Edelbrock 1405 carb running rich

[iamtherealJayy]

I have a 1978 Chevrolet K10 with what appears a bone stock 350. It originally has a quadrajet carb that severely needed rebuilt. I bought the truck non running with the carb sitting inside the truck so it might have not even been original. I had to set the timing to tdc because it wouldn’t run all it did was backfire out of carb. Got that resolved by resetting the timing but the carb leaked fuel and was just worn out. My buddy has an el Camino with a 350 and he decided to get a new carb since he had spare cash(same carb just new) and said I could have his old one. I jumped on it got it all setup truck starts decent it has sat for over two weeks and I gave the throttle one pump for good luck and it starts. But it runs rich in my opinion. If you give it a quick throttle it sounds like it takes a quick inhale but it bogs, I’m not sure if this is timing or the carb. I can set the timing on my other trucks but this one doesn’t have a tab on the timing chain cover? So I can’t dial it in to the 8-10° I’d like to be around. I’m not sure if the running rich and bogging is timing or the carb. The air fuel screws on the carb are at about 2-1/4 turns out from being the whole way in. I advanced the timing slightly and hit the throttle and it popped from exhaust(backfire I assume?) The carb is manual choke but it’s not hooked up so it’s just always open but I have a manual choke cable and tachometer on the way.
Edit: I set the carb to 2-1/4 turns based off a vacuum gauge hooked to a port on the carb and tried to get the highest I could get on the gauge.

 

[fast 99]

When the throttle is opened it changes fuel flow out of the idle circuit. If a rich condition under higher RPM is suspect, adjusting the idle circuit will do little to nothing to resolve that. Do you know if either advance works? A backfire like that is usually caused by either a lean condition, misfire or valve train problem, such as a broken valve spring or flat cam. Get a good base line on the tune up. Look at the plugs and wires [remove all the wires at the cap one at a time inspect for corrosion] check fuel pressure, check rotor for burn through near center [if HEI] carbon tracking, ect. Just do a good visual check. Also check for steady vacuum and vacuum leaks.

Modifying this post, these suggestions are for diagnosing a backfire into the intake not exhaust.

 

[iamtherealJayy]

Plug/wires are new not much run time on them. The vacuum gauge reads steady on manifold vacuum and lowers vacuum under throttle and higher when you let off throttle then comes back to steady. Should be no vacuum leaks pcv, vacuum advance(ported), and the brake booster are only vacuum lines hooked to carb everything else has been capped(manifold vacuum has a gauge currently but have a cap for it). The truck has a quadrajet to edelbrock 4 barrel carb plate with new gaskets. Truck also has an egr block off plate if that matters.

 

[SirRobyn0]

Ok I'd strong suggest you solve that no timing tab situation so you can set the timing properly. Yes, popping on letting off the throttle at the exhaust is a sign of being advanced, but that might not be where the initial is set at. You might wanna pop the cap and rotor off and check the advance springs and weights.

You should be in the ball park for the mixture screws, but that's a used carb, is it stock inside? does it have bigger jets? Did the el Camino run rich?

Is the gas in your truck ancient? I've found at the shop we have resurrected vehicles that have sat, and they smell stinky, it's not exactly the same as being over rich, but similar smelly exhaust. Seems like gas over 6 mnts old will produce this smell getting worse the older it is.

Regardless fix that missing timing tab, you get aftermarket ones for the 350 easy.

 

[iamtherealJayy]

You see id get those tabs but I’d still have to just set it at tdc and make a mark somewhere and go from there because no harmonic balancer and timing tab are going to match unless they’re the original pair that went together. The gas isn’t old. Brand new tank new soft lines new pump and new in-line filter. The carb is a stock edelbrock 1405 manual choke carburetor. I couldn’t tell you if the elcamino ran rich or not I only saw it in person twice. But it ran fine, he never daily drove it it was kinda a weekend driver for cruising. I believe the distrivutor is an hei unit since it’s got the coil built in on top, correct? That’s why I’m getting a tachometer since I noticed it’s got a newer style distributor like my ‘87. It looked fairly good last time I was in it 6 months ago or so, but I can check again and make sure the advance moves freely and the rotor looks fine along with all the contact points in the distributor cap.

 

[SirRobyn0]

You see id get those tabs but I’d still have to just set it at tdc and make a mark somewhere and go from there because no harmonic balancer and timing tab are going to match unless they’re the original pair that went together. The gas isn’t old. Brand new tank new soft lines new pump and new in-line filter. The carb is a stock edelbrock 1405 manual choke carburetor. I couldn’t tell you if the elcamino ran rich or not I only saw it in person twice. But it ran fine, he never daily drove it it was kinda a weekend driver for cruising. I believe the distrivutor is an hei unit since it’s got the coil built in on top, correct? That’s why I’m getting a tachometer since I noticed it’s got a newer style distributor like my ‘87. It looked fairly good last time I was in it 6 months ago or so, but I can check again and make sure the advance moves freely and the rotor looks fine along with all the contact points in the distributor cap.

