Getting MPG down

[duodec]

My '71 with 2.x rear gears averaged 16MPG in mostly city and short (5-10 mile) freeway runs in Las Vegas, on leaded premium.  About 1.5MPG less on regular.  This was pre-reformulated gasoline, no ethanol.

However if you live in an area where the EPA foists off "reformulated" gas, or your politicians buy farm votes by mandating diluting gas with ethanol, you will automatically lose a measurable amount of mileage.  Although I don't have more current measurements on the Challenger, both my 1990 Dodge W250 and the current Jeep Liberty lost 1.5 - 2MPG to gasohol versus straight gasoline.  The Jeep loses 1.5MPG in the winter with the EPA 'winter blend' crap, and the W250 went from 12MPG in the summer to 6MPG (!) once we had to start buying the winter crap gas here in chicagoland (and jumped right back up to 12 when we traveled and could get real gas elsewhere).

'73s had a vacuum delay in the feed to the vacuum advance.  Is it working properly?  Some (the manual is not clear) also had a bypass that would route manifold vacuum to the vacuum advance if coolant temp got too warm.  There's also an EGR valve.  How's it working (is it even working)?

If the timing tweaks and other fixes don't make a difference, try a different station.  Try premium if you are currently using a lower grade.  If you are using gasohol, try finding a station that sells real gasoline.

[72bluNblu]

If I remember right tripple-green is in orange county CA, and would be running the same fuel I am in northern CA. CA gas is surely not the best for anything (except, maybe, smog production), but my numbers are still over twice what he's getting. Good point on the vacuum and EGR though, I know my vacuum hoses all had leaks...

[318Sebring]

1972 Satellite Sebring
318 / 904 auto
Dual exhaust with flow through mufflers.
LD4B intake with a Carter 625 on top.
Luanti voodo cam 60401 203/220 @ 050 .454/.454
Electronic ignition . Orange Box
Windage tray. ( Yes I have one )
8 3/4 rear with 3.23 open

Recent cam instillation and tune up by chryco physco
I get 13 mpg ( US ) around town and 17 mpg ( US )   highway takeing it eaisy.
But who takes it eaisy. 

[duodec]

If I remember right tripple-green is in orange county CA, and would be running the same fuel I am in northern CA. CA gas is surely not the best for anything (except, maybe, smog production), but my numbers are still over twice what he's getting. Good point on the vacuum and EGR though, I know my vacuum hoses all had leaks...

I don't know if its still the case, but when reformulated gas first came out, a lot of cars with older rubber components were severely impacted; the rfg would eat away at the rubber parts, causing both leaks and also letting little black rubber crumblies clog up the fuel filter (or worse get into the carb if there was rubber hose between the filter and the carb inlet).  The solution recommended at the time was to replace the older hose with fuel-injection rated hose, and look for a carb kit that included either rfg or alcohol-resistant rubber parts (accel pump, plastic floats, etc).  The RFG would also soak into the floats (I think for a while some floats were made out of a structural foam; they were not hollow) and keep them from closing the float valve, pretty much like a metal float that had sprung a leak.

If there are real old original rubber parts in the fuel system that might be worth a look to.

This is all going from memory; there was a lot of discussion about this on the GEnie auto boards, and later the MML, as the crap gas got forced onto the market.

[TRIPLE-GREEN]

New filter in the original air cleaner.
New Plugs and wires. about 700 miles ago- Checked and run normal - no build up color is good.
Ign was set to top dead center due a dope at Napa saying that was the stock position.
Stock rear end gears


The car was run for some time way to rich. Is there a way to reduce the amount of carbin build up without pulling the motor apart?

I can see I may have a few things to do and retry. Based on my last tank of gas I think I am running right around 7mpg. But that car is only run 3-4 miles at a time. I have a bad chock on a carborator that honetly sucks. So from your advise and a few other things I think that is my largest problem.

What about this intake I was going to put on. It is a stock 1980's 340 duel plane 4brl intake that will have a new 600cfm carborator on it. Am I just looking for more problems with this intake? The old one is a stock 318 single plane 2brl intake with a really old carb. What can I do or should I do with this set up. Is it a good idea to change it to the new one? I also plan to add the duel exhaust shortly after.

[cudaguy71]

Before I started my restore my 73 baracuda 318 w/904 was getting 15-16 city, 18+ hwy.  It has a 500cfm Holley 2-bbl, cam from a 340, 3.55 gears, & headers.  Timing was 10 @ BTDC

[TRIPLE-GREEN]

I don't know if its still the case, but when reformulated gas first came out, a lot of cars with older rubber components were severely impacted; the rfg would eat away at the rubber parts, causing both leaks and also letting little black rubber crumblies clog up the fuel filter (or worse get into the carb if there was rubber hose between the filter and the carb inlet).  The solution recommended at the time was to replace the older hose with fuel-injection rated hose, and look for a carb kit that included either rfg or alcohol-resistant rubber parts (accel pump, plastic floats, etc).  The RFG would also soak into the floats (I think for a while some floats were made out of a structural foam; they were not hollow) and keep them from closing the float valve, pretty much like a metal float that had sprung a leak.

