396 Poor Off Idle Torque - Chevelle Tech
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post #1 of 128 (permalink) Old Dec 15th, 18, 7:47 PM Thread Starter
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396 Poor Off Idle Torque

From a stop, I’m used to dumping clutch giving gas and driving off. I have to feather clutch as if RPM drops below idle, engine can’t recover & dies.

396/365 engine dyno, tried 670 Street Avenger & 650 DP. M21, 3:73, 20 idle timing, Elgin 1310, 228/238, idle around 850, no headers, small heads, Qjet intake w/adapter

The only way I can drive this thing is to idle close to 950. Sounds like it’s stuck on fast idle.

I’m at wits end
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post #2 of 128 (permalink) Old Dec 15th, 18, 8:10 PM
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Re: 396 Poor Off Idle Torque

20 degrees with vac advance or not?

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post #3 of 128 (permalink) Old Dec 15th, 18, 8:12 PM Thread Starter
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Oh, stock distributor Pertronix conversion, vacuum advance, 93 gas
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post #4 of 128 (permalink) Old Dec 15th, 18, 8:14 PM Thread Starter
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20 w/vacuum plugged, connected when running
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post #5 of 128 (permalink) Old Dec 15th, 18, 8:23 PM
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Re: 396 Poor Off Idle Torque

How does it run once you get going? Good power? You sure you dont have a clutch issue?

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post #6 of 128 (permalink) Old Dec 15th, 18, 8:52 PM Thread Starter
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OK power
Clutch is very smooth
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post #7 of 128 (permalink) Old Dec 15th, 18, 8:56 PM
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What is the issue? It takes a lot of RPM to get the car going? Or the when returning to idle the RPM undershoots and dies?

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post #8 of 128 (permalink) Old Dec 15th, 18, 9:00 PM
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Re: 396 Poor Off Idle Torque

Is this something that just started happening ? Has the car been ok in the past ?

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post #9 of 128 (permalink) Old Dec 15th, 18, 9:21 PM Thread Starter
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Been this way since I bought car last spring.

Issue is very low off idle power,
Have to carefully feather clutch .
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post #10 of 128 (permalink) Old Dec 15th, 18, 9:24 PM Thread Starter
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If engine falls below idle,
it can’t recover,dies
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post #11 of 128 (permalink) Old Dec 15th, 18, 9:37 PM
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Re: 396 Poor Off Idle Torque

check the float level.
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post #12 of 128 (permalink) Old Dec 15th, 18, 9:46 PM Thread Starter
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Moved float from low
to middle no change
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post #13 of 128 (permalink) Old Dec 16th, 18, 12:13 AM
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Add more idle timing, and richen the mixture screws slightly.
What vacuum does it have at idle right now?
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post #14 of 128 (permalink) Old Dec 16th, 18, 2:16 AM
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Re: 396 Poor Off Idle Torque

does it have small closed chamber heads off a 396 402? that cam is not super big plus its on 114 degrees so it should have no problem idling at 750 to 800 rpm. have you checked for vacuum leaks lean idle transfer circuit mixture? try choking the carb by hand with the air cleaner off gradually. note how much if any the engine speed increases
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post #15 of 128 (permalink) Old Dec 16th, 18, 3:24 AM
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Re: 396 Poor Off Idle Torque

Your carb adapter should be divided [ either 2 or 4 hole ] with a dual plane intake. If it is an open spacer, it weakens the carb signal leading to...flat spots/poor transition from idle to the main system.
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