you have a PCV valve piped in that we cant see from this angle? And the black blinker fluid line is missing from your carb...?

[Ironangel]

See that plug in the manifold right in front of the distributor? Use that for your booster vacuum and the port on the carb can supply vacuum for the PCV that should locate right there on that right side valve cover. You already have the left valve cover vented. If that's an automatic transmission, might want to check the modulator vacuum line and connections for leaks or cracks. I'm seeing a black hose in the image and red caps in your pic, whats up with that? Performance mod?

[nonstop]

Agreed about the vacuum lines, but wanted to ask, how are you running the choke?

[cadillac_al]

Why is the gas so yellow? Ours is almost clear up north. Does this truck still have a catalytic on it? Clogged cats will feel like lack of fuel too.

[68gmsee]

Originally Posted by cadillac_al

Why is the gas so yellow? Ours is almost clear up north. Does this truck still have a catalytic on it? Clogged cats will feel like lack of fuel too.

Fuel takes on a different hue depending on chemicals added to it, including ethanol amount. Also, states have different requirements for amounts and types of additives in summer and in the winter time.

However, that does not mean the fuel is not contaminated. I usually change brands if I suspect that I have gotten some bad fuel. Doesn't happen often but it has happened.

[Ironangel]

Originally Posted by nonstop

Agreed about the vacuum lines, but wanted to ask, how are you running the choke?

If your asking me, I run a divorced choke on both my 72's and they both have Rochester Quadrajet's, different breed of cats. Nothing wrong with the electric choke systems shown in the pic, the trick is knowing how to set them. Here's a link I found to get you started, Google is your friend... http://forums.holley.com/entry.php?4...rel-Carburetor

[nonstop]

Originally Posted by Ironangel

If your asking me, I run a divorced choke on both my 72's and they both have Rochester Quadrajet's, different breed of cats. Nothing wrong with the electric choke systems shown in the pic, the trick is knowing how to set them. Here's a link I found to get you started, Google is your friend... http://forums.holley.com/entry.php?4...rel-Carburetor

I was asking the OP, since there is only one wire attached to the choke, but the divorced choke set up is still there, so I was wondering which he was using or planning to use.

[Ironangel]

Originally Posted by nonstop

I was asking the OP, since there is only one wire attached to the choke, but the divorced choke set up is still there, so I was wondering which he was using or planning to use.

The pic I posted doesn't show the wire but does show where the short wire ground supposedly attaches to the vacuum dashpot screw. There are two spade terminals on the choke housing, one positive (right) and the ground (left). For some reason the ground wire itself isn't shown. As far as the divorced choke coil shown in the pic, I think that's a relic left over from the factory Quadrajet that was once there before the Holly took it's place? That appears to be a cast iron factory intake with the choke coil intact without the cover. I dont think that's an option with a Holly carb.

[J Lee]

Sorry it's taken me so long to get back to this. I've been busy and haven't had time to mess with the truck lately. This past week I did get back to it and it had gone from running crappy to not running at all. To make a long story short I changed the dist. cap, wires, and plugs and am now back to the original problem of an OK idle but falls on its face with a miss under load. I did limp it to the gas station and put some fresh gas in. When I returned home I noticed the breather on the left cylinder bank ( visible in the picture on post 7) was soaked in oil as was the valve cover behind it. I will be taking it to a mechanic in the coming weeks as valve train issues (which I now suspect it is) are beyond my capabilities. Thank you for the help in trying to figure this out.

To answer questions asked above:
I'm not sure why the gas is that color. The truck hasn't been used much lately and was low on gas so something in the tank discolored it maybe?

The choke isn't hooked up on it.

I don't think it ever had a cat on it. For sure it doesn't now.

[garyd1961]

If the electric choke isn't hooked up how does the choke plate open?

[GASoline71]

If you're breather is puking oil... you don't have a functioning PCV system. You NEED to have a functioning PCV system to help alleviate pressure in the crankcase.

Gary

[J Lee]

Originally Posted by garyd1961

If the electric choke isn't hooked up how does the choke plate open?

It stays open all the time. Honestly I would prefer it didn't have the choke system at all.

Originally Posted by GASoline71

If you're breather is puking oil... you don't have a functioning PCV system. You NEED to have a functioning PCV system to help alleviate pressure in the crankcase.

Forgive me for being dumb, how does the pcv function so that it relieves pressure whereas an open breather won't?

Gary

[garyd1961]

In your picture your choke is closed.

[68post]

Is the rest of the engine original ?

[J Lee]

Yes the rest is bone stock. It has 24,000 original miles. Although many of those are likely drive it like you stole it miles.