An engine build refresher:

225 cid; .030â€￾ over

Head shaved .076â€￾ compression 9.5:1, oversized valves I=1.44â€￾ E= 1.70â€￾
cam Intake duration 235* lift at valve 481â€￾ @ 99*--- Exhaust duration 236* lift .486â€￾ at 113*.

Holley 8007 or in other words 390 4V vacuum secondary jetted at 57
Clifford headers & intake Duel exhaust.

Re-curved electronic ignition, to keep base timing before advancing at 1600 rpm, all in at 2700 rpm.

Orange box, blaster 2 coil, base timing set to 12* BTDC
Transmission 904, 2200 rpm stall converter on a good day…

Suregrip 3.55: 1 gears, turns 3000 rpm at 60 mph

Caution this is a long saga.

Now on with the problem at hand:

For the last several years the engine would idle in gear @ 700 rpm, pull a wagging 2â€￾ to 7â€￾ Hg of vacuum, and in park at 1000 rpm pull 11-12â€￾ Hg of vacuum. Lash setting has been .025 Intake, and .026 Exhaust. Engine would more often than not spin back at shut down.

I installed an o2 sensor last fall to aid tuning the carburetor. After fiddling around with various jet, power valve & secondary spring combinations I settled on 54 jets, and 2.5 power valve. Primary throttle plates were drilled.

The carb ran into the mid rich zone at cruise, drops lean under light throttle comes back to rich under WOT.

I got it into my head the perhaps the carb was not set up properly after reading some new information posted on Holley’s site. Removed carburetor, adjusted secondary throttle plate stop so about .025â€￾ of transition slot is showing per web site, soldered up the drill holes in primary throttle plates, reinstalled carb, adjusted idle screws by vacuum gage. This new set-up provided bit better vacuum at idle in gear, and then went for a test drive.

After a mile, I stopped for gas, the engine would not drop below 1800 rpm, and did not respond to idle speed adjustment screw, but did shut right down with no spin back… something not expected. Went back home found timing had jumped to 20* or more.

I reset the timing, to 16*, fiddled with idle mixture, and idle speed adjustment, and got it to idle rather smoothly in gear at 850 rpm showing over 5â€￾ Hg of vacuum, and in park idle at 1100 rpm with 12â€￾ Hg of vacuum. This was a big improvement over previous readings.

Today I adjusted valve lash to 0.016â€￾ intake, and 0.020â€￾ exhaust, reset idle mixture with vacuum gage, adjusted timing & idle to 900 rpm in gear, and 1100 in park, went for a test drive. Vacuum readings were a few inches higher than past settings, idle vacuum in gear stabilized at 6-7 inches with fairly steady gage and in park 13â€￾. Mixture seemed to be less lean under light acceleration, and engine sounded more aggressive. My redneck dyno confirmed the engine had more low rpm spunk with an easy burn out, this is something new. Previously it had been a turd.

After more tuning attempting to squeeze out a little more steady vacuum at in gear idle, the timing jumped once again into the mid 20* range yielding 1900 rpm.

While trying to figure if carburetor was causing an increase in rpm, to the point of getting into the mechanical advance which is rapid once past the 1600 rpm point, or the timing jumped, I discovered if by hand the secondary throttle plates were seated more firmly on their stop Idle would slow, and if turned slightly the other direction idle would jump 4 or 500 rpm.

I’m beginning to believe that the secondary throttle plates maybe the culprit where they won’t stay seated at idle.

What do you think, and is there a way to stop the flopping of the secondary throttle plates?

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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 would be worried about those timing jumps, if I am understanding you.

Sounds like a junk carb given all the shennanigans. Is that the only carb you've ever tried on that engine? My two experiences with old 390s were terrible. How much is your time worth?

Lou

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Home of Slant6-powered fun machines since 1988

Lou,

Writing that long drawn out play by play, explanation helped me think about what is going on with this thing. Each time I have had the timing appear to advance has been after a bout of boy racer winding the piss out of it, which activates the secondary’s than with the secondary throttle plate cracked open a bit too far the idle won’t drop below the magic 1600 rpm allowing the light mechanical advance spring to pull in the weights.

I need to see a photo of virgin Holley 390’s secondary linkage to identify if it is loose, or presses the back side of the long slot in the secondary throttle lever. I suspect that the linkage holds the throttle plate to its stop screw; mine doesn’t.

After reading, and talking with Holley Tech about their revised tutorials, I believe previous tuning problems were due to a misunderstanding on my part as just how the secondary idle circuit has to be set up.

