Hi, just new here, so hope you can help me over here in New Zealand.
Running a 440 with a Comp Cams Magnum 280 roller solid cam .567" lift I think, and using an Edelbrock Performer manifold with a Holley Street Avenger 770cfm. This is installed in a '67 Coronet 500 with TorqeFlite 727.
Ignition is a 440source non vacuum distributor feed by a Mopar Electronic Ignition box. Timing is set at 18deg initial and 38deg full advance.
Problem is I can't get a quality idle, I have not drilled the idle feed restrictor yet, can anyone suggest a starting drill size?

 

"I have not drilled the idle feed restrictor yet, "

. That' good because you should only drill the throtle plates maybe a 1/32 drill as a start so the engine gets more air so that you can position the throttle blade using the idle screw in the usable part of the transition slot. The idle screw is probable turned in too far which uncovers the slot and affect the transition when you step on the gas. (I'm not explaining it very well) There are lots of Holly tuning books available Also Try setting the timing to 10-12 BTDC, and if the dist advance is adjustable add the rest in the distributor ? If nothing else 18 deg will make it hard to start. What kind of gas are you using ?

 

I should have mentioned I am using our 95octane, which matches the 91 octane in US terms.
I have adjusted the secondary throttle blades to open a little more so that the primary throttle plates sit at the right place on the idle transfer slot. I have been told that this achieves the same result as the drilled holes in the primary throttle plate.
Retarding the ignition makes the idle stalling worse. At 18deg initial, the engine starts fine, but I will try and adjust the rate of advance by stiffening the advance springs if possible.

 

Thumper, welcome to the forum. With that cam,the idle will be a little lopey. Are you using a high stall convertor? How much compression are you running?

 

Thumper -

How did you end up at 18 initial and 36 total??? Seems a little high. As usual, did you check for vacuum leaks and where is your idle speed set? Might be more questions to follow, but that's first.

Archer

 

I would never drill the throttle plates.
That is a band aid for the real fix.
first you need to check your vacuum @ idle in gear
and cut that # in 1/2 for a power valve size
example if the vacuum is 11" then you will need a 5.5 PV
or 7" will need a 3.5 PV
Then remove the carb and with the sec. set screw
turn it in so the transfer slots show an even square
then when you re install it
it will have a higher idle
so then slow it down with the curb idle speed screw
this will take care of a rich Idle
also drilling the IFR (idle feed restrictor) will make it richer not leaner

 

The 440source distributor is mech advance only and thats what is std in that distributor, I know it would be better with more advance in it to give less initial, but a clue is that if it is retarded 5 deg, the idle suffers.
No vacuum leaks and the idle speed is 900rpm in neutral and 700rpm in drive.
The 727 has a stock converter unfortunately.

 

I agree about the Power Valve, I'll try a 4.5" (don't think I can get 5.5").
The secondary throttle plate is adjusted as you said, I know that drilling the idle restrictor is a band aid but I'm running out of ideas here, the idle definately does not improve as it is leaned, gets better richer so thats why I thought the idle restrictors need to be increased.

 

With the right PV and the sec plates adjusted right
you should be able to make it richer with the mixture screws

 

Yes, I think I'll remove the carb, adjust the primary throttle plates until the transfer slot is showing as a square then adjust the secondary throttle plates to spec using the secondary idle screw. I will fit a 4.5" power valve, install the carb and re-adjust the secondary idle until I get the correct idle speed, then tackle the idle mixture screws until I get a decent idle out of it.