Poor mileage - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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Old 11-01-2017, 04:21 PM Thread Starter
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Poor mileage

Only getting 8.6 mpg. Car runs smooth, cruise vacuum is 18, rear end 3.0, stock cam. I can't see the pointer very well but the timing is advanced to just short of where its hard to start. The Diz has Accel pointless but I know nothing else about it. The coil has gotten pretty hot in the past, maybe it's not volting enough.
I have lots of questions and only one, ugly, truth -- 8.6 mpg. Wonder where is a good place to start improving.

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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Old 11-01-2017, 07:17 PM
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Re: Poor mileage

Sorry Puttster for your problems. Have you checked the carbuerator? float may be sticking. what size motor are you running?
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Old 11-01-2017, 07:44 PM
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Re: Poor mileage

Quote:
Originally Posted by puttster View Post
I can't see the pointer very well but the timing is advanced to just short of where its hard to start.
How is your vacuum advance connected? It should be connected to a point below the throttle plates to receive 100% intake manifold vacuum. Manifold vacuum is high at low engine load, and lowest at high load. Say you have initial advance set to 8 degrees and your vacuum canister adds 16 degrees. Therefore timing will be:
• At starting 8 degrees initial + 0 vacuum + 0 centrifugal = 8 degrees total (easy to start)
• At idle 8 degrees initial + 16 vacuum = 24 total (should idle smooth)
• at 3400 RPM cruise 8 initial + 18 centrifugal + 16 vacuum = 42 total (good economy)
• If you push the throttle at 3400 RPM the total advance will be about 8+6+18= 32, which should prevent pinging.
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Old 11-02-2017, 01:27 PM
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Re: Poor mileage

What would you like to get for mpg? If the engine is tired and I seem to recall that you have the old, original type A/C compressor then an old 390 4V with A/C might be doing pretty good at 8 - 9 mpg in the city. There may not be much room for improvement, especially without spending $5K+. Our gas jumped 12 cents/ litre last night and we're up over 20 cents / litre in the last couple of weeks (WTF), but you can buy a lot of gas for the price of a new engine and EFI conversion.

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Old 11-03-2017, 01:15 PM
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Re: Poor mileage

I get 8-9 mpg with mixed city/highway driving. I have a 390/4V 3 on the tree.

The engine has ~8k since rebuild and the carb was rebuilt about a month ago.

Correct me if I'm wrong, but I don't think you're too far off the mark at that mileage!
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Old 11-03-2017, 07:14 PM Thread Starter
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Yikes. Seems like folks here report 15+, i wanted something like that. What was the mpg in 1965, i wonder? And if it was 15, what caused the difference over the years?

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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Old 11-03-2017, 09:45 PM
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Re: Poor mileage

In '66 I had a '65 Galaxie convertible, 390 4 bbl, 4 speed, 3.25 rear that got 9 - 11 in town, 11 - 15 on the road. I was a lead footed 20 year old. The best it ever got was 17.5 and that was driving 45 - 50 because of a snow storm. Remember, we had 100 octane leaded gas back then. My current '66 F100 (which weighs about the same as a Galaxie) has a 390 4 bbl, 5 speed, 3.50 gears and gets 9 - 11 in town. My 63.5 Galaxie dual quad 427 currently gets about 8 in town. I'm still lead footed. You be able to do better, but probably not what you were hoping for out of your FE without going to fuel injection.
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Old 11-04-2017, 09:43 AM Thread Starter
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Re: Poor mileage

I think my carb is okay, maybe I could improve mpg with a fresher coil? Do coils go through a deterioration stage, or is it just Yes it's good or No it's bad?

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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Old 11-04-2017, 10:43 AM
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Re: Poor mileage

Haven't done a real check on my 390/4v/3.50 rear/auto in a long time, but I think it's not very good. I'm guessing under 10 mpg around town, low teens on the highway.

Problem is that I rarely do straight highway for any real distance. So, I can't really judge.

Weird, but the best gas mileage I ever got with this car was with the car's original 352/4v. The engine was on it's last legs, but, for some inexplicable reason, the mpg went up.

It's nice now having a real 390, but considering my driving habits, the 352/4v would have been just fine.

A 289, IMHO, would have been a little weak pushing a heavy convert.
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Old 11-04-2017, 12:11 PM
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Re: Poor mileage

You can instantly increase your gas mileage by about 15% for free without changing anything just by using Imperial instead of US gallons to do the calculation
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Old 11-04-2017, 01:27 PM
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Re: Poor mileage

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Originally Posted by Eldoon View Post
You can instantly increase your gas mileage by about 15% for free without changing anything just by using Imperial instead of US gallons to do the calculation
Well....there ya go.....but what about $$'s per Imperial Gallon Eldoon??
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Old 11-04-2017, 04:05 PM
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Re: Poor mileage

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Well....there ya go.....but what about $$'s per Imperial Gallon Eldoon??
Well, there you go.... you managed to put your finger right on the one flaw in my theory.......



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Old 11-05-2017, 11:00 AM
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Re: Poor mileage

Hello boys, long time no see 8)

You might want to replace that coil, when the dwell is set like in your accel dist, the coil will work at a standard temperature, if there's varying times over the same drive periods where it will be hotter than other times, then there's a discharge issue likely happening causing the heat build up.

Hope that helps...

And 8 mpg is common, but 10 and 12 is nominal for my 390 FE's I've driven.
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Old 11-05-2017, 07:37 PM
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Re: Poor mileage

My 68 Mustang F/B with 0.030 over 390, mild cam, 4 spd, 4bbl, 3.25 gears got a consistent 10-12 mpg in town. 18-20 hwy.
Lighter than a Galaxie and manual trans helps.

My 66 Galaxie 390 auto 3.00 gears, 4bbl carb got 14-15 mpg in town.

You should be able to get better than what you are.

Check air/fuel ratio to see if carb is rich.
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Old 11-05-2017, 08:35 PM
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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.

Sent from my HTC6545LVW using Tapatalk
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Last edited by Tim C; 11-05-2017 at 08:42 PM.
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