SBC - sputters/stumbles at speed.

[fear_nothing]

My 1st gen, with plain ole SBC is bogging down nicely at 30/40 ish MPH.
-idles like a champ
-will occasional sputter on takeoff

-Messed around w/ the electric choke
-same with the mixture screws

The carb has been rebuilt, the wires/plugs seem good. I've snugged up all the bolts on the headers.

The carb is a Edelbrock 1400 series, rebuilt about 5 months ago.

What else should I be checking?

-Timing?
-Vacuum Leak?

 

[paratrooper307]

Timing is a likely candidate. Did you use a vacuum gauge when you adjusted the mixture screws? Vacuum leaks are a possibility, but they usually are more problematic at idle speeds.

If it's a 30/40 mph problem, it may be the T/C locking up. When I had 3.08s mine liked to lock up at 40 mph under light throttle, and it would have a bogging sensation.

Additionally, if the choke isn't working right or is hanging up, it can cause a stumble, not to mention poor fuel economy.

 

[diesel4me]

Also check the vacuum advance and make sure its working...some engines prefer having the advance unit hooked to manifold vacuum rather than ported ,manifold vacuum port will have suction at idle,the ported one wont,only when you open the throttle will it have suction...

The float setting might be off too--too lean might make it feel like its running out of gas at speed,but still idle good...

 

[yeol1]

Mine had a similar problem ended up being old rubber fuel lines ( and a tank selector valve if ya got 2 tanks). I replaced the fuel lined and sending unit and itjust fixed my problem

 

[454Sub]

If your truck runs better with the dizzy hooked to a manifold vac, then your timing is off to begin with. Its to far retarded on initial timing. As that will give you full spark advance from the vacuum pod at idle, and it will retard the curve as you raise RPMs, working against the centrifugal advance.

When did the problem start? Just recently, or after the carb got rebuilt?

 

[fear_nothing]

If your truck runs better with the dizzy hooked to a manifold vac, then your timing is off to begin with. Its to far retarded on initial timing. As that will give you full spark advance from the vacuum pod at idle, and it will retard the curve as you raise RPMs, working against the centrifugal advance.

When did the problem start? Just recently, or after the carb got rebuilt?

Gotcha it immediately starts running rough when I remove the vacuum line from the dizzy. The problem started before I rebuilt the carb.

Don't think its the fuel lines or sending unit as I just replaced the gas tank and sending unit.

 

[Fordum]

Sure sounds like it might be fuel delivery. If it gets worse as you speed up, I'd stick a fuel pump on it.
Don't normally advise throwing parts at a problem, but a new pump is in the $10 to $15 range, and trying to test the old one would take longer than changing it.

BTW you must do a pressure as well as flow test. Had a car that would do great driving around, but would die when you punched it to pass someone.
Usually just as you got alongside..........

Checked the flow rate twice, passed both times. Finally borrowed a pressure gauge, had almost no pressure but would flow fine with no load.

New pump fixed everything.

 

[muddysub]

Swap it for a cummins.

 

[fear_nothing]

Swap it for a cummins.

LOL as twisted as it sounds I've given some thought to that. I HAD a ford excursion with a 6.0 diesel. Worst vehicle I've ever owned. It sure ooked pretty sitting in the repair shop. Can you say more than 10 visits to the shop in 3 years. Unless its Eleanor I'll NEVER own another ford. Lets not start talking about egr valves and rebuilt turbos as I may vomit ford blue everywhere

One day when I'm loaded I might consider a cummins, but that's not today