Car has been driven a little over 2000 miles since the engine rebuild June 2019 and its plugs have shown a strange coloring pattern. #1 is darkest, 2 is a bit lighter, 3 lighter still when comparing first three plugs. Last three show quite a bit lighter but have a slight graying of center porcelain. This photo was taken after idling while trying to purge air from heater coolant circuit, which was not successful. (another topic for Monday) Previous plug readings after being driven on highway for 10 to 20 miles have shown the same dark to light gradient only the whole scale is lighter across the board to where the back three have bright white center porcelain, but #1 is still darkest of the six.

Would it wrong to suspect the secondary stop for its throttle plate to be set such the too much idle air is passing leaning out the back three? Holley 390 is a bit long in the tooth.

Note, I have the "Good" intake/exhaust gasket /6Dan recommends. Can't recall the company's name.

During the failed air burp of cooling system, I intended to read the header (Clifford) temperatures of top bend just down line from flange, but did not. In the past those readings show back three to be hotter by 50* or a little more. I'm going to check that Monday.

Additionally after cold start all six cylinders are firing every time, once engine gets to operating temperature 195* and thermostat opens at idle of 800 rpm there is one or more intake valves hanging open to cause that phuff putt, putt, phuff, putt, putt out the exhaust pipe where if a hand is place over end of tail pipe each phuff it is sucked back on to pipe. (yes, true duel exhaust) I asked the re-builder about this valve problem and he said to loosen the lash. At the time I had it set 0.002" over cam card recommendation of I - 0.012" and E 0.012" I have since loosened two more times to: I- 0.016" and E 0.026". Cam is OCG #346, and idles smoothly at current lash setting until it warms up.

I have contemplated flatting up main jet, but front three look to be on the rich side, and o2 sensor agrees when underway 2000 to 2500 rpm. On the interstate at 3000 rpm (60 mph) and above it reads normal to lean mixture, and slight throttle opening drops the A/F ratio gauge off the lean scale, a bit more throttle, and power valve comes on line bringing mixture back to rich normal. All that still does not address the two mixture conditions between front and rear three cylinders.

Could the leaner/hotter condition shown by plug color of the back three be causing an intake valve to be hanging up? Could there be a very slightly bent valve stem that is binding once heated up?

Any ideas to get the phuff gone are welcome. And or if my reasoning is all wet.

_________________
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 take it the carb is mounted with the primaries to the front? Is the intake manifold heated?

Remflex is the gasket.

I would loosen the lash another .004" and see how it behaves hot. If it's still misfiring when warmed up and you suspect a valve hanging up then pull the valve cover to observe the valves. A timing light can be helpful. Do you by any chance have positive valve stem seals?

_________________
Joshua

Yes primaries to front, and hydronic hot spot under carb supplied via heater loop.

Remflex, yes, yes.

Not sure if rebuild used positive valve seals. I checked the bill all it listed was:"12 Teflon valve seals @ $2.25 ea. After checking internet for said device I would guess they are positive valve seals based on price I paid, and a look see of the seal on motor looks to be white with metal ring high on seal.

More investigation takes place this morning, and a funny thing happened on the way to the Forum:

Mileage since last valve lash: 130

Checked lash this morning and they are all over the map; see below.

(1)E- 0.026" / I- 0.017" (2)E- 0.028" / I- 0.016" (3)E- 0.022" / I- 0.016"

(4) I-0.011" / E- 0.028" (5)I - 0.013" / E - 0.024" (6)I - 0.016" / E - 0.025"

To backtrack on what I posted on lash due missing lash setting notes I trusted the dome, It looks like I set intake at 0.016" and exhaust at 0.026". I recall running through the adjustment several times making sure the same drag resistance was felt on feeler gauge for each valve. I did this cold because this engine spits oil all over inner finder, windshield, and fire wall. I also just checked them cold being same temperature they were set; 60 degrees F.

It looks like I have to replace four or more rockers that are have traveling adjustment, [3E; 4I; 5I; & 5E] to which I have four new old stock rockers on hand just acquired a few weeks ago to make the repair.

Today I'll replace the four rockers that moved the most. Is there a shade tree method of stiffening up the adjustment screw action for the few not replaced that need some love?

One more detail is the amount of adjustment screw has left to travel. When I had the engine out, and could get a good look at valve train at eye level, all adjusters looked to be at mid point in their travel.

