Sorry for the delay in response, George - can't sit for too long or I get antsy.
Yessir, this is a mechanical secondary 650 Speed Demon; double pumper and all. What I was referring to about linkage was that the opening position of the secondarys is linked to the opening of the primarys. Pretty much all mech secondary carbs work that way and I'm sure you already know that; BUT the "idle" adjustment screw on the passenger side (right side) of the carb is for positioning the secondary butterflys relative to closed and to set proper transfer slot exposure. I suppose it could be used for idle adjustments but I would think it likely to have considerable effect on the idle circuits of the secondarys, i.e. very rich in the part-throttle area and/or possibly lean at wide open, depending on secondary jets used. Primarys do open about 60% before the secondarys start opening, and the squirters take care of that inevitable lean period when air starts to slow down with the opening of the secondarys, making fuel draw difficult.
Whew. How's that for long winded?
The intake is an Edelbrock Performer RPM; ignition is all MSD (Pro-billet distrib, 6AL with rev limiter set at 6200), timing initial 16 degrees, total 36 degrees.
Enlarging the airbleeds just serves to lean out fuel flow at high vacuum periods (idle) but is negated when the butterflys are open and main jet circuits are working (thru the boosters). Depending on where the idle mix screws are set obviously determines how much fuel flows too, but the bleeds basically reduce static pressure in the emulsion tubes and, thereby, fuel flow is reduced. If mix screws are too far in (like mine), then the idle circuit tends to go lean during the transition to main jet circuits and the dreaded stumble results. Too big on the airbleeds, mix screws are backed way out (to get decent idle running)and it usually goes rich in the same transition.
Some fun we have here. To these old eyes, there's damn little difference between Holleys and Demons; supposedly the Demon's milled meter blocks are superior but I think that's crap - I don't ever recall seeing bad meter blocks in any Holley I ever used, and I had my hands in them on Z28's (302's and 350's), big block Chevelles, a couple corvettes, and a LT-1 powered 1975 Vega. They all worked, and pretty well at that. Wanted to try a Demon to see if there would be much difference - but so far they seem pretty much the same. After all, 650 cfm is 650 cfm, is it not?
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