Since I have owned this car, it has had jumpy low rpm vacuum, and on the low side on the road vacuum. When at idle back three (duel exhaust pipes to bumper) have had a skip, where placing or draping hand loosely over end of tail pipe it is alternately blown outward, and rather consistently sucked back to its opening.

I had attributed this to the cam overlap, and by loosening lash was able to reduce idle lope or what I thought was all lope, and lessen vacuum gage flutter.

This condition was still present after a head rebuild with valve job, and as I said I attributed it the cam. A while back I did a leak-down test and valves were holding with no leaks, so I know they are sealing. Now I think there is one or two lifters hanging up, of which I did not remove during head rebuild.

I have a Peanut head, so easy examination or extraction of suspected lifters is not available without head removal. I was wondering if rocker arms & shaft were removed, plugs removed, and engine turned over one could detect a stuck lifter either feeling with a finger on push rod, or using a dial indicator.

Anyone out there in slant world got any ideas for an easy test.

Should I run some bottled lifer un-sticker first to see if it helps? I have been changing oil every 3000 miles or less for the last seven years, and top end looks brand new clean, no sludge, no burnt on carbon.
On the electrical side, over the years I have changed orange box, installed a good grade of copper contact distributor cap & rotor, new distributor pick up gaped ~ 0.008â€￾, and Magnacore wires; so I don’t think electrical gremlins is where the problem lies

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

If you can lash the valves the lifters aren't sticking. Hydraulic lifters will sometimes not bleed down and therefor hang a valve open, but solid lifters are incapable of holding a valve open in this fashion. The only way I have stuck a valve open on a mechanical lifter engine is when the valve rusted in the guide.

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Joshua

So perhaps an exhaust valve is hanging open on occasion?

Would a weak valve spring be a cause?

What are chances its an electrical problem?

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

The exhaust valves are most likely to stick if they get hot and seize in the guides. So under load, not at idle. The shop that did the head work should have tested the valve springs. Did they? Does the power drop off at high RPM?

I think it's more likely a mixture distribution problem than an ignition problem.

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Joshua

My 1960's Chilton trouble shooting section has vacuum reading
for sticking valve as "Pointer drops rapidly but intermittently and
then recovers. Note which valve sticks apply penetrating oil
to one valve guide at a time. Problem will correct itself temporarily."

Sorry for slow come-back, This site is having problems loading on my machine for the last week or so. Keep getting server error messages or site down for maintenance when bring up threads and submitting text.

Josh, Shop did not test springs. I installed valves & springs after measuring their height. I recall several of them were up to 0.060" short or less in length, and about half were all the same length. I had no way to measure their applied force.

Engine has always shown or felt like it has a lack of torque from idle. I have a 2600 rpm stall converter, and has never had much spunk below 3000 rpm.

Vacuum readings with loos lash in 0.024" to 028" produces waging needle 3 to 6 in Hg at in-gear idle of 550 to 700 rpm, 10 to 11 in Hg in park at 1100 rpm, 15 in hg 1600 to 2800 or so rpm, and 17 to 18 in Hg over 4500 rpm. Engine pulls real hard above 4500 rpm, up to 3000 rpm rather lackluster stock build pull, 3000 to 4500 rpm stronger pull. The cam likes rpm.

I can not detect or rather hear that skip, or miss while driving above 1500 rpm. Too much wind & tire noise top up or down, but suspect is still present. I have had folks comment on the blurp, blurp, pop, blurp when off throttle coasting down a hill, or after pass them. I have not been able to hear that back-off sound.

I'm wondering if there is some cam lobe erosion.

About 500 miles or so I pulled the plugs after discovering manifold had un torqued its self, causing a small vacuum leak. 4 of the plugs looked normal light tan #4 was darker and 5 or 6 was lighter. After re-torqueing manifold, driving several hundred miles, plug colors all looked much the same, with #4 now just a shade darker than the rest.

Head has been ported only cleaning up casting warts, gasket matching, and some bowl clean-up with installation of Engine builder over sized valves.

After writing this tome above, I wonder if the Holley 390 has too much idle make-up air passing through the seconday half. I had to adjust secondary throttle plate stop to eliminate a rich idle condition that could not be corrected with primary throttle plate stop opening to keep out of transition slot. Carb is mounted North South orientation.

Maybe I need to lessen secondary idle air contribution, and re open drill holes in primary throttle plates which I made to lean idle out before installation of 02 sensor, and that may richen up the back three cylinders at idle.

Currently I have the lightest secondary opining spring installed, secondary starts come on at WOT around 3200 rpm, and lower rpm when climbing steep hills at part throttle both conditions with a smooth transition with very noticeable stronger pull, and that nice 4v howl.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I think that you would be much happier with a shorter duration camshaft.

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Joshua