If there are real old original rubber parts in the fuel system that might be worth a look to.

This is all going from memory; there was a lot of discussion about this on the GEnie auto boards, and later the MML, as the crap gas got forced onto the market.

That is a good point about the gas. This car is all factory. Very little has been modified over the years and the car was prize maintained by my grandmother who would put the car before anything else in her life. I will see if I can take some pics it is worth seeing. I want to keep it stock, but I just can't gather the strength to do it. I will only be making small bolt on changes to improve it but I wish it was in worse condition just so I could go crazy with it.

Thank you guys for the help. It is so nice to be able to get some answers within a few minutes by some people that really know what I am talking about.

[318Sebring]

What about this intake I was going to put on. It is a stock 1980's 340 duel plane 4brl intake that will have a new 600cfm carborator on it. Am I just looking for more problems with this intake? The old one is a stock 318 single plane 2brl intake with a really old carb. What can I do or should I do with this set up. Is it a good idea to change it to the new one? I also plan to add the duel exhaust shortly after.

With a new 4 bbl dual plane intake a new 600 carb and dual exhaust you will get better milage and performance
A Win Win. If you have a really old 2 bbl carb that could be most of your problem.
My 318 mpgs did not go up to much after the 4bbl and intake , but it ran MUCH better . My right foot got heavyer.

[71chally416]

The 340 Intakes are larger than the old '70 318 ports, so you'll end up with a bad mismatch at the head. You need an Intake made for the 318 like an LD-4B.

The guy at NAPA gave you the right timing figure. My Chiltons manual for the Barracuda-Challenger lists the timing at TDC for the '69 to '72 318 (It doesn't have the 73 listed) You can run it as far advanced as you can as long as it doesn't ping, but I'd be careful how far you advance it. Remember you have the old non-hardened pre-unleaded fuel exhaust seats and it's real easy to burn an exhaust valve without leaded gas. Leave it in drive while you turn it off and it won't after-run.

Supposedly some types of gas clean the carbon from your motor while you drive. 

From what you're saying I'll bet most of your problem is just the choke and old carb. That old single plane Intake isn't the best design either for best mileage. The factory 2 bbl dual plane is much better. I doubt that a 4bbl of any kind will get better mileage than a properly working 2 bbl unless you drive it very carefully, but a small 4bbl with dual exhausts will make it run 100% better.

[Bullitt-]

Whenever I've used Lucas fuel treatment in our old vehicles they seem to run smoother afterward.
If your only driving it 3-4 miles at a time that could explain a lot.....need to go for a nice long trip & "BLOW OUT THE SUT" as Grandaddy would say.

[71chally416]

THIS is the Intake I would use with 318 heads.
http://cgi.ebay.com/ebaymotors/EDELBROCK-CHYSLER-LD4B-273-318-340-360-INTAKE-MANIFOLD_W0QQcmdZViewItemQQ_trkparmsZ72Q3a552Q7c39Q3a1Q7c66Q3a2Q7c65Q3a12Q7c240Q3a1318QQ_trksidZp3286Q2ec0Q2em14QQhashZitem250284402822QQitemZ250284402822

[heminut]

This is the best method I've found for cleaning carbon out of an engine. First, if you have new plugs you should probably pull them and put an old set in although this procedure has never caused me any problems with the plugs. You will also want to do this outside, NOT in the garage as it will make a LOT of smoke! Remove the aircleaner and then start the car up. Take a quart of cheap transmission fluid and start pouring it down the carb (this is were the smoke comes from!). You will have to hold the throttle open and pour the tranny fluid slowly to keep from killing the engine. The last bit of fluid should be poured in fast enough to kill the engine, then shut the ignition off and let the car sit for about 30 minutes. Start the car again after it has sat, and pour about a pint of water down the carb in the same manner as you did the tranny fluid but don't kill the engine at the last. After you've run the water through take the car out for a drive and run the RPMs up a few times. I guarantee if you have a carbon buildup problem this will clean most if not all of it out. Since it was your grandmother's car it probably does have some carbon buildup.

[318Sebring]

THIS is the Intake I would use with 318 heads.
http://cgi.ebay.com/ebaymotors/EDELBROCK-CHYSLER-LD4B-273-318-340-360-INTAKE-MANIFOLD_W0QQcmdZViewItemQQ_trkparmsZ72Q3a552Q7c39Q3a1Q7c66Q3a2Q7c65Q3a12Q7c240Q3a1318QQ_trksidZp3286Q2ec0Q2em14QQhashZitem250284402822QQitemZ250284402822

 

I have one on my 318. Very Nice.
Note the crack on the carb bolt hole.

[71chally416]

I wouldn't worry about that crack. Anything made of aluminum can always be welded.

[TRIPLE-GREEN]

This is the intake I was going to use....




I work in a hot rod shop and can get a new edelbrock but the reason I went with this idea was I wanted it to remain looking stock. Also the intake was $60.00, after the paint and the sand blasting.