L78 Rough Idle and Stumbling

[139tech]

Need help with a 69 L78 having rough idle as well as stumbling when I hit the gas. RPM’s fluctuate at idle 200 rpm up and down. Raise the rpm’s still fluctuates but not as much.  Acting like a vacuum leak but I’ve checked all of that including going around with carb cleaner. New cap and rotor, plugs(when I pulled the old ones all of them were wet)fuel filter, Pcv, carbs been adjusted including accelerator pump. Carb is a Holley 4346. Timing set to 18 degrees total 36. Any thoughts as to where to look? Thanks in advance

[william]

Ensure coil is not hooked up backwards. It will run that way, but poorly.

[139tech]

Ensure coil is not hooked up backwards. It will run that way, but poorly.

So the black wire from distributor was going to positive on the coil and the red wire from distributor was going to negative on the coil so I swapped them and now the car won’t start, hmm…

[David K]

Sounds like the float is the issue.

[DuWayne Ladner]

Interesting, also have a 69’ L78 CE engine that was completely redone but the little it run before tear down, same symptoms as 139tech, but would crank and run really well and then would run horrible and just quit. Had the 4346 gone over about 3 times, and same issues each time cranked. Engine man decided to pull 4346 and put new 750 Holley Quick flow and instant problem solved. Oh well 1 deviation from factory correct build of car well worth the cost. Don’t know if this helps, but my comfort still in the positive realm!

[139tech]

So I straightened the wires out and she’s running again albeit the same as before. Atleast my coil wires are correct but I tested my coil which is a Flame Thrower .32 Ohm but I’m only getting .1 ohm. Connected +batt direct to positive on coil but the surging continued. Gonna swap it out for a new one and see how it goes. I’m still leaning towards the carb being the issue. Thanks for the replies thus far.

[NAPA68]

You mention there is a red wire coming from the distributor, as well as a black. That in addition to your comment about a Flame Thrower coil, would suggest there is a Pertronix pick up in the distributor. IMHO, that would be the FIRST thing to get changed out. Others may have different thoughts, but those pick up's have proven to be very troublesome in my experience.

Tim

[139tech]

You mention there is a red wire coming from the distributor, as well as a black. That in addition to your comment about a Flame Thrower coil, would suggest there is a Pertronix pick up in the distributor. IMHO, that would be the FIRST thing to get changed out. Others may have different thoughts, but those pick up's have proven to be very troublesome in my experience.

Tim

You would be correct in your assumption about the pick up. It is an Ignitor 3 pickup inside the distributor. Appreciate the feedback on it as I have 0 experience with this pick up.

[rich69rs]

I would think if the Pertronix module in the distributor has gone bad that the engine would not run at all.

Richard

[139tech]

Problem solved. Previous owner used the factory resistance wire to the coil coupled with reversing the wires positive and negative. Ran a jumper from coil positive to batt positive, car ran great. Resistance wire delete in process. Thanks for all the replies and help with this. Case closed.

[David K]

Glad you found the issue with proper diagnosis and not blaming a perfectly good Pertronix module.