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-   -   7 miles per gallon ?!?!?!?! (http://www.ifsja.org/forums/vb/showthread.php?t=38519)

jode 03-10-2004 07:23 AM

I have been tracking my fuel usage and trying to use a light right foot for the last month to see if it makes enough difference to make it worthwhile to not always be mashing the gas. I just ran some numbers on the last three tanks…I am averaging 7.15 mpg :eek: I had no idea it was this bad. I have a stock 401 that seems to run fine, with performer intake and Carter AFB. I “tuned” the carb myself with a vac guage as best I could (I am no pro at this) and thought I kinda had it dialed in. However, it may be running a bit rich (based on the fact that the exhaust smells a bit rich)
So my question is, what specific things should I look for/pinpoint to try to get my mpg up. I know I am not going to get 15 mpg, but 10 would be nice :rolleyes:
At this point, I am thinking of taking it to this mechanic I know :eek: handing him $50 cash and saying spend an hour tinkering on the tune for this thing OK?

JERSEY JOE 03-10-2004 07:52 AM

Did you buy the AFB new? If not get a tuning kit and replace the jets and metering rods with the stock setup. I had a similar setup on one of my 360's. The metering rods have a large effect on fuel economy, also there are springs for the rods that should be checked. For stock settings try the Edelbrock or Carter website.

Beyond that check that the vacuum chamber on the distributor is good. Hook a hose to it, it should hold suction AND look at the breaker plate while you apply suction. It should move. Next make sure that you have the hose going to the distributor set to ported vacuum NOT manifold vacuum.

BK 03-10-2004 07:53 AM

Come on now, these things are "da bomb!". Gas mileage is low and what fun is it if you don't mash the gas now and then? :D

jode 03-10-2004 08:01 AM

Oops – about that dist advance line…forgot to mention that I broke off the vac nipple (crappy plastic Prestolite dizzy :mad: ) That line is plugged. Makes you wonder though, could no vac advance be causing that much of a gas mileage decrease?

jode 03-10-2004 08:02 AM

Quote:

Originally posted by BK:
what fun is it if you don't mash the gas now and then? :D
Usually I do....which is why I started metering the gas consumption and going easy on the skinny. I wanted to see if it really made that much of a difference...

pb 03-10-2004 08:04 AM

I had been getting 7 mph for awhile (since I bought the wagon). I just replaced the wheel brake cylinders this weekend. I haven't checked the mileage, but she runs a lot better and coasts on the road.

I had looked at everything until one day I tried to push it forward 6" to get the garage door to shut. It wouldn't budge. The back driver's side brake was seized.

[ March 10, 2004, 02:05 PM: Message edited by: pb ]

joe 03-10-2004 08:18 AM

Quote:

Originally posted by jode:
Oops – about that dist advance line…forgot to mention that I broke off the vac nipple (crappy plastic Prestolite dizzy :mad: ) That line is plugged. Makes you wonder though, could no vac advance be causing that much of a gas mileage decrease?
It's possible Jode. When you do put your foot in it w/o vac adv the fuel is doing nothing to make you go faster till the mechanical adv catches up. I would fix that first(by throwing the presto-no-light dizzy away) and then go from there. Granted both my trucks were/are only 360's but both got 10-11mpgs running stock 4.09 gears so yours should at least be crowding the double number range.

[ March 10, 2004, 02:19 PM: Message edited by: -joe ]

jode 03-10-2004 08:23 AM

Good point - I should have a "new" Presto crap dizzy to throw in there by this wknd....then I'll remeasure mpg and let you know...frankly htough, I could never tell the difference :eek:

kreb 03-10-2004 08:24 AM

i just did some number crunching on my own and my 8mpg is not going to cut it. the truck runs like a top and no real problems. but the mileage is not working. the carb is rebuit and the plugs look fine. keep us posted

benjamin

Rich 89 Gr. Wag 03-10-2004 08:26 AM

11-12 mpg for me with the 360 and the Motorcrap carb.

carrotman 03-10-2004 09:04 AM

A Prestolite ignition without a vacuum advance is like towing a parachute behind your Wagoneer. When I replaced the Prestolite with an HEI on my 76 360, the vapor lock, stalling, and hard starting disappeared. I was always blaming my carb, fuel pump, fuel filter, gas tank, and gas lines. Still get only 10 MPG, but it was worth it.

