15 mpg in 200

[67mustangat16]

So I have a straight 200 that is completely stock. I have driven it for a couple weeks and realized im only getting about 15 mpg. Ive done all the normal tune up stuff. New distributor, rebuilt carb, gap is perfect. Only thing going on is i have an exhaust leak in the manifold, but I don't think that would affect it that much. I was just wondering if anybody has had this problem or if there is anything else i can do?

 

[bubba22349]

Have you done a compression test yet to find out the condition of your engine?

 

[xctasy]

So I have a straight 200 that is completely stock. I have driven it for a couple weeks and realized im only getting about 15 mpg. Ive done all the normal tune up stuff. New distributor, rebuilt carb, gap is perfect. Only thing going on is i have an exhaust leak in the manifold, but I don't think that would affect it that much. I was just wondering if anybody has had this problem or if there is anything else i can do?

How steep is your journey, is it cement freeway, is it 80 mph, and is it short run?

Mine has 1981 200 with early small chamber head, 1.3" log and its operated over ambling tar macadam over the sharp relief that is :NZ: New Zealand. Diff is 2.73, C3 3-speed auto, 2650 pounds, but we carry 3100 pounds ( My 150 pound 20 year old son, 50 pounds of texture sand, 5 gals of 87 octane, computer, printer, extra 11 plate battery, special suspension equip ment. And a couple of loopey lights on the roof).

Around town, 11.8 US miles per gallon (its steeper than San Fransisco and is short run and used in traffic for each day), on the open road, 16.6 US Miles per gallon (ave speed 55 to 65 mph). Stock timing, new plugs, all emissions gear.

 

[bmbm40]

Do you have an automatic or manual? Is it mostly city driving?

 

[170-3tree]

All of the above questions?
A automatic will be bad for mileage as will stop and go driving as well as excessive speed on highways.
Did you set everything to specifications or did you use some of the simpler mods found all over this site?
I would suggest picking up the falcon six performance handbook. It has a lot of modifications and information in it divided in sections from free to stupid expensive. A lot of the free ones will net both more performance and usually better mpgs.
You might put your location in your info section because a lot of the time that can help us help you when issues can be location can be a matter of issue.

 

[MPGmustang]

check the vacuum canister on the distributor, if good, advance the timing 3-4 degree's

 

[thesameguy]

Now that my car is running very well all the time, I've been able to do a little mileage calculations. I would definitely support the notion that stop & go + high speed freeway is really hard on fuel economy. Mid-teens for me. My work commute, however, which is 8 miles of pretty constant ~40mph travel I can see mid-20s. Pretty crazy variation! I've got a essentially stock 200 (Pertronix+coil, slightly larger exhaust) running on a Holley 1940 connected to a 2-speed FoM. Not a formula for high mileage. I've got static timing set at 12 degrees, with an LoM distributor connected to a non-LoM carb, and run nothing but 91 octane gas. I've been driving in dry high '80s/mid '90s weather - a cool summer for Sacramento! Once the forecast calls for '95+, I drive something with AC.

 

[67mustangat16]

Manual, mix of city and high way about half and half 30 miles a day. I set everything to the specifications and no i haven't done a compression check and I'm pretty sure my timing is advanced. I determined that last night so I need to change that. The journey is flat.

 

[cisco170]

viewtopic.php?f=76&t=67087 i made a rear end change 15mpg to 23mpg 170eng 2sp. cheers

 

[67mustangat16]

compression psi from front to back pistons 1. 145psi 2. 155 3. 155 4. 150 5. 150 6. 150

 

[CZLN6]

Howdy 67 and All:

15 mpg all-around is a little low. Where are your located. Critical issues are elevation and gas formula in your area. I'm assuming you have your engine in good tune and you have the tires all aired up to 32 - 35 psi, no brakes dragging and wheels are all rolling in the same line. Also that you are not carrying around alot of unnecessary, heavy stuff. How do your spark plugs look? Have you opened up the gap with the PetroniX Ignitor? .045" is a good place to start. Depending on your elevation and gas you can gain some efficiency by adding another 5 degrees of advance to the initial setting. That's straight out of the '67 shop manual. I think I recall that stock setting on a '67 200 with a manual trans is 6 degree BTC. You should be able to go to 10 to 12 degrees of initial advance without causing pinging.

