Inliners International Forums General Discussion Ford holley 390 idle speed

Have '81 f250, 300 six w/offy dp, holley 390, efi duals. Timing is set as 12btdc, which is where I want it to be. The idle can't be adjusted below an indicated 950 rpm on my tach, and the idle speed screw is floating free. Other than retarding timing, can anyone tell me if there are internal adjustments/substitutions to the carb that will allow me to get the idle down to 650rpm or so?

Any chance the fast idle for the choke is hanging up or misadjusted? The choke may be fully opened but the linkage is keeping the cam from dropping away? Not too familiar with the 300 Ford but a carb is a carb and an engine is an engine and they don't get much simpler than a Holley.

That was, indeed, part of the problem, and it got me 150rpm. At the choke-side end of the secondary throttle shaft there's a 90-degree tab that bottoms on the carb body when the secondary is closed - I twisted it up a bit and dropped another 150rpm. Finally, comparison with a good shop tune-up tach suggests the cheapie 2" tach in the truck reads 200 high at idle - the indicated 1050 was actually 850.
The 300 now idles at a seemingly accurate 500. Spec calls for 600; I'll try to get the difference back from that tab on the secondary.

Glad to hear you worked it out.

Just curious, does your "cheapy" tach have a way to adjust for the number of engine cylinders? It almost sounds like it is set for a position other than 6. Maybe it is set to 4 or 8? Even a Taiwan special should be closer than a 200 rpm error at idle speeds.

It does, and it is set on 6.
I consider the idle speed problem and its resolution to be fine tuning. Other than this, the holley has been flawless since installation 3000 miles ago, last December. This is a good combo.

Hey, if you replace the duff power brake booster that's leaking major vacume, you not only have better brakes but an engine the idles (barely) at 300 rpm.
What can I say?