68 340-S Barracuda-troubleshooting intermittent erratic idle

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fished340

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Need some help troubleshooting an intermittent, erratic idle on an original 340 motor. The problem started just two weeks after the car was running fine. Started her up and the idle issue began. Have replaced plugs, plug wires, cap & rotor, battery, fuel filter, fuel appears good. Checked points, look in good shape (Mallory Duel point distributor). Car has fairly new Carter 600 AVS carb (original equipment). Idle issue happens at idle as well as rebbing in higher RPMs so seems to be electrical. Have not checked coil or condenser and am running out of things to check. When not experiencing idle issue, engine purrs and sounds great. Any suggestions are greatly appreciated!
 
I'm having some similar issues. I'm gonna try sea foam. I'm hearing the gas is really reeking havoc on the old muscle cars. The only other thing you might try is the fuel filter.
 
Do you have an inductive timing light? Try putting the pick up on each wire and see if it is firing, and if it is firing every time and not missing.

Another way to check spark, is to get a spare spark plug and disconnect a spark plug wire from a plug (the front ones work good for this as you have longer wires on them). Then stick the top of the plug into the wire and hold the bottom electrode to a ground or run a jumper wire from a ground to that bottom electrode and look at the spark. Is it orange, purple, or blue? How strong is it?


also pull a spark plug or two (or eight) and see if they are oil/gas/carbon fouled and what color that they are.


Check your timing with your timing light to make sure that it is still ok.

Put a vacuum gauge on it and see how the needle acts. There is a link that tells you how to read the vacuum gauge for troubleshooting, I don't have it handy at this time, maybe someone can post it up....


I would start there....
 
moparker said:
I'm having some similar issues. I'm gonna try sea foam. I'm hearing the gas is really reeking havoc on the old muscle cars. The only other thing you might try is the fuel filter.
Click to expand...


Yep, could be bad gas.... :fart:
 
starting 68 the AVS carb has a lean idle circuit. this can be fixed with a small drill and drill out the idle circuit. i think it is about .033 or .034 " what ever it is ONLY take .001" bigger. take the vinturi cluster out. it has two brass tubes the small one is the idle jet. use a small drill with a pin vise. hold the jet facing down. drill by hand slowly. so the chips fall away from the tube. NOTE: ONLY take .001" out. this is NOT where if a little is good a lot is better.
 
moe7404 said:
starting 68 the AVS carb has a lean idle circuit. this can be fixed with a small drill and drill out the idle circuit. i think it is about .033 or .034 " what ever it is ONLY take .001" bigger. take the vinturi cluster out. it has two brass tubes the small one is the idle jet. use a small drill with a pin vise. hold the jet facing down. drill by hand slowly. so the chips fall away from the tube. NOTE: ONLY take .001" out. this is NOT where if a little is good a lot is better.
Click to expand...


It's not recommended to drill out jets and air bleeds on carbs yourself. Carb manufacturers blend the inlets and outlets for better air flow, drilling interferes with that. It's hard to do it properly at home and you could ruin your carb.
 
Try this....I had this one stump me for a long time.....I would have never thought of it and found it by accident!... Pull the distributer....the gear that drives the distributer and the oil pump and is geared to the cam...give it a shake with a screw driver in the slot...my problem was the bushing in the block that holds this distrbuter gear was worn and caused the irratic idle. The gear was sloppy and caused the timing to bounce around. It may not be you issue but its an easy check :) . I am so curious if its the same trouble I had?
Good luck, hope this helps!
 
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