Re: Poor mileage
Buy a wideband air fuel ratio gauge. I run an innovate mtx-l but aem and others make a good product. They can be bought for around $150 to 200 and either permanently mounted, or just set up on the dash for tuning and removed later.
My 67 Fairlane GT with a 390 4 speed and 4.11 gears used to get 5 to 6 mpg mixed in town and highway driving. The 390 has edelbrock heads and rpm intake, a comp 282 cam and a 750 dp holley.
I found it was idling and cruising at 10.xx:1 mixture, wot got it down into the 9:1 range! No wonder it cranked so good with no choke! Ive leaned it out until it now it idles at 12.9 to 13.4, it jumps around due to the cam, if I lean it anymore the idle gets unstable. Choppy cams will want a richer mix at idle. It cruises between 14.8 or 14.9 at 25 mph, to about 14.1 at 65mph which is about as fast as i run steady due to the rear gear with no overdrive. Wot gets it down into the 12.5 to 12.9 range.
After leaning the carb out my mixed milage has jumped up to the 11 to 12 mpg range, its basically doubled.
I originally bought my wideband setup for tuning gm tbi injection on my rockcrawler, but after using it to set this carb up, I bought another to permanently mount on my Fairlane.
I also reattached the vacuum advance can and adjusted it so it quit surging, which is why it was unplugged years ago. The vacuum advance is helpful for lighting leaner mixtures at cruising speed.
My numbers above are just my examples, youll need to give the engine what it wants while it will still run good, some may get leaner, some not. It depends on your engine, atmosphere, and elevation. Ive seen stock carbed motors cruise just fine at 16 to 1 mixture, you can run leaner with light load without worrying about engine damage quite as much.
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67 Fairlane GT, 390, 4 speed
78 F150 rockcrawler truggy, 351M, 4 speed, 42" tires
Last edited by Tim C; 11-05-2017 at 08:42 PM.