Carb guys, question on driveability issues

[DON SVO]

When under very light throttle, it bucks violently when the motor is cold. Acceleration and decent pedal application don't cause it, only when you're barely cracking the throttle open. Also, it still does it somewhat when it has warmed up but not nearly as bad as when it's cold. Also has a random misfire when idling that goes away when accelerating. Plugs are good, I swapped in another set to rule them out and nothing changed. Cap and rotor appear fine as well.

[Damkid]

I've heard that once the carby's start acting up, they are near impossible to get running 100% again, but carb's are almost like a different language for me so I'll let someone else chime in lol

[WmWatt]

Bucking is an ignition problem, no? Try cleaning the wires, then check timing belt and timing would be my suggestion. Only time my car bucked was after replacing ICM in the distributor and it was gone when shut off and restarted.

[georgeb]

Peak in carb while working throttle (engine off). Should see spray of fuel. If not, accelerator pump circuit inop. Best of luck fixing that!

[Bert]

The Ford truck I've had for 25 years does exactly what you describe now that the choke is no longer optimal. I don't mess with immediate hard acceleration nor fast stop/start until the engine warms up but if you have a clutch you can ride it until the bucking is overcome. Carb engines have to run rich until the engine warms up and that's the role of the damper-like device in front of the carb throat. Carb chokes used to be outright manual (knob and cable coming through the dash) and then went to automatic via a temp-sensitive wound-up bi-metal spring. Wouldn't surprise me if the Festy choke you're dealing with is sensor-electric-control (which currently doesn't work). Should be easy enough to check for. Carb cars will run fine without air filters and VAF and MAF type junk in the way. Get that stuff out of there temporarily so you can see inside the carb when you start and run it. Cold engine should have a closed or mostly closed choke valve. As the engine warms (give it 5 minutes or so) the valve should start opening. Ultimately it should wind up perfectly in-line with the carb barrel.
Festy's are notoriously slow to warm up (takes 1/2 hour at -30 standing still and never does if you're driving at 50mph).
Persevere with all of this man! You can easily grow to love simplicity.

[DON SVO]

The Ford truck I've had for 25 years does exactly what you describe now that the choke is no longer optimal. I don't mess with immediate hard acceleration nor fast stop/start until the engine warms up but if you have a clutch you can ride it until the bucking is overcome. Carb engines have to run rich until the engine warms up and that's the role of the damper-like device in front of the carb throat. Carb chokes used to be outright manual (knob and cable coming through the dash) and then went to automatic via a temp-sensitive wound-up bi-metal spring. Wouldn't surprise me if the Festy choke you're dealing with is sensor-electric-control (which currently doesn't work). Should be easy enough to check for. Carb cars will run fine without air filters and VAF and MAF type junk in the way. Get that stuff out of there temporarily so you can see inside the carb when you start and run it. Cold engine should have a closed or mostly closed choke valve. As the engine warms (give it 5 minutes or so) the valve should start opening. Ultimately it should wind up perfectly in-line with the carb barrel.
Festy's are notoriously slow to warm up (takes 1/2 hour at -30 standing still and never does if you're driving at 50mph).
Persevere with all of this man! You can easily grow to love simplicity.

Simplicity (for me) is a DVOM and pulling codes

[88FestivaLX]

Mine does the same exact thing. I did wires, plugs, cap/rotor and it was the same. It's irritating, but I've kinda gotten used to it, ha.

[Bert]

Simplicity (for me) is a DVOM and pulling codes

I understand what you're saying (sort of): "I can safely turn my brain off and let these electronic devices tell me what to do, and to outsiders I'll appear to be smart because of it".
Now all of a sudden this is your car and you alone are in position to decide what it should do. But there are dirty hands, lots of adjustments and all senses involved. No more 'just look at what the reader says', and promptly bolt on a new part.

Why one day I expect to enthusiastically hear you expound at great length why knowledgeable T Ford owners invariably chose to drive up steep hills in reverse gear.

Sorry Don I'm poking fun at you. Carbs are not as scary as you think. Matter of fact historically many more cars had them than didn't.

[FestYboy]

Don, are you gonna make it to madness? issue can be diag-ed there with Jay (Kartracer) and I on the job.

[DON SVO]

I understand what you're saying (sort of): "I can safely turn my brain off and let these electronic devices tell me what to do, and to outsiders I'll appear to be smart because of it".
Now all of a sudden this is your car and you alone are in position to decide what it should do. But there are dirty hands, lots of adjustments and all senses involved. No more 'just look at what the reader says', and promptly bolt on a new part.

Why one day I expect to enthusiastically hear you expound at great length why knowledgeable T Ford owners invariably chose to drive up steep hills in reverse gear.

Sorry Don I'm poking fun at you. Carbs are not as scary as you think. Matter of fact historically many more cars had them than didn't.

I'm an ASE certified Ford Master Electrical/AC tech. I can diagnose (like actually figure out what's wrong) EEC and OBD systems 'til the cows come home. I don't throw parts, I actually figure out what's wrong. If you're poking fun that's cool, but if you want to talk about code reading part-chuckers that's for Auto Zone and O'Reallys... looking at a scan tool and throwing a new sensor on it that matched the CEL code is the reason I took a 38 year-old tech's job when I was only 21.

Don, are you gonna make it to madness? issue can be diag-ed there with Jay (Kartracer) and I on the job.

No sir, I'm not

[KingFish]

looking at a scan tool and throwing a new sensor on it that matched the CEL code is the reason I took a 38 year-old tech's job when I was only 21.

:laughing6:

[drddan]

Don, is this a stock carb? Or other?

It does sound like an acellerator pump diaphram gone bad....but if it is a stocker carb, it could also be one of those many sensors.

The acellerator pump provides a small squirt of gas into the carb to get the process going till the rest of the carb kicks in.
Bad diaphram= hard stumble

Check around and make sure all connections to the carb are good, and have power to them.

I'll wait till I hear if this is a stock, weber, or...? before I make any judgement calls.

[Bert]

There is an accelerator pump in a Festy carb? drddan is correct in that engines stumble if you press the pedal down and there is no anticipatory squirt of gas down the hole, but I'm still leaning towards a faulty choke (since you say the car stumbles more when it's cold than when it's warm). Carbs are imminently rebuildable. Often there is varnish or deposits interfering with proper operation of jets. Can you blow compressed air all through the thing for a start? Another place to look is at compromised vacuum lines. Small engine guys generally unscrew the jets and clean the orifices and then turn the jets all the way back in until they bottom out. Then one and half turns back out is then a good starting point. Once it idles fine then you start toying with the high speed jet. But could well be Festy carbs are sealed and that you cannot adjust the jets.

[DON SVO]

Don, is this a stock carb? Or other?

It does sound like an acellerator pump diaphram gone bad....but if it is a stocker carb, it could also be one of those many sensors.

The acellerator pump provides a small squirt of gas into the carb to get the process going till the rest of the carb kicks in.
Bad diaphram= hard stumble

Check around and make sure all connections to the carb are good, and have power to them.

I'll wait till I hear if this is a stock, weber, or...? before I make any judgement calls.

It's a literally breand new (reman?) carb. When I bought it the carb had 600 miles on it. I'm talking so fresh that the choke and throttle blade were still shiny.

[georgeb]

Have you checked the choke and accelerator pump function as suggested?