Also make sure your automatic choke is set a mark or two toward lean. Just enough choke to get a cold start and run. Set your idle as low as you can go. Adjust the low speed air screw to the highest rpm at the slowest idle setting. Make sure the accelerator pump lever is in the "LO" position. The two positions "HI" and "LO" are held in place with a roll pin. Simply remove the pin and reposition if necessary. Cars sold in winter states typically have the pin in the "HI" position.

Finally avoid high rpm driving, stop and go traffic, and never idle your engine. Drive easy, but be safe.

Your compression test showed good numbers for a veteran engine. A leak in the exhaust will not typically effect mileage. It could be dangerous to your health and may cause valves to burn prematurely.

Keep accurate records with miles covered and gallons consumed. Tests of less than 100 miles on the odometer will tend to be less informative. Always gas up at the same place, at the same time of day and in the same way. The more objective you are in record keeping the more accurate your results will be.

That should give your some places to look for a little better mileage. Keep us posted on your progress.

Adios, David

 

[bubba22349]

X2 on tune settings also check condition of the carb that float level is set right! You might also confirm that the odometer is reading correctly i.e. Check the mile markers or use a GPS.

 

[67mustangat16]

I'm at sea level in Washington state. The gas formula has 10% ethanol in it which im sure doesn't help. My spark plugs are a tan color which my manual says is good. The gap i will definetely try and im checking my timing tonight. The Carburetor is set to low. So setting the timing to 10 or 12 is good?

 

[bubba22349]

Try 12 and see if that works, it should be OK at sea level

 

[CZLN6]

Howdy back:

Don't forget the lowest idle, highest vacuum reading/rpm from the low speed air screw and the leanest choke setting.

One more last thought. Make sure your vacuum advance canister is working. IF it is it will add additional advance at steady highway speed, for another little boost in mpg.

The dense, moist air along the Washington coast. If 12 degrees of advance causes any pinging, try 10. Keep reducing the initial setting til you get no ping. 10% ethanol in the gas is not the problem. It is usually the oxygenated formulas like Calif uses in some areas. If plugs are tan, your A/F ratio is in the right ballpark.

Keep it coming.

Adios, David

 

[MPGmustang]

all these reply's are great, and are heading you in the right direction,

?? when is the last time you rebuilt or cleaned the carb? and is the choke working properly when engine is cool? the last thing I would suggest is to unlink your throttle linkage at the carb, and move the carb throttle by hand and see if there is any odd play. it could/might just be a worn carb.

compresion and plugs sound spot on, what's your rpm at idle? with a manual and stock engine you should be able to get a nice 650rpm idle (500rpm idle is unrealistic with the new gas)

 

[69.5Mav]

All the points raised are very good.

One thing I have not heard mentioned is leakage especially from yhe rubber gas lines.

There are at least two. One at the carb and one at the tank.

Also check to make sure the tank and steel lines are not leaking.

Check the carb end of the system with the engine running to detect any pressure leaks.

The next thing I would check is the tires. this can sneak up on a person and cause a loss of mileage.

Lastly you need to have a matched carb/distributer. The Load O Matic (LOM) distributer should be used with a carb with a spark control valve and a non LOM distributer should not be used with aspark control valve carb, if you have this combo use manifold vacuum for the distributer.

 

[xctasy]

I use a database for my fuel consumption, from my RWDS program

(My car is a Japanese Domestic Market Mustang, which reads in kilometers, and since New Zealand is a British Colony, we use Imperial MPG, not good ol boy US Mpg)


Start to End Km Liters Imp MPG US mpg
62008-62163 155 33.17 13.2 11.0 Around town
62163-62307 144 28.64 14.2 11.8 Around town
62307-62407 100 14.71 19.2 16.0 Around town
62407-62631 224 33.80 18.7 15.6 dunedin-OMARAMA
62631-62929 298 42.36 19.9 16.6 Omarama to Dunedin
62929-62981 52 12.49 11.8 9.8 around town plus ideling
62981-63037 56 10.69 14.8 12.3 Dunedin to Milton
63037-63297 260 36.70 20.0 16.7 Milton to Beu mcnab then Balclutha Light on 63262

The details show that today was the first time ever I've gotton more than 16.7 mpg. I'm still working through the fuel control valve, EGR and oxygen sensor of my 50 th State California spec Mustang.

Tomorrow, I'll hook it on the engine analyser.

 

[67mustangat16]

Well I believe I may have found the problem. I checked my timing and found it was atleast 15 degrees below tdc. I adjusted it to 12 degrees. And have already noticed an amazing difference in power and hopefully mpg.

 

[67mustangat16]

Yup I'm getting about 26-27 mpg now. Thanks for the help.