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I have a 73 that is giving me way too little miles to the gallon. it gives something in the range of 15 to 20 miles to the gallon. i recently got the carb rebuilt, and gave it a tune-up, but didnt seem to improve much. Any suggestions/comments??

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LUV is...

There's no easy answer. My stock '75 got 31-32mpg with the stock Hitachi carb.

The best bet is to simply go through it and do a major maintenance on it: adjust valves, remove distributor and check centrifugal advance springs for free and easy movement [put a drop of oiil on pivots], apply vaccum to vacuum advance hose by mouth and make sure points plate moves easily and smoothly and full advances, remove & check EGR by applying vacuum and watching for movement on plunger. Carefully remove plug wires one at a time while engine's running to see if you have a cylinder misfire.

Set timing to factory specs and then advance it a few degrees until you get pinking, then retard it just until it stops pinking. Adjust carb, remove catalytic converter and toss it, check all electrical connections, make sure brakes aren't dragging, keep tires aired up to maximum on sidewall, etc.

Doing it that way you know exactly what condition everything is in and can have more peace of mind also.

My stock '78 got about 17 on a good day. Part of it is the gearing, I'm surprised to hear JimmieD was able to coax that sort of mileage out of the 4 speed. The Hitachi carbs are not known for tunablility, but rejetting may deliver more mpgs. Not my area of expertise, but I've had several old Ramblers with 3.2 liter engines and one barrel carbs that returned high 20's with a couple of simple jet mods...

I'm curious what sort of mileage everyone else is getting...

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"If we did the things we are capable of, we would astound ourselves" - Thomas Edison

from 25 to 28 on mine (weber , header , cam , 2.5 exaust)

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My old but now gone Luv...

ctman> are you still running the 4 speed? I thought you changed out the rear gears too?

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"If we did the things we are capable of, we would astound ourselves" - Thomas Edison

still a 4 , never put the 5 in but its all here ready to go... maybe some day the rear is now back to 4:10 i had 4:56 in but thought it was a 4:10 that only lasted about a month , wouldn’t go very fast and speedo was way off

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My old but now gone Luv...

You guys are all lucky. Mine is stock and gets 10mpg. It didn't use to bother me when gas was 99¢ per gallon. My Dodge Ram Quad cab gets better mileage.

I went with slightly bigger tires, than the stock ones, and 15" rims. How would that affect my gas mileage?

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LUV is...

It is equivalent to getting higher gears (numerically lower). It should lower your RPMs in 4th gear at the same speed as before. There are online calculators that will tell you. If yours still has the stock '73 drivetrain, it is a 4.56 rear and is quite buzzy on the freeway (65 feels like the end of the world for me). Larger tires should help that. So it may help your mileage on the highway (probably very little), not sure about in town.

I am getting 30-35 mpg header,5 speed,1 inlet duel outlet flowmaster,and i use 93 octaine fuel

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my truck got about 20mpg its a 1974. with a outlaw weber on it.

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4.3l V6. 5 speed MT 2.55 in the back.

To check dist, remove cap and lightly turn rotor. It should in the direction of rotation and spring back smoothly. Put a vacuum pump on the vacuum advance and pump it up and you should see the breaker plate move. You also can use the pump to check the EGR. With engine running pull a vacuum on the EGR valve the engine should stumble and almost die, some will die. Run a HOT compression test to check the cylinders. They should be within about 10 pounds and over 100. A cylinder with less than approx 70 pounds usually will not fire at an idle. Check for vacuum leaks, spray some water around the connections. Also check cam timing if the above doesn't help.
The last cause of high fuel consumption is the weight of the drivers foot and time used deciding when to shift to the next gear.

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The light at the end of the tunnel, may just be a train coming!