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What would the gas mileage be on a 351W mach I if I adjust the carb so that the secondaries do not open and drive only with the primaries and no secondaries at all? Is it possible to get maybe 14-15 MPG driving only with primaries?
 

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During normal cruising your secondaries are probably not opening much, if at all.. I recently had my carb adjusted so the secondaries would open fully when they are supposed to (they were barely opening before) and have not been getting any worse mileage than before

If you want better gas mileage, will have to jet the carb down and then adjust air/fuel so that it doesn't run lean
 

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Gas mileage has a lot to do with a lot of things. When was your tranny last done, replaced filter on the auto, new oil or so on.What shape are the u-joints in, do you keep the rearend oil topped up, and clean...less dirt less drag more miles..On my 69 I have no problem getting 20 on a Canadian gallon.But I also have everything in near new condition and burn premium gas every so often to help keep the carb cleaned out. I have the timing at 12 degrees adv. Carb settings are 1 3/4 turns out from bottom.Car runs great, lots of get up and go..Another clean out I do is once a year I fill the float bowel on the carb with PowerTune from Mercury outboards. Turn her over a few times and let it sit for an hour.This cleans out all the sludge and the varnish that this new gas??? leaves behind. Driving habits also contribute to what you end results are. rear end gearing also makes a big difference.I also have the 3:00-3:25 gears.
Don
 
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