JetForceF22

Hello, I have a 1972 K-20 4x4 with a 350 small block with a 650 cfm Edelbrock 4bbl carb. It runs great and idles fine, but if I punch it, the engine sputters, then "comes to life." I would like to eliminate the sputter, I am thinking that when I mash the pedal the secondaries are temporarily flooding the carburetor? And if this so be the case how would I go about tuning it to fix this? I am fairly new to carburetors so any help would be greatly appreciated.

(More details about my truck in my signature.)

bowtieguy79

iTrader: (1)

Have you ran the throttle by hand with the engine off looking down in the carb at the secondaries? Its possible that they are gummed up from not normally being open. If this is a new problem that came up, I would look it over well, if you see that they kinda flip open under pressure, I would use a can of carb/choke cleaner while running the engine and blipping the throttle.

There are a ton of other questions too. How old is the carb? How old is the coil, plugs, wires, cap rotor... But I'm sure you covered those.

Tootall

iTrader: (79)

you might have to re-jet the carb . . .

look down it with the engine off, open the blade and watch how the fuel gets dumped in. It could be a combination . . . jets - too big/small or gummed up. Do you know the size of the float valves?

any backfires when you get on it or at the top end ?

JetForceF22

Thank you for your replies, I'm not sure how old the carb is, I but the truck in WV last year, it was a little dirty other wise in good shape. The carb has done this for quite awhile, I just now have the time to address it.

Toot- I do not know the size of the float valves, the carb backfires once in awhile but its rare. Last backfire was last month if I recall, so its been awhile.

I'll check and see if its gummed up, I have some carb/choke cleaner on hand so I can give that a shot. A older guy at AAP said I may not be getting enough air into the carb, and he told me to re-tune the idle air/fuel mixture screws and see if I have any luck with that.

KySilverado

iTrader: (7)

If they are vacuum secondaries the secondary butterflies could be opening to slow or fast, a big bog usually is to fast, sputtering to slow.

JetForceF22

Hmm yes good information- well it sputters for a second then "comes to life", how would I go about tuning the vacuum secondaries?

cttandy

iTrader: (12)

I just sold an old jeep with a carter competition 750 cfm carb on it. Edelbrock bought carter out, so it's the same basic carb. Everything is mechanical, nothing vacuum controlled. Mine was doing the same thing. I got a vacuum gauge and dailed the carb.

It ran a million times better across the board. 5000 lbs on 33x12.50's, smoking them from a punch anything below 20 mph. I guess that tells me it worked, cause it wouldn't do anything before hand.

I had people keep telling me the engine had to much carb on it and it would need to be rejetted.

Do what I did. Ask around, find you an old timer that know carb's well. Ask questions, then ask if they would be willing to help you out and show you a few things.

JetForceF22

Yes I already ran a vacuum gauge at my buddies house and the carb is holding 18 steady which is fantastic, but that doesn't help the off idle problem of sputtering when I floor it. I just tried re-adjusting the idle air screws and sprayed carb cleaner down the whole carb, no luck.

truckmann

iTrader: (8)

Here is some info that may be useful to you. http://www.mustangandfords.com/techa...ing/index.html

Ya I know it a mustang and ford forum but the info looks good. Sounds to me like you are getting too much initial fuel when you go WOT. Been too long for me to remember my days with the old edelbrock carbs to be much help with what to work on though.

JetForceF22

"The little tube is the secondary accelerator shot nozzle, which helps prevent stumble when the secondaries open. It allows raw fuel to spray into the secondary throttle bores when the accelerator is mashed. [...] The accelerator pump sprays liquid fuel into the throttle bore as the throttle is opened to help prevent hesitation. The amount of fuel sprayed into the bores depends on the pump discharge nozzle size, and how aggressive the pump shot stroke is. The pump shot is changed by adjusting the location of the pump rod. When the stroke is lengthened, we increase the amount of fuel sprayed into the bores by the accelerator pump. Decrease the stroke and you will have less fuel." (http://www.mustangandfords.com/techa...ering_jet.html)

This might be the reason that my throttle stumbles when I mash the pedal, I'm either putting too much fuel or not getting enough, its something I'll see if I can look into. Thank you Truckmann!