Below is a photo of said slot at end of pencil. There is a small space between the linkage rod, and end of slot. This space allows the secondary throttle plate to crack open uncontrolled.

[img]http://i294.photobucket.com/albums/mm87/wjajr/Dart%20Engine/001.jpg[/img]

This rod looks to have been bent in a previous life, and needs to be readjusted to just kiss the right end of that crescent shaped slot to prevent any uncontrolled movement of the throttle shaft.

As the primary throttle shaft rotates open to WOT, that “Lâ€￾ shaped rod slides down to the left allowing the secondary throttle shaft to rotate open by a vacuum operated diaphragm located on the other side of the carburetor.

I haven’t messed with the car today, just waiting for a few additional ideas from folks that have the same set up to pipe up, and a warm dry day to blow into the neighborhood.

Bill

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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

Your idle vacuum readings look way too low for a cam with those numbers and an engine operating at sea level. Double-check with another vacuum gauge, but I think you've got a fairly large issue in here somewhere, and I do suspect your carburetor. A 300rpm difference between Park and Drive idle speeds, needing to set a Park idle speed of 1000 rpm to get a Drive idle speed of 700 rpm, is definitely not right. Neither are those lousy vacuum readings.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

You are correct in that aspect... needle nose pliers and holley's are made for each other it seems... Ppl do some strange things to them for tuning for their particular set-ups. straighten the rod as you suspected and your erratic idle problems should go away.

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MRO....

Cheap, Fast, Reliable.... Pick 2...

Doc:
[quote]I am assuming that the 235* is duration checked at .050 lift. ( the .481 valve lift number is my "tip-off")
If so... that is a lot of cam for the street.[/quote]

Yup measured at .050â€￾ lift.
Duration at .006â€￾ lift: I = 315degrees; and E = 314 degrees. Lots of overlap. This car is a former drag queen... LOL


Mr. Stale Flatulence:
It’s the first time we have met, so I'm a bit more formal this time around… LOL

[quote] You are correct in that aspect... needle nose pliers and holley's are made for each other it seems... Ppl do some strange things to them for tuning for their particular set-ups. straighten the rod as you suspected and your erratic idle problems should go away.[/quote]

I shall give her a little tweak, and then a thrashing in the AM.


Dan:
[quote]Drive idle speed of 700 rpm, is definitely not right. Neither are those lousy vacuum readings.[/quote]


I may have miss typed: park idle = 1000 rpm; in gear = 800 rpm with a good lop. I can get it down to 600 rpm perhaps lower, but engine does not like it, very pronounced lope, making valve adjustments difficult on the dance floor.

Once I correctly adjusted secondary idle circuit, the in gear idle moved up to 900 rpm or so, and in gear idle about 1100 rpm. No hard consistent figures with new carb settings as I was still dialing it in. However at 900 rpm, vacuum is up to a fairly steady 6-7â€￾ Hg, and a lot of that lop is gone. Engine sounds real healthy with a nice growl.

At 7â€￾ Hg idle, I can move up to a higher set point power valve which should improve light throttle response & mixture below 2500 rpm.

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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 believe that link is a "mechanical closer / override"- ie. it's supposed to force the secondaries shut IF they stick wide open. The general design looks to be way too sloppy to positively close the blades down to idle position. AFAIK your vac pod (& spring) should hold the secondaries against the idle stop. If it sticks open some then you could have a tweaked shaft, worn shaft bore, sticky link at the pod, possibly a pod diaphram that's "pinched" wrong.

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63 Valiant Wagon
225 - 4 bbl

Preliminary testing after adjusting secondary linkage indicated that was a cause of several years of carburetor frustration. Idle did not run away running up mechanical advance, a good sign.

Holding the secondary throttle plates at their stop produced an additional five inches of much steadier vacuum at idle over previous tunes after a quick idle mixture & timing adjustment.

Out on the road, mixture looks to be less lean at light acceleration, right on target under heavy acceleration. At WOT previously vacuum gage would dropped to zero, now stops at 3 inches. I didn’t drive long enough to get a read on when the secondary’s open, but there were no flat spots indicating the tune is getting close to ideal.

Now with a about 7 inches of vacuum to work with at an in gear idle of a little over 800 rpm I shall change power valve to open at a higher vacuum level.

Tomorrow I will play around with this some more. Today my father is celebrating his 90 birthday, the house will be soon be full of family, and I’m cooking. Oh we are in for a week of sun & temperatures above 50 degrees highly irregular for this neck of the woods in March.

Bill

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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