I run #6109 750 dp in line and my clearances are good, and they have secondary metering blocks with side hung bowls..... The difference is the 750s are prob dps and are progressive throttle linkage from primary to secondary barrels while 660s are 1:1 meaning all 4 (8 in a dual setup) open at the same time.... Really it prob doesn't matter cuz if ur running dual carbs on a tunnel ram, the last of ur concerns is mpg
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