My engine will run just fine at cruising speed for a few miles and when I stop, the idle jumps way down to 500 and wants to stall. On initial start up it idles just fine and if I cruise around the neighborhood at 30 to 35 mph, it will still idle fine. Here are the specifics:
396 bored .030
Comp Cams 280 Magnum muscle solid cam
Edelbrock Ram Air manifold
MSD billet distributor and MSD 6al ignition
Holley Street Avenger 770 Vacuum Secondary
70 Primary jets, 75 Secondary jets, 65 Power valve
Timing 14 deg inital 36 total
Yellow spring in the secondary
Floats checked and below the sight glass
Vacuum reads 12 - 14 at idle
Idle at about 900 RPM
I've tried 72 primary jets (too rich) and 68 jets (too lean). It stumbled off idle and at cruise speed increase until I changed up to size 70 and the yellow spring in secondary. I also bumped up the timing from 12 to 14 initial and now the stumble is gone and the throttle is more responsive. If I cruise 5 to 6 miles at highway speeds and then stop, the idle wants to fall to 500 rpm and the engine wants to die. If I keep feathering it to keep it idleing, it finally comes back up to 900 and will idle without dying. I have NOT messed with the idle mixture screws yet. Am I flooding out or starving ? Is my power valve too low?
BTW....this is after a total engine rebuild.
1968 Chevelle SS396
396/375 hp L78
4-speed Muncie M21
3.73 12 Bolt
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