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Discussion Starter · #1 · (Edited)
Hi everyone. I got this rad 1970 cougar with a 2v 351C a week ago for a hellofa price. Runs really well, except the transition from idle to throttle when car is under load it stumbles. I can leave it in neutral or park and rev it without a problem, but you have to feather the car to get going. Once it gets moving throttle is smooth. Until you let off completely and get back into throttle.

My carb seems to be a 2100 with emissions (has block between intake and carb and EGR with tube going to choke)

The kid that sold it to me said he just couldnt fix the stumble and this is what he did to try to correct it:

1. Rebuilt carb
2. New points, wires, plugs. Adjusted points.
3. New gas tank.
4. Fuel lines, and new filter. ( he thought it was dirty gas)

Here is what "I" have done:

1. looked for vacuume leaks, None found. But engine pulls only about 15-20 psi at idle.
2. Checked timing, distributor has a 2 port vacuum advance, one that retards it and one that advances it. With the retard port hooked up and the advanced unplugged I timed the car at a base of around 12 degrees (which backed off from what he had it set at because I head the car ping under load). With the vacuum hooked back to the advance the distributor does advance when engine is revved.
3. Also rebuilt carb. Found the brass tube (I believe is a booster venturi on one side is cracked) All else looked new as he rebuilt it.
4. Played with many carb settings, mainly the pump lever for the squiters. They squirt great btw.

Cant seem to track it down. Could be the booster, but it stumbles bad enough if you floor it from a stop i dies. I can get photos of everything and videos if need be.

Any ideas is much appreciated.



 

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i get the same thing too with my 289 in my falcon. i've learned to get used to it but when i find out whats causing it i'll post it to help you out.
 

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Discussion Starter · #4 ·
try another carb.. correct app./year , also make sure the egr valve isnt stuck part open . . doest the engine idle smooth?
Yeah it idles fine. The carb is a refurb so I cant find a part number / year on it. Maybe a new refurb carb correct for year and car?

What about a holley 2v replacement?
 

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Could it be a vacuum leak at the throttle blade shaft? Once upon a time a remember having my original carb replaced because it was too worn in the shaft area. I don't remember the exact problem I was having, but we just couldn't get it working properly with all the usual fixes, such as you have done. Does the vacuum fluctuate between 15 and 20? 15 in Hg is low kind of for a stock engine, but 20 in Hg is probably pretty good. I don't know if you can get a bushing kit for that, or if you just have to get a re-man carb, or a new aftermarket one.

RockAuto Parts Catalog
http://www.rockauto.com/catalog/moreinfo.php?pk=1126289
 

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I had a very similar problem a couple years ago with the Cleveland in my falcon. I tried adjusting the carb, I tried adjusting the timing, I tried a new coil and different carbs. It would idle great, it would rev without hesitation or problems in idle but would stumble something fierce every time I hit the go pedal while in gear.

I was pretty frustrated when I figured out what the problem was. When under load, the engine would twist just enough to snag the power wire going to my coil. This old wire was apparently a bit brittle and cracked and whenever the throttle linkage snagged the wire and pulled it forward, it would ground out the wire and steal all the power from the coil. I replaced the wire and re-routed it so that it wouldn't get snagged by the linkage anymore and I've had no problems with it since.

Check your wires, it may have nothing to do with your fuel or vaccuum.
 

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I had a very similar problem a couple years ago with the Cleveland in my falcon. I tried adjusting the carb, I tried adjusting the timing, I tried a new coil and different carbs. It would idle great, it would rev without hesitation or problems in idle but would stumble something fierce every time I hit the go pedal while in gear.

I was pretty frustrated when I figured out what the problem was. When under load, the engine would twist just enough to snag the power wire going to my coil. This old wire was apparently a bit brittle and cracked and whenever the throttle linkage snagged the wire and pulled it forward, it would ground out the wire and steal all the power from the coil. I replaced the wire and re-routed it so that it wouldn't get snagged by the linkage anymore and I've had no problems with it since.

Check your wires, it may have nothing to do with your fuel or vaccuum.
I had the same problem with a 360 in a '76 f250, stumbled something awful, and oddly enough the motor mounts really helped the issue. Not to mention a lot of carb cleaner, head scratching, timing adjustments, and then after all that one day it just stopped doing it.
 

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Discussion Starter · #8 ·
Man thanks for the hep guys...All good things to look for and try. I didnt even think of it being the coil or throttle blades.

The carb is a reman already, but might need a new one...or a holley. Im leaning towards just putting on a edelbrock performer and a 4v holley 600 vacuume secondary.

It could have something to do with the linkage as well?
 

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You could try eliminating the vac advance on your timing, time it with a little more initial timing and let the mech advance do the rest of the work. You can try this and see if it makes a difference.
 

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Discussion Starter · #11 ·
Just wanted to post a quick update...The car is purring like a kitten now
Blew out the lines all the way to the tank, fuel pump was shot, had sediments in it, so I got a new pump and filters. Ditched the rear plastic filter the PO had on it to keep the fuel lines straight and smooth of any turns or kinks. Replaced ann the rubber parts with new rubber line.

Tore the carb down, this time every piece was tore off and soaked in Barryman can of cleaner. I was also able to solder up the crack in the brass tube.

Hesitation is GONE, you can floor is from a stop and go go go! Drives like a new cat.
 

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Discussion Starter · #12 ·
BUMMER! on a fully warm engine the issue returned. Still fighting this problem. Really dont want to break down and buy a NEW carb if I dont have to. As many times as its been rebuilt, same results, this carb is squeaky clean!

maybe its not the carb??? Timing is set at 8 deg, maybe needs more? It sure "feels" like a fuel problem.
 
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