_________________
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 would not run that cam with less than about 0.018 - 0.020" intake lash. Open it to 0.020" and see how it behaves.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Dart271: Why so loose on intake over a stock cam?

As you saw I have an intake rocker that measured 0.011" tightened up from from 0.016" I would bet that is where the phuff was coming from. After performing the last lash adjustment engine ran at temperature with out any phuffing.

With the lash as loose as it is top end was making quite a racket as if rockers were taking a pounding.

_________________
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 want better fuel distribution turn the carburetor 90°. I ran mine with the primaries to the left, away from the head. I made a bellcrank using a bolt in one of the head lifting holes.

_________________
Joshua

Josh,

I think I tried the 90* turn and seems there was not enough clearance between intake and throttle lever on carb to allow full rotation. Maybe I had the primaries to the right, can't remember. Currently using a 1/2 inch adapter/spacer between Clifford intake and carburetor, and a 2" tall air cleaner; it fills space up and is snug to the hood insulation.

I do have a longer throttle cable on hand, so it is just a matter of re-orientating adapter and plumbing up the fuel line. I'll give it a go tomorrow.

_________________
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

Made a few measurements, Chrysler throttle and kick-down adapter bolted to Holley's throttle lever is about 3/8" too long or in other words will interfere with intake. I'll need to get a thicker adapter plate if they are available.

_________________
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 do not use rocker noise to set lash. I like the tappet noise, myself. I run the car as hot as I think I will run it, and make sure the idle stays stable as it heats up. If the idle decays with heating, I loosen the lash another 0.002" or 0.004" and see how it runs next. Iterate, and back up 0.002-0.004" as needed.

I have run plenty of cams at 0.026 - 0.032" (int, exh, either, both) and not had rocker wear issues except when running hot on a road course for long times.

That cam I set up on the Lemons racecar and my old 64 Valiant and it really liked 0.020"/0.026" lash settings. Too tight will also burn valves more easily. I recently re-set the lash on Seymour's 62 Valiant (medium-big cam) using this procedure and ended up around 0.008" looser than where he had it. I gained 3-5" of Hg idle and was able to smoothly idle it 400 RPM lower and pull away in 2nd gear from a stop pretty easily.

YMMV...

Lou

_________________
Home of Slant6-powered fun machines since 1988

Dart270: Went through quick lash adjustment now intake at 0.020" E at 0.028". Let the engine warm up back three were Phuffs to be detected. Let car idle for 45 minutes, still no phuffing.

I checked vacuum findings below:

600 rpm 10Hg quivering =/- 1 Hg
750 13.5 Hg
800 14 Hg
900 14
1000 14
1200 15
1400 17
1800 18
2000 18
2200 18
2400 18
2600 18
3000 19
3300 19
4000 19

Also made a slight bend in secondary activation rod that pulls the secondary throttle plates open. Now secondary throttle plates stay against their stop at idle. They were able to slightly open and I suspect the additional air has been leaning out the back three cylinders.

Once the old girl cools down I'll pull the plugs for a reading.

Tomorrow I'll adjust idle air screws, take a reading on timing, and go from there.

Engine sounds a bit more robust at idle. Wouldn't loosening lash slightly up compression with this cam?

_________________
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

Yes, you will definitely have a more robust idle by loosening lash (up to a point). It raises idle vacuum, which also indicates you are raising the effective compression ratio at idle and the lower RPM range (maybe up to 2000?).

Lou

_________________
Home of Slant6-powered fun machines since 1988

Lou,

I checked the idle air screw adjustment, they were good where I had set them. Checked static timing: 13BTC. Vacuum numbers are the best this engine has ever produced. My notes indelicate a 6.5 power valve is installed, and 512 main jets.

Started up car this afternoon, it had a bad miss, backed it out side palpated both exhaust pipes indicated something wrong with front three. Went to get a nut driver to pull valve cover and see what I mess up, even though it was running perfectly when parked.

Opened hood, first glance found #2 plug wire was dangling in the breeze; a dumb ass forgot to put it back on after a second plug reading late yesterday. Easy fix. So after a long idle session back three still show no valve hing-ups. I haven't experienced any back spin of engine after shut-down, she needs to be driven to assess that annoying quark.

Car also seems to start easier, and can be driven after a few seconds after start without hot-footing it to keep it running. Next will be the elimination of left foot braking while driving. That's going to be different.

_________________
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