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Discussion Starter #1
I have a 72 Chevelle with a 68 327, running points ignition, with an Edlebrock 1406 600 cfm carb and an Air Gap intake manifold. Car idles nicely at 950 rpm in park and 500 rpm in drive. Runs great at WOT and part throttle. Seems like the engine has a miss in it when I just barely press the throttle, maybe 5-10% throttle. Blip it past 10% or hammer on it and there is no issue, no stumble or miss. Plugs look good, all nice light brown/light gray in color. Best lean idle set to max vacuum. Plugs gapped at .035. Tried going one stage rich on the primaries, no change, re-gapped plugs to .045, no change, plugs back to .035 and back to stock jets and rods on the carb. Would have tried to go lean on the carb, ran out of daylight. Manually opened up the choke, no change. Cap, rotor, plugs, and wires are new, running 93 octane pump gas. Before I continue to look at A/F mix, am I missing something? Ran fine with stock, Q-jet and stock manifold.


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Is the Carb. brand new ?
Bob
 

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Put the Qjet back on. :yes:
 

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Discussion Starter #4
Is the Carb. brand new ?

Bob


Brand new carb.


Today 50% of all marriages end in divorce, but 100% of car part deliveries end in happiness.

72 Chevelle Malibu 327/350 Restomod
57 Chevy Bel Air 283/Powerglide
96 Ford Ranger (aka Truck Norris)
 

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Discussion Starter #5
Put the Qjet back on. :yes:


Don't have a spreadbore to squarebore adaptor plate, the Q-Jet stays off.


Today 50% of all marriages end in divorce, but 100% of car part deliveries end in happiness.

72 Chevelle Malibu 327/350 Restomod
57 Chevy Bel Air 283/Powerglide
96 Ford Ranger (aka Truck Norris)
 

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Try bumping up the timing a few degrees and see if it helps. Is it a vacuum advance distributor ? You might have it a little lean too. Is the accelerator pump working correctly at your very light throttle position where you are getting the stumble ?
 

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Try turning the idle mixture screws out 1/4 to 1/2 a turn. You may be having a lean transition from idle to power.
 

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Is the timing the same as it was before?
 

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Discussion Starter #9
Vacuum advance distributor, initial timing is set for 10 degrees, will have to play with it to see if that has any effect, had it at 10 degrees with old carb and intake. Carb is brand new, idle has been changed both rich and lean, no joy.


Today 50% of all marriages end in divorce, but 100% of car part deliveries end in happiness.

72 Chevelle Malibu 327/350 Restomod
57 Chevy Bel Air 283/Powerglide
96 Ford Ranger (aka Truck Norris)
 

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Many E carbs come with incorrect float setting, should be 7/16". Only need to remove airhorn to check it, new gasket NOT reqd if you are careful. The #1406 carb is the 'economy' version & has leaner jetting than the performance version, #1405.
If float level checks ok, you could try the 1405 jetting: 0.100 pri, 0.095 sec jets; 70 by 47 rods.

Also, make sure you see a squirt of fuel when the acc pump is moved.
 

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Discussion Starter #11
Is the timing the same as it was before?


Found the issue, timing was off. I tried changing the rods and jets on the carb and no changes to the carb made any difference to the 'miss'.
I switched from points to a Pertronix Ignitor and reset the timing after the install. I set the timing after the install, and the miss was still there. Checked the timing marks on the balancer and the mark I was using was scribed on the balancer by the PO. Cleaned off the balancer and found the original timing mark and used that mark to set the timing. The other mark had my timing too far advanced. Thanks for the help.


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When i change from points to electronic I keep all the stuff to put it back to points and the tools.
Keep it all in the car in a shoe box or other small box.
You never know when you will be glad to have it.

I have been glad a couple times.
 

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Discussion Starter #13
When i change from points to electronic I keep all the stuff to put it back to points and the tools.

Keep it all in the car in a shoe box or other small box.

You never know when you will be glad to have it.



I have been glad a couple times.


I read the same advice from others and took it to heart, the points are in my trunk with tools to change them. Great advice much appreciated. I installed the lobe sensing Pertronix, seems like others have had better luck with those units.


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