On my "new" '72 dart the 68K motor runs strong and quiet. Gets good mileage and such and always starts right away..

BUT

It has a miss at idle. I pull #1 and #6 wires and nothing changes in the idle. The car just had a full tune up.

This just the way of the beast?

I ran the valves..all good there.

I never had a /6 that ran this quiet so ive never noticed how they idle.

The hopped up slant that i had in the scamp is FAR some stock and it had solid mounts so i cant really compare with that.

Mine is running rough lately... but I think it's due to leaky manifolds. I can't enrich my mixture and it's running hot. Smooth as glass while the choke's on though.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Hmmm, no, mine hits on all six at idle. Maybe jetting it up some will help?

Since the problem is localized to two specific cylinders, jetting it up will not solve the problem but will spoil gas mileage and cause increased engine wear due to oil washdown.

If your power balance test shows no change at idle on 1 and 6, compared to the idle changes you get when you remove the plug wires from 2, 3, 4 and 5, then there is a problem in 1 and 6. Could be mechanical (poor valve sealing due to burnt valve, bad ring(s), etc.), could be electrical (bad/no ignition in those cylinders), and could be fuel(improper carburetion) or air (vacuum leak) but it will be very much worth your while to find and fix the problem.

This is NOT "the nature of the beast". A Slant-6 that runs correctly hits on all six, all the time, and has a smooth idle. I've had rough idles that behaved just like ignition troubles persist through a complete ignition overhaul AND several carb rebuilds, only to disappear with the installation of a different carburetor.

What do the 1 and 6 spark plugs look like compared to th eothers?

When stock my truck always missed on #6 at idle...no matter what I tried (I have no idea why #1 did fire). I went through two NEW, not rebuilt, holley 1 bbls, new plug wires, plugs, cap&rotor, changed jet sizes (well, had them changed, I knew squat about carbs at the time)....The misfire finally disappeared the day I put my MSD ignition on (it had a supersix, headers, and a cam by then though...) Never an idle misfire since. $0.02

-S/6

Probably a vacuum leak in the #6 intake tract, then, on your truck.

An unlit propane torch never revealed such a vacuum leak. Personally I think it was the lean-burn ignition. The spark it provided wasn't great, all 6 plugs had spark, but not a bright blue spark, more yellowish/white.

The MSD also increased my gas mileage, which is likely a sign the stock lean-burn ignition was pretty weak, or was on its last legs.

Assuming you have standard electronic ignition, you may want to check & compare the 'quality' of spark each cylinder is receiving. At the very least this could eliminate a weak ignition as the problem.

-S/6

You're probably right about the weak spark. That said, I have had vacuum leaks that an unlit propane torch (or any of the other popular tricks -- carb cleaner spray, etc. ) would NOT reveal, especially when the leak is on the bottom of the runner-to-head junction, and I've had 'em in very strange places (in the manifold casting itself, at the vacuum tree, etc.)

Ive checked for vacuum leaks...the plugs look normal. Like i said the car runs smoooooooooth under a load or when its moving. Just at idle. The car has power 9" drums so tomorrow when its not raining im gona check there for a leak.

check for a hung valve. maybe the valves are tightened down and they do not close to allow for the combustion. I know when i rebuilt my slant the first time I went half way thru break in with my 3 and 4 holes with hung valves.

Are you sure your #1 and #6 wires arent crossed?

Pyper, great suggestion on the hung valve -- it only takes an adjustment just a little too tight to dramatically worsen engine idling. The trick here is to slack off the tappet adjustments for 1 and 6, especially the exhausts, and see if the idle improves. If so, go ahead and readjust all 12 tappets properly.

By the way, CRalt, is this the 68k green '72 Dart that I saw on Ebay some months ago? Don't remember which state it was in, but I remember thinking "Man, what a great car!".

My truck had a miss at idle. It was caused by a combination of things.
my alternator had low output at idle,poor ground connection and holley factory rebuilt 1945 with worn throttle bushinings. I replaced the alternator,increased idle rpm and cleaned up the ground connections on the motor. This seemed to solve my problem. Good luck.

I relooked at the plugs and couldnt see anything wrong....other then they where champians. So I got some autolite 63's and put those in. Helped a bit.

I dont know if this car was on Ebay. I got it from a guy in connectiuct.

http://members.aol.com/cralt/dart1.jpg
http://members.aol.com/cralt/dart2.jpg
http://members.aol.com/cralt/dart3.jpg
http://members.aol.com/cralt/dart4.jpg
http://members.aol.com/cralt/dart5.jpg

oh. my. god.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Huh?