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Old 07-14-2008, 05:24 PM
wixomhead wixomhead is offline
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I have a ford 460 with an 8-71 and dual 750 Barry Grant Mighty Demons with boost ref pwr valves. Cam = Comp Xtreme Energy 262/270 with 110 lobe centers.

Car idles excellent (900RPM) when all 8 idle screws are all set at only 1/2 turn out. Manifold vacuum shows 16+ inches steady at idle. I did NOT connect manifold vacuum hose to boost referenced power valves on base of carbs because .... the engine has STRONG vacuum at base of carbs at idle.

If I back off even ONE idle mix screw only 1/4 turn...the motor begins to surge immediately. The car won't even run if I set the mix screws to 1 turn out or more.

When I DO connect manifold vacuum source to base of carbs (like BG Tech suggests) no difference at all is observed (para #2 still holds true).


Hope I'm adding (not subtracting) to this discussion with above info and the following ?s:

1. Why such strong vacuum at base of carbs? I thought roots type blowers at idle has little/no vacuum, hence the need to connect manifold vacuum at base of carbs to prevent pwr valve from pouring fuel at idle?

2. Does 1/2 turns out all around sound "proper and correct"? Or am I masking something else up.

Plugs look light brown...
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