jode 03-10-2004 09:09 AM

Well, I am getting the "new" prestolite this wknd, but i should have funds for the complete Motorcrap/TFI swap within a few months...that will be nice. I can turn my 31s as is, if this TFI is all it is cracked up to be, I oughta be able to really roast em after the swap heh?

billyrb 03-10-2004 09:25 AM

Jode, that vac. advance is #1 to fix. Then check the mixture and tune it a little bit leaner than what you have (if you smell a lot of gas when running). What gears are you running?

If you have 2.72's through 3.31's, with your tires and 4bbl, you should be getting around 10-12mpg. average if you do some highway or straight driving and some traffic driving, with a regular foot (in it about 15% of the time).

Gawdzilla. 03-10-2004 09:30 AM

vacuum advance really only helps when you're not on the gas (when the engine is under very little load)...so when you're cruising or coasting you develop more vacuum. more vacuum gives more advance. More advance allows you to run leaner, etc.
if you do a lot of stop and go driving tho, forget it. your mileage is gonna suck.

jode 03-10-2004 09:42 AM

Ah hah...that makes sense Gawdzilla - cuz if you have a vac guage hooked up to the manifold, vac plummets when you hit the gas, vac can only be sustained when you are cruising...it makes sense.
I drive to and from work in the wag, approx 5 stops per 10 miles - never exceeding 45 mph
Maybe that isn't really helping me either huh?

I'm going to be doing some freeway driving this wknd (although I never go over 60 anymore what with the vac advance non-functional and all) and although I will be towing a trailer, I'll track the mileage to see what it looks like.
Thanks all

Gawdzilla. 03-10-2004 09:50 AM

if you wanna you can set the mechanical advance to some mid point you're happy with- like 18 - 20 and be done with it. Check the hotrodding boards for the way those guys do it. It's not uncommon- as I understand it the ONLY reason for vac advance at all is to improve mileage via the process I described. And if you're pulling a trailer you won't get any meaningful numbers unless you pull a trailer all the time. Have fun!

89grand 03-10-2004 10:29 AM

I don't even have my vacuum advance hooked up because I get a lot pinging when it is. I've seen no bad side effects.

1studiac 03-10-2004 11:00 AM

Quote:

Originally posted by Gawdzilla:
vacuum advance really only helps when you're not on the gas (when the engine is under very little load)...so when you're cruising or coasting you develop more vacuum. more vacuum gives more advance. More advance allows you to run leaner, etc.
if you do a lot of stop and go driving tho, forget it. your mileage is gonna suck.

I dont think that is the way it works, if you run without a cto then you need to hook the dizzy up to ported vac, ported vac increases as rpm's increase. The only time the dizzy is on manifold vac (which is the vac that drops when you step on it) is when the engine is warming up as it needs the advance to help keep it running while cold. If you hook that dizzy up to ported vac I would almost guarentee you see a couple more miles to the gallon, like said it's like pulling a chute behind you without it. I don't know what my mpg is but it's got to be pushing 13 or 14 and it was somewhere just over half that when I had my vac for the dizzy hooked up to manifold vac by mistake.

89 grand sounds like your getting to much advance. What is your timing set at? Could be a weak set of springs on your mech advance so when you step on it and with the addition of the vac advance it's getting to much advance to quick. Springs are cheap, that's what I would try.

[ March 10, 2004, 06:18 PM: Message edited by: 1studiac ]

PlumCrazy 03-10-2004 12:26 PM

:eek: I thought Tera was bad at 9.3mpg before the motor crapped out...I haven't checked with the new motor until I get the guages in and broke in good.

Wayne S.

Sitting Bull 03-10-2004 12:52 PM

Quote:

Originally posted by 89grand:
I don't even have my vacuum advance hooked up because I get a lot pinging when it is. I've seen no bad side effects.
----------

This is typically a bad return spring on the vac advance. I beleive there is an upper and lower spring, both may need replacing. Every actual FIX I've seen for the dreaded ping has been related to these two springs.


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