can you get it to idle any better by adjusting the idle mix after it is warmed up?

Have not checked fuel pressure. Pump is a Carter mechanical street pump. It will pull hard to 7K so I doubt fuel pressure is a problem but I can still check it.

Fuel line is clear of hot stuff and I run a spacer under the carb. I have avoided going to an electric pump but this maybe the year I change it.

New fuel filter

I gutted the choke housing, no choke mechanism.

3 year old MSD Blaster, mounted on the intake. I asked here before if it could be getting too hot but the consensus was no.

New dist. cap and rotor, reluctor gap set correctly

11" of vacuum by a gauge at idle

I do have an old AFB I could throw on there

I can try an new ballast resistor

Coil wires are tight and correct

Engine grounds are factory located and tight

I've tried it @ 2 and 2.5 turns out and no change to speak of.

Interesting, I'll bet standoffs would be and option too to get some airflow around the backside.

I have run many years with a mechanical fuel pump in extreme heat with no issues...

An electric pump is not necessary...


Can you say with certainty that you are not experiencing percolation???

What type of fuel do you run???


Pump 'fuel' ain't gonna get it...

Especially where you live...

It very well could be vapor locking at higher temps especially in the summer. We have crap for gas 91 alcohol infused octane is as good as it gets. I know guys will say to put it under pressure to keep the boiling point higher which is why I have entertained going electric in the past.

In a word-race fuel...


You've got to address temperature if yer gonna stay mechanical...

Together with proper supply and return...


I've been running a 'mix' going way back...

Make one change at a time. Replace battery and go from there.

Definitely battery first. The voltage regulator hasn't been replaced since I've owned the car (17 yrs), but it was replaced during the restoration so its not 40 years old either.

I would suggest plumbing in a gas can with several gallons of race gas or other appropriate fuel to the mech pump inlet & see if that cures it. that would confirm or elim percolation.

Interesting to see what the issue will be.
I ran a 160 degree thermostat in my 451 engine. Sounds more like a fuel level/vapor problem.
I can say that I have had problems with the Mopar Electronic ignitions, but not as you are describing. I have CD ignition systems (MSD, Crane) on my cars. The multi-spark at low RPM helps clean up the idle.

Can a bad battery cause a rough idle? NO, as long as the alternator is working.

As soon as the engine starts running the bulk of the loads are handled by the alternator. It's only when the alternator can't make the required amperage that the battery is called upon.

Get a digital voltmeter and measure across the battery terminals before starting (~12.7V) and then start the engine measure again. It should be between 13.5 AND 14.5 VDC.
Now switch the voltmeter to read AC voltage. Check across the terminals again. The voltage you may measure is called ripple and if it's more than, say, 0.2VAC you have a diode either going out or dead.

If turning the idle mixture screws from 1.5 turns to 2.5 turns out from lightly seated does not have an effect on the idle quality, then the engine is not running on the idle circuit or you have an air leak that is causing the power circuit to open, something like that. You could probably read a writeup or two about setting lean best idle.

Good Luck!

R.

WHat is your fuel tank situation? Ever been cleaned? I was dumb enough to rebuild my carb without checking tank and guess what. It got clogged again. Go figure!

The tank was new when I bought the car. I have put less than 5,000 on it since 1999.

I have the same ignition as you. I can remove the battery and it will keep running fine. I would think that it would need to be both the battery and alternator issue to drop the voltage low enough for the problem.

Add one more thing to look for - engine off - remove the metering rods caps (don't drop the screws in the engine) - start it up and see if the metering rods are bouncing up and down or are they sucked down and stay there or are they up and stay there. If they are bouncing around - hold them down and see if the idle smoothed out. If they stay up - push them down gently until they seat and see if the idle smoothed out while warm. Your comment about surging after warmed up - sounds like they rods are bouncing up and down. The other thing to do is watch the timing when this surging is happening - if vacuum advance equipped - could be contributing to this - and if you have one light and one missing centrifugal advance spring that could as well.

After playing around with springs I ended up going back to the silver springs out of the strip kit. They were staying put when I checked them. The idle is OK in Park or N after it gets warm but in Drive is when it wants to idle down and surge and act like its missing. The vacuum advance is not hooked up. Both springs are connected in the dist.

sure sounds lean. Keep after it, we'll work till we fix it.

i had something very similar happen to me
if there is enough juice in the batt to start it up
that is your highest demand out of it so it is most likely ok.
heat and cold will effect the diodes when they are weak
try changing out the alt with a known good one

Did you check the rods when warm in gear or just in neutral and park. If this unit drives down the road when warm and doesn't miss under load how can the spark be suspect - under load down the road you place more demand on the ignition. Something is not adding up.