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Old 06-13-2009, 04:32 PM   #1
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Just took two serious steps

I dropped in my new metering rods today, should run ~10% leaner if the graph in the carb book is to be believed, and also re-set my lean best idle. So far so good!

I just dropped my speed from obeying all of the 50 and 55mph speed limits on my commute to doing 40 and 45, plus redoubling my efforts on keeping the acceleration slow but steady, and taking advantage of any coasting. This alone netted me over a 10% improvement in my last tank, and I am hoping for another 10% from the metering rods. That would mean 17mpg!
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Old 06-13-2009, 05:25 PM   #2
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10% leaner doesn't necessarily mean 10% less fuel, since you'll probably have to use a bit more throttle.

But I'm very curious about your results - I've been getting around 17 MPG lately on my big block, and I'd love to know if leaning does actually help.

-Bob C.
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Old 06-13-2009, 05:41 PM   #3
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True, actually I hadn't noticed the 10% leaner and 10% improvement in FE being the same...the latter is a number I've purely pulled out of thin air, I can assure you I didn't base one on the other. The numbers will tell the full tale. Who knows, maybe the pumping losses will be less as well. But my commute has a lot of cruise in it, and not a huge amount of acceleration, so I think it will make a meaningful difference to lean out. At the least, I'll quit getting so much sooty buildup on my tailpipes and I won't have to deal with carbon buildup so much. That alone would be worth it, but I know that there's more FE in my car given its weight and displacement vs. the numbers I actually get out of it; it's poor even by the standards of Mustang enthusiasts who hardly drive for FE.

BTW that's a strong showing out of a 455. I'm always impressed by numbers like that though I've seen them before...
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Old 06-13-2009, 05:46 PM   #4
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Thanks. I've heard of 22 MPG out of a 455, although in my mind it was very poorly documented (basically akin to rumor).

By the way, if you are leaning out a mixture that is too rich, which is very possible, then not only will you be running 10% leaner but you might also use *less* throttle. (I was assuming you were starting from a perfect 14.7:1 but this might not be the case, especially if you have sooty tailpipes). Then you'll be cooking!

-BC
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Old 06-13-2009, 05:55 PM   #5
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Oh yeah, at cruise it's way rich. I get a huge amount of soot and I recently had to blow some carbon off a sticky valve, and like I said the FE was way off where it is for most others' well-tuned Mustangs of this vintage...15+ is the norm where I struggle to make 14 on my commute. I also think it was a bit rich because after I dropped in the metering rods but before I even re-curved the idle on the carb, it idled smoother both in gear and in Neutral/Park. My power setting is dead on, when I had it dynoed I was right at stoich, but if you understand Edelbrock/Carter carbs, the metering rods have both a cruise and a power mode, so if one's spot on the other can be way off. The only thing that bothered me is that the plugs didn't really show it running rich but for one fleck of carbon on one of the plugs after it'd been in storage for two years...
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Old 06-16-2009, 06:39 PM   #6
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Don't forget to run the idle mixture as lean as possible as well. At smaller throttle openings(45 m.p.h. cruise)the fuel supplied by the idle circuit makes up a large percentage to the total used.
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Old 06-17-2009, 08:20 AM   #7
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Yup, got that idle setting taken care of. Might re-set it though, I'm not 100% satisfied with it.
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Old 06-17-2009, 07:19 PM   #8
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Well, I went a bit too aggressive with my metering rods...the ,070" units left me with a noticible stumble transitioning off of the idle circuit, and at cruise it bucked and surged - barely, but noticibly. I backed off to ,068" units and all seems well today, it drives just as it should. It's in the 90's here and I have noticed no pinging, no stubling or surging, and no noticible increase in engine temp. I think I need to re-do my idle setting though, it doesn't feel quite right. And I'll look at the accelerator pump as well.

The results speak for themselves, IMHO...I got to the halfway point of my gas gauge at 166 miles...that used to only take 120miles. We'll see how it sifts out at the next fillup!
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Old 07-18-2009, 11:09 PM   #9
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Holy **** it worked! Every tank (5 so far) since I got my metering rods changed has been over 17mpg. That included some 70mph time, and some aggressive driving, which is impressive considering 17mpg was unobtanium before. One tank was even a PB at 18,36mpg! I am happy!
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