Help with Carb on computer truck (now wont start at all)

[Pinger]

On the subject of the power problem, have you checked to see if the secondaries are opening at all? It sounds a lot like you are running just on the primary bores, or have a very gradual and sluggish secondary. That would make poor power and response when you floor it, but wouldn't necessarily pop or sputter because the air/fuel is still correct, you just don't have enough of either to make for good acceleration because you are effectively running a small two barrel carb. .

That would be true if the same main jet(s) serve primary and secondary chokes. If the primaries have main jets unique to them, then if the secondaries don't open the air flow through the primaries will be much higher than intended but the (primary) main jets won't be big enough to keep up.
Alternatively, once the airflow limit of the primaries is reached the airflow is 'choked' and if the point of fuel entry is downstream it will be subjected to significant vacuum and if the main jet can flow enough, the mixture will go rich but probably un-noticed as the principle symptom is lack of power due to being starved of air.

Does the carb in question have emulsion tubes?

 

[SAATR]

If you have an auto and no MAF, your trans may not be long for this world. It needs TPS and


So the transfer slots causing the carb to draw off the main circuit deal must be a factor in most carbs? First I heard of it was with the qjet and it's tiny primaries needing a certain amount of bypass air to keep the blades shut enough to stay out of the slots. Then I read more and hear it's a factor with certain Holleys too. Now the Edelbrock. Unless it's a universal characteristic of a carb hitting any ported vacuum slot?

I was incorrect in saying that the transfer slots are pulling off of the main circuit. They are still pulling fuel from the idle circuit, but bypass the idle mixture control screw ports to allow additional fuel to smooth the transition from the idle circuit to the primary main circuit. The gist of my statement is still the same, in that the transfer slots are bypassing the idle screws, so that the idle screws are not in sole control of idle fuel supply. So far as I'm aware, this is a near universal feature.

That would be true if the same main jet(s) serve primary and secondary chokes. If the primaries have main jets unique to them, then if the secondaries don't open the air flow through the primaries will be much higher than intended but the (primary) main jets won't be big enough to keep up.
Alternatively, once the airflow limit of the primaries is reached the airflow is 'choked' and if the point of fuel entry is downstream it will be subjected to significant vacuum and if the main jet can flow enough, the mixture will go rich but probably un-noticed as the principle symptom is lack of power due to being starved of air.

Does the carb in question have emulsion tubes?

Edelbrock, Carter, Quadrajet and Dualjet (2 barrel variant of the Q-Jet) all use metering rods to turn the primary jets into a variable orifice with fuel metering based on manifold vacuum. As long as the rod/jet/spring combination is tuned correctly for the airflow capability of the primary venturies, you won't get a lean or rich condition, just a huge throttling losses and a lack of power. A vacuum gauge on the manifold would confirm whether or not this is happening at wide open throttle. If the secondaries are opening, then the problem is elsewhere, and all of this is moot.

 

[TacosnBeer]

OMG, my eyes are crossed trying to understand the bowels of the carb and how it works or doesn't in my case. LOL

When I had the vacuum gauge on the manifold it idled at 15. When I revved it and it cut out/bogged it dropped to 4. I didn't hit it hard just revved it off idle till it bogged. I will try and see if the secondaries are opening. I think they are... didn't check though.

I noticed my regulator clicks too. when I first start it up the pressure gauge bounces around from 5-6.5 then it levels out at 6... while its doing that it clicks really loud.

I am not above ordering a new carb and regulator... I prefer not to throw unneeded money at it but, I want it right and reliable so I can start driving it.

 

[Supercharged111]

I was incorrect in saying that the transfer slots are pulling off of the main circuit. They are still pulling fuel from the idle circuit, but bypass the idle mixture control screw ports to allow additional fuel to smooth the transition from the idle circuit to the primary main circuit. The gist of my statement is still the same, in that the transfer slots are bypassing the idle screws, so that the idle screws are not in sole control of idle fuel supply. So far as I'm aware, this is a near universal feature.



Edelbrock, Carter, Quadrajet and Dualjet (2 barrel variant of the Q-Jet) all use metering rods to turn the primary jets into a variable orifice with fuel metering based on manifold vacuum. As long as the rod/jet/spring combination is tuned correctly for the airflow capability of the primary venturies, you won't get a lean or rich condition, just a huge throttling losses and a lack of power. A vacuum gauge on the manifold would confirm whether or not this is happening at wide open throttle. If the secondaries are opening, then the problem is elsewhere, and all of this is moot.

Is there a general rule of thumb for how far into the transfer slot is OK that works across the board? Or should it be not at all?