If you can figure out which balancer you have (there are only two factory marks) then you can figure out which tab to order. I'm not smokin' anything on this I've done it a number of times at the shop, for various 350's that came in missing the tab. You can also buy matched balancer and tab. I doubt the distributor would go that bad in 6 mnts. Yes, that's an HEI unit. The only other thing is if the fuel pressure is to high it can push past the float. Edlebrocks don't like to much pressure, 6PSI MAX, 4 to 5 is what most guys run. It's a used carb, so perhaps it is as simple as the carb needs to be rebuilt.

Check the vacuum readings, should be 17 - 21 at idle, down to 15 is ok, but anything lower than that is a issue. The needle should be steady at idle and not fluctuate. But really to get accurate vacuum readings you need to be able to set the timing properly with a light first, since you can't I'd still check vacuum, it still should be steady, but with a questionable timing set you may get a little high or lower than normal readings.

What does the inside of the tail pipe look like. Is it tan in color, is it black, if it's black is it wet and oily, or dry?

You probably should pull the plugs, and see if they are black, if it's rich they'll be black. don't pull just one yank them all and while your in there run a compression test, to find out what the health is like of the engine. If you have low compression you'll never get it to run or smell correctly. (I assumed that you had already set the idle mixture screws), if not please say something so we can go over that.

I'm not trying to be a jerk in throwing all this stuff at you. At the shop we do a fair bit of work on older rigs and often have one or two squares in there at a time, and sometimes you just got to diagnose, and make sure the internals of the engine are up to snuff. It does not help that we cannot see or smell it with you, but that's just how it is on the internet.

If you want something easy to just try, you could turn each mixture screw in 1/4 or turn (in is leaner out is richer btw), that will be a fair bit leaner, if that doesn't seem to be enough go another 1/4 turn in on both screws, if that seems like to much (makes it run rough go out a 1/8 turn on both screws.

 

[SirRobyn0]

I should also add that I assumed you'd already set the idle mixture on the carb with the engine running, either using a vacuum gauge or by RPM or feel. If not then that maybe a good place to start, but I still think you should check to see if it is actually running rich first since you are not sure if it's in the timing or carb.

 

[iamtherealJayy]

I did use a vacuum gauge to to set the screws but I honestly didn’t pay attention to the number it was at I was going for highest on the gauge, it was in the green “normal engine” area. And vacuum would drop with throttle and if you just let go of the throttle the vacuum would shoot up then return back to where it was, on my gauge it wasn’t bouncing around just idling. I can check the vacuum later, but can I check it on a cold engine or will the results be different? It’s hard to let it run long enough to get warm with how it’s running. I can get photos later of the exhaust(currently a straight pipe exiting under bed, I’m redoing the exhaust and trying to find a good muffler choice), carb, distributor, and anything else that might be useful.

 

[SirRobyn0]

I did use a vacuum gauge to to set the screws but I honestly didn’t pay attention to the number it was at I was going for highest on the gauge, it was in the green “normal engine” area. And vacuum would drop with throttle and if you just let go of the throttle the vacuum would shoot up then return back to where it was, on my gauge it wasn’t bouncing around just idling. I can check the vacuum later, but can I check it on a cold engine or will the results be different? It’s hard to let it run long enough to get warm with how it’s running. I can get photos later of the exhaust(currently a straight pipe exiting under bed, I’m redoing the exhaust and trying to find a good muffler choice), carb, distributor, and anything else that might be useful.

Warm is best, but if it's hard to warm it up cold is fine. So if you set the mixture with a vac gauge you could just try going a 1/8 or 1/4 turn in on BOTH screws and see if that solves the rich smell. But again check plugs, check tail pipe to confirm it is actually running rich.

 

[iamtherealJayy]

The screws are equal currently, and the exhaust blows black smoke, not as much as a diesel, but black smoke. Not blue smoke if it was burning oil. Running finger inside exhaust left a black coating on my finger. I’m taking pictures to send right now.

 

[iamtherealJayy]

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[iamtherealJayy]

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[iamtherealJayy]

Startup and exhaust:

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Vacuum gauge 16 in hg:

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Exhaust idling:

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Bog on quick acceleration:

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[iamtherealJayy]

Half of my photos are “awaiting moderator approval”

 

[SirRobyn0]

It's ok on the missing pictures. Thanks for the info. When does it blow black, at idle? Steady cruise RPM? Acceleration? Letting of the throttle? I'm really starting to think it's an internal carb problem and it's going to need a rebuild, but would be good to know when it is occurring. Previously I thought or maybe assumed it was rich at idle and you were smelling it not seeing black.

That pipe definitely looks rich, doesn't look like oil to me so that's good news.