Jeffthunbird

Carb jet not flowing or bad fuel??

ghostrider20

Ohm out your coil. I’ve toasted a few coils, and the symptoms mimic yours.

Kerrmudgeon

I agree that 12* is a little too much for that motor. Set the timing for total advance when you rev it up, say about 36-38 degrees. timing chain stretch and slippage of the damper can change the idle timing mark over time. Also check to see if the mark is bouncing around a lot on the damper. Go for a ride like suggested with the vacuum canister line disconnected and plugged and see if it smooths out under load.
You keep replacing parts that are probably still good. Just costing you $$$.

always keep your old parts to see when you put them back on if the problem goes away. Like the plugs and wires.










.

Frankie the Fink

Still haven't heard if he's checked firing order; we used to call this condition, "....breaking up under load" where a car idles and revs fine sitting still and craps the bed while going down the road. Ohming a coil may not tell the story; typically they start intermittently failing from heat/vibration while the car is moving. One of the few parts that swapping in a new one is the best way to troubleshoot it.

GTOguy

Taylor's are excellent wires, IMO. I would verify firing order, and if OK, would knock the base timing back to about 6 or 8 degrees. It may be getting too much advance. A lot of times, the nylon limiter bushing will wear out and fall off of the centrifugal advance (underside of the weight plate) and you will get too much mechanical advance too soon and it will surge and buck and NOT clear up with RPM.....

tbarb

Just a thought to add to the suggestions here, you don't think tightening a spark plug you cracked a porcelain on a plug.

FWIW, Napa premium wires are made by Belden cable and they are very good.

gowenfast

Have you considered the accelerator pump?

KENS78SILVERANNIV

Update: And I appreciate any... and all suggestions. Eventhough the car is not running well... I'm having a blast trying to decipher exactly what the problem is. Maybe deep down... that's why we all like the hobby. LOL.

O.K. I checked and rechecked the firing order and swapped out the plug wires with another set. Checked plugs and they appear to be fine. New and not cracked. And set timing at 8 deg. No change.

Engine still stumbles and misfires under a load. And watching very carefully now... seems to misfire at idle now....Eventhough it starts immediately with a click of the key.

No fuel smell... but some blue smoke from passenger side exhaust.

Beginning to wonder about the distributor. Has only very slight play in side to side (gear not shaft).

Is there a test for determining if the distributor is shot?? Visual?

I'm going to check all engine grounds today to make sure they're secure.

Suggestions?

vettepoor

65tripleblack

You removed the ballast resistor, so hopefully you used a coil made to be run without external ballast. If not, then the coil is likely dying. Symptoms of a weak coil are exactly as you experience.

And, if your coil is matched, then I'd swap in a new one as a check.

The most likely wires than can cross fire are #5 and #7 on an engine with 1-8-4-3-6-5-7-2 firing order because they are adjacent to each other and the cylinders fire consecutively.

65tripleblack

Ah, you beat me to the punch by a couple minutes.

But your post makes no sense: your emoji says you agree, but you don't agree. FTF has been blaming it on a crossed wire, not the coil. Been watching this thread from the beginning and waiting for somebody to blame the coil. You're the first, even though the rest of your post is cockeyed.

KENS78SILVERANNIV

Thanks for the tip! Coil is new. Swapped back to the old coil just to double check. No change.

Double checked wires. Close to the headers but can't see any cross firing on #5 and #7.

Vehicle has run perfectly for years without the ballast resistor. So I'm eliminating that.

Thanks again.

vettepoor

Frankie the Fink

I hadn't discounted the coil, but I usually vector in on, "....what was messed with last" in these cases.
To wit, new plugs, wires, cap, rotor and fuel pump...

In their zeal to get a little more oomph out of their engine; well meaning owners sometimes screw the pooch....

63 340HP

Confirm the vacuum can has been replaced?
Is the breaker plate ground wire in the distributor still intact, and not pinched or broken?
Is the wire from the Pertronix or points to the negative side of the coil in good condition and not grounding?

Is the timing stable, or does it become erratic above idle, as you read the timing advance on the damper with a timing light and rev the engine up to 3000 rpm, and does it stay stable at a fixed high rpm like ~2500 rpm?

If it is not stable, the coil(s) are a likely problem as others mentioned.

A similar problem can arise from a bad condenser shorting under load and heat. Did you removed the condenser during the switch to the electronic trigger?

A new coil that is designed for use with a ballast resistor will work fine at the higher primary voltage, and then degrade as the winding insulation cooks from the excessive primary voltage. New coils can also be bad, right off the shelf, and the coil location under the tin is a harsh & hot environment that is not coil friendly.

The step down of voltage from a ballast resistor has a fairly minor impact on the secondary voltage and wattage at the spark, when an electronic trigger is used with a matched "performance' coil, as the coil winding ratio is designed to work a larger step-up or increase in the voltage to the plugs. The benefit of a matched ballast resistor and coil is a lower coil primary winding temperature, for a cooler coil temperature, with the same secondary output.

Does the hitching occur without the tin (grounding plug wire ends with tin)?

Have you checked for errant sparking to ground from the plug wires at night with the tin on & off (or, use a dark shop, and ventilation)?

Nowhere Man

you stated the vacuum advance went bad. did you change it out with a correct one?

KENS78SILVERANNIV

Yes as I mentioned above... the vacuum advance unit had a bad diaphragm and was replaced. Slight improvement... but misfire continues.

I don't know what "under the tin" means. Are you talking about the shielding around the distributor? That's been removed.

Intermittent but definitely noticeable misfire continues through power range.

I have tested and installed 3 coils. All test positive for at least 9.5 ohms. One of the coils is brand new.

I will track back wiring in the distributor to look for short or grounding there. It's somewhere.... I just can't find it.

Engine starts immediately with no problem. Will run it in the dark garage tonight with a mirror under the headers.

KENS78SILVERANNIV

Update: 16:30pm Saturday. Put the Taylor 8mm plug wires back on. Car starts immediately. No pumping the pedal ... boom... starts as soon as you click the key. Starts immediately. Runs up and starts stumbling, misfiring as usual.

Checked with water spray on plugs and distributor in the dark... looking for cross-fire or arcing. Found nothing.

Tested around manifold and carb with carb cleaner to see if I could detect any kind of vacuum leak. Nothing. No change in RPMs.

Checked distributor wires... no shorts.

No smell of gas. Jets are delivering fuel. No flooding in carb.

Not sure where to go next. Tried everything I can think of. Suggestions?

Frankie the Fink

If its not electrical then maybe the carb rebuild is faulty....one last thing you can try...
With a tachometer hooked up, and the car at a fast idle, disconnect each plug wire individually one at a time and note the tach reading....the reading should fall by 150-200 RPM. Any cylinder that does NOT cause this drop is your problem...

Re-read 63 340hp recommendations; the breaker electrical wire under the cap can be frayed and work fine sometimes and poorly at other times.

Don't know if its been mentioned but roll under the car and examine the fuel pump at the actuating arm pin and make sure its not "walking" out of position - this has been a problem on some repro pumps for a while.

rtruman