 

[SAATR]

OMG, my eyes are crossed trying to understand the bowels of the carb and how it works or doesn't in my case. LOL

When I had the vacuum gauge on the manifold it idled at 15. When I revved it and it cut out/bogged it dropped to 4. I didn't hit it hard just revved it off idle till it bogged. I will try and see if the secondaries are opening. I think they are... didn't check though.

I noticed my regulator clicks too. when I first start it up the pressure gauge bounces around from 5-6.5 then it levels out at 6... while its doing that it clicks really loud.

I am not above ordering a new carb and regulator... I prefer not to throw unneeded money at it but, I want it right and reliable so I can start driving it.

Ok, first things first. Verify that the secondaries are opening when the accelerator is at wide open throttle. You can do this with the engine off. Watch the secondary butterfly shaft as you move the throttle to wide open. The linkage should start opening the butterflies when the primary is at around 60 percent. If it doesn't, then it may be locked out by the choke. If it does, then that takes us to other things.

Second, move the vacuum advance line to the full manifold vacuum port and cap the ported vacuum. This should raise your idle. Back out on the idle speed screw until RPM is back where you want, and retune the idle mixture screws. That SHOULD get you off the transfer slots at idle. There is no disadvantage to running full vacuum advance at idle. Base timing at 12 degrees should be fine for now. Let us know what you find.

Edit: Grab your timing light and a helper. Plug off your vacuum advance and check to see where your timing is at 2000, 2500, and 3000 rpm. Just want to see where your advance curve is and where total timing is set.

Is there a general rule of thumb for how far into the transfer slot is OK that works across the board? Or should it be not at all?

As little as possible while being able to set a stable idle. Big cams can make it difficult or impossible, but that's where drilling and modifying air bleeds comes in to the game. If you can kill the engine by running the screws all the way in, you're generally fine.

 

[TacosnBeer]

Verified, secondaries are opening at about 60% throttle.

Switched the advance line to the right port, adjusted the idle and tried to dial in the left n right screws... still no response. I set them at 1/5 turns out of ***** n giggles.

Verified the timing at 12 deg, took it to 2000 rpm and it went to straight-up - top of the balancer. I only have a dummy tuning light so don't know exactly how far but it was about at 0deg straight upish... the more rpm the more it moves toward the top.

Took it for a drive and it was worse. anything other than easy throttle and it fell on its face and sat there at poop stage if I backed off it eased in but still felt like crap.

Just as FYI - I replaced the vacuum line and checked around the carb with carb cleaner for a gasket leak and she is solid. I also pulled the mixture screws and they arent grooved. There are only 2 ports on the edelbrock and both are either used or capped off.

 

[SAATR]

Verified, secondaries are opening at about 60% throttle.

Switched the advance line to the right port, adjusted the idle and tried to dial in the left n right screws... still no response. I set them at 1/5 turns out of ***** n giggles.

Verified the timing at 12 deg, took it to 2000 rpm and it went to straight-up - top of the balancer. I only have a dummy tuning light so don't know exactly how far but it was about at 0deg straight upish... the more rpm the more it moves toward the top.

Took it for a drive and it was worse. anything other than easy throttle and it fell on its face and sat there at poop stage if I backed off it eased in but still felt like crap.

Just as FYI - I replaced the vacuum line and checked around the carb with carb cleaner for a gasket leak and she is solid. I also pulled the mixture screws and they arent grooved. There are only 2 ports on the edelbrock and both are either used or capped off.

So the mechanical advance is working right, the vacuum can seems to be working right, and performance got worse when you drove it.

Leave everything as is, and back the fuel pressure regulator down to 3psi and retest.

 

[TacosnBeer]

on it!

 

[TacosnBeer]

So the mechanical advance is working right, the vacuum can seems to be working right, and performance got worse when you drove it.

Leave everything as is, and back the fuel pressure regulator down to 3psi and retest.

3psi and it is the same. Bogs out when you rev it. No change.

 

[SAATR]

My only other suggestion is to increase fuel pressure to 9psi and retry. I'm aware that it is more than the needle and seat are capable of handling and it should flood immediately, but it is possible that the pressure gauge is inaccurate. Without a known good gauge to check it against, it would at least prove that you should have more than enough fuel.

If it doesn't flood out, and especially if it runs better, I would question the gauge. If it floods, put fuel back to 6psi, put the vac can back on ported vacuum, reset the idle speed with the screws 1.5 turns out, and see if it runs like it originally did. If it runs like it did before, cap off the PCV and brake booster lines and see if it improves. I'm especially curious about the brake booster. Carburetor is also possible, especially with Edelbrock's recent build quality, but we're trying to eliminate everything else first.