Ok. i'm stumped did a minor choke adjustment to a holley BBS and increased my mileage from 11mph to just over 16mph. Have never see this dramatic improvement without a lot of adjustments and work to the carb.
Here's what I did, removed the carbon from the choke spring and well, confirmed choke was opening and vacuum is good, no linkages hung up, 1/4 increase in cold idle adjustment. remove, clean-inspect jet/needle assembly and blow out bleeder tubes, check for and leakage with none found.
Plug inspection Autolite 65s with a Petronix conversion shows no rich condition, a nice even light grayish-tan and very little oil (over 400k on this motor) to them, they were installed over two years ago and only have about 20k on them.

Over 400k on the slant...must have just seated the rings

My guess is the choke adjustment....IE perhaps your choke was not opening completely before the minor "tuneup".

-S/6

VERY strange that you were getting 11 MPG and your plugs werent blacker than the ace of spades

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

If the choke pulloff spring was gummed up (IE carbon in the choke spring well) it is most likely that the choke spring was opening too slowly. Snce the carbon is gone it now hets up faster, which opens the choke faster, which gives you better gas mileage. It s doing little things like this tha can help get out slant back to the factory mpg ratings instead of the 11-13 mpg most used slants get.

Keep it up!

Reed

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Casually looking for a Clifford hyperpak intake for cheap.

Hey, I drove my Dart home from Ottawa to Hamilton on less than a tank of gas this Christmas. Cost $40 CDN to fill it again with 94 octane premium gas. 6 hours solid driving. Best gas mileage I ever got on a car making that trip. Yep, like Reed says you can do it... once I upgrade to super six intake I expect to see even better mileage.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

Chokes that don't come off all the way take a *serious* chunk out of gas mileage. I am curious whether you have a Holley 1920 or a Carter BBS -- there is no Holley BBS.

My '65 had a 1920 on it at one time that ran terrifically...started on the first try every time, even from dead cold, without the choke. Whoops, that's a problem. Bigger problem was the mileage, 9.8 mpg. I pulled the carb apart, found the "economizer" (power) valve check ball retainer ring had fallen off the end of the metering block. Wow, full-time open power valve. That would certainly explain the easy starting and rotten mileage. I built a Carter BBS for it. It got a slight bit harder to start in the morning (now had to engage the choke) and gas mileage doubled.

If you're trying to squeak out more mileage, next plug change try a set of Autolite 925s. You may have to special order them. They are identical in heat range to your 65s, but have a double-long nose that puts the spark point further towards the center of the combustion chamber. This helps eliminate localized quenchout.

Its a 1920 that was originally used on my 66. Just had to replace the H20 pump also, porosity ate right through the bypass nipple. BTW discovered that a Autozone PN#690 upper radiator hose works for a lower also, just remember to salvage your spring. Will have more information when I head for the Reno area later this month and clock about 2k miles on it.