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High idle and air valve difference in carbs 140-160 1971

I'm having an issue with my '71 164 (B30 with 2 stromberg carbs) where the rear carb doesn't seem to be getting the same vacuum as the front. With the car idling the front air valve lifts about 1/4" up and the rear doesnt lift at all. In this state it's idling at around 1400rpm and the timing marks show 10deg BTDC. If you lift the rear carb air valve with your thumb to match the front carb - the idle drops to around 700rpm and the timing mark shows TDC.

I've tried adjusting the idle screws on the carbs to match and this didn't make any difference. What could be causing the vacuum difference or is this even the issue? I'm assuming the air valves of both carbs should lift equally?

I rebuilt the carbs myself and replaced all the gaskets except the bypass valve in the front carb - but I'm not sure this has anything to do with the issue I'm having.

I have a carb synchro in the mail but its not here yet.

You can sort of see/hear what I am talking about here:
http://www.youtube.com/watch?v=Ik3kqQ3fa-g






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New High idle and air valve difference in carbs [140-160][1971]
posted by  164inVA  on Mon Aug 11 06:21 CST 2008 >


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