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

[TacosnBeer]

Ok, shot the timing and she is sitting at 12deg before TDC (idles and sounds happy there) 750-800rpm at idle. Adjusted the carb but... weirdly I could screw in both screws and she still ran... it didn't die or stumble. I set them both at 1.5 turns out and used a vacuum gauge in the right (manifold pressure) port and a stable 15 at idle. I rev it easy and she revs, it crack it hard and she cuts out then goes.. no pops or backfire just sounds like it almost shuts off... just like when driving.

then took it for a drive.

It sounds ok and drives ok unless I gas it hard and she still falls on its face still. It feels like the power is there but it just cuts out for a bit then eases back in even if I keep my foot in it hard. Its not popping studdering or smoking it just cuts out.

Oh and she does have both 02 sensors in there still (I previously said she didn't) - I don't have a way to read any of it.

Also... I regapped the plugs. they were at .055 and I put them at .035 ... It is not the of motor and it is carbed not injected so, I assume old-school carbed SBCs were .035 so that made sense to me. Based on last time I drove it, that didn't seem to make a difference.

It feels like it wants to go.. the power is there, it just immediately cuts out (not peter out)

 

[Supercharged111]

When it cuts out, it doesn't come back a second later? The screws don't affect anything past an idle. If it's cutting out and not puking fuel out the exhaust it's gotta be running out of gas. Did you ever put eyes on what size jets you have on both sides and needle sizes? That one that was stuck down will make it lean on one side when you crack on it.

Also, was the timing 12 degrees with the vacuum line hooked up? What was total?

 

[TacosnBeer]

When it cuts out, it doesn't come back a second later? The screws don't affect anything past an idle. If it's cutting out and not puking fuel out the exhaust it's gotta be running out of gas. Did you ever put eyes on what size jets you have on both sides and needle sizes? That one that was stuck down will make it lean on one side when you crack on it.

Also, was the timing 12 degrees with the vacuum line hooked up? What was total?

Yes, 12deg was with vacuum line from dizzy disconnected and capped on the carb.

I floor it and its feels like the motor shuts off instantly... It stays like that for a few seconds then it eases back on the power. When I change the tranny from D (w/overdrive) to 3 it helps a bit and isn't as drastic but, it still does it. Has more power there due to the lower gearing I guess.

As for the guts of the carb, no clue. I assume it's a bone stock Edelbrock 650. It had a 750 on it before and did the same thing for the PO.

 

[Pinger]

I floor it and its feels like the motor shuts off instantly... It stays like that for a few seconds then it eases back on the power. .

How quickly are you 'flooring' it? Stamping on the pedal? Does it behave differently if you ease gently into the pedal?

And when driving and encountering load and it loses power - is that at the throttle opening you were driving (cruising) with, opening it slightly, opening it fully, and if either of the last two - again, how quickly?

 

[Supercharged111]

You beat me to it pinger. It's sounding like the accelerator pump may be at least partly to blame, but we need to ask the questions just right and make sure we're all using the same words the same way. When the power comes back, does it hit like you'd expect it to or is it still on the gutless side? Another thing, you should be able to feel, with your foot, the point at which it begins to open the secondaries. Pay close attention as to whether that much throttle begins to make things better or worse.

 

[TacosnBeer]

it stumbles like it "total shut off" (rpm stops wherever I am when I hit the pedal - if I am at 2500rpm and I floor it, it stalls and sits at 2500rpm) then eases back in... its not like a big hit when it comes back in. I can feel there is power but, it's just not all at once when it comes back. more throttle induces it to cut out or stay cut out longer. No popping pinging or backfire.

 

[TacosnBeer]

How quickly are you 'flooring' it? Stamping on the pedal? Does it behave differently if you ease gently into the pedal?

And when driving and encountering load and it loses power - is that at the throttle opening you were driving (cruising) with, opening it slightly, opening it fully, and if either of the last two - again, how quickly?

If I ease into it, it is a bit better but still stumbles. There is a little difference between D and 3 on the tranny too but, not sure if that is gearing that makes it feel better/more power. When driving under load (uphill) it has a sputter or miss... not a total cut out like when I just floor it.

Hope that helps. Do you think its the carb? For some reason to me, I am thinking it could be something electronic? I am not sure though. Never dealt with an issue like this before with a standard SBC 350. Could it be something with the computer and the tranny since the HEI is running independently of the computer which is controlling the transmission? It does shift funny sometimes too.

One thing to add, there is a lot of black wet **** coming out of the exhaust. Possible unburned fuel> it doesn't smell like gas tho.

 

[SAATR]

First, it sounds like you have too much of the transfer slots exposed in the primary bore, causing the engine to idle off of the main fuel circuit instead of the idle circuit. Back out on the idle speed screw on the throttle linkage to close the primary butterflies, which should put you back on the idle circuit and make the idle mixture screws a lot more responsive. Once you do that, retune the idle and initial timing. If that doesn't make the idle screws work properly, ie you can make the idle rough or shut the engine down by turning them in, then that may be indicative of a problem with the carb.

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. If memory serves, the choke linkage locks out the secondaries until the choke completely opens. If the choke linkage is misadjusted or binding, it will prevent the secondaries from ever opening. Also, if the secondary air door spring is set too tight, it may barely open or not open at all, though I doubt that is the problem.

 

[Erik the Awful]

I can use the gauge port as a return line on my current Holley regulator. Just have to set it with the gauge then swap the return line in its place so, I will hit that later since it's doesn't seem to be a major issue contributing to the current problem.

Yeah, it doesn't work that way. I know because I looked into that same thing when the TBI couldn't feed my motor and I briefly considered swapping my Carter 650 onto it.
View media item 32145
Also, back in post #10: "Check your accelerator pump shot."

SAATR's right with the recommendation on resetting and adjusting your carburetor. Edelbrock has good instructions on their site somewhere for adjusting from scratch. I bought their "tuning kit" that has a handful of jets, and it's not really worth it. Buy a set of tiny drillbits, a tiny drill collet, and a handful of screws with the same thread size as your jets. Drill a hundred of your own jets cheaper than you can buy ten sets.

 

[Supercharged111]

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

First, it sounds like you have too much of the transfer slots exposed in the primary bore, causing the engine to idle off of the main fuel circuit instead of the idle circuit. Back out on the idle speed screw on the throttle linkage to close the primary butterflies, which should put you back on the idle circuit and make the idle mixture screws a lot more responsive. Once you do that, retune the idle and initial timing. If that doesn't make the idle screws work properly, ie you can make the idle rough or shut the engine down by turning them in, then that may be indicative of a problem with the carb.

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. If memory serves, the choke linkage locks out the secondaries until the choke completely opens. If the choke linkage is misadjusted or binding, it will prevent the secondaries from ever opening. Also, if the secondary air door spring is set too tight, it may barely open or not open at all, though I doubt that is the problem.

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?