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post #1 of 5 Old 05-14-2006, 06:41 PM Thread Starter
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Angry fuel economy

I have an 83' cj7 with a 258 engine. I have a weber carb upgrade and i get horrible gas mileage. I think i get between 4-6 mpg. Is there anythign that needs to be replaced as the previous owner let this jeep get a little neglected. I read somewhere that replacing the carbon canister for the vacume system will improve gas mileage. Anyone have any ideas??

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post #2 of 5 Old 05-14-2006, 07:50 PM
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Jesus man, I have a 258, 33" tires, weber 38, 3.31 gears, and I get about 14-15 mpg. Four to six is pretty bad. What size tires and what gears do you have in the rear?

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post #3 of 5 Old 05-17-2006, 07:49 PM
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good mileage here

Originally Posted by jeepsarecool
Jesus man, I have a 258, 33" tires, weber 38, 3.31 gears, and I get about 14-15 mpg. Four to six is pretty bad. What size tires and what gears do you have in the rear?

I have an 81 CJ-7 Renegade, my 2 1/2 years of owning it the 151ci Iron duke finally decide to KAPUT! I rebuilt an 81 258 inline 6 back in Nov 05. Now I have a 258 ci I6 with a sr4 and dana300. The rears are 20 and 30 with 4.10 gears. Now the tranny and transfercase including the rear ends are geared for the 151 ci Iron duke inline 4. I have installed superswampers 36x12.50x15's which compensates for the gear ratio. I commute 96 miles round trip to and from work and use 6 gallons of gas a day. That is 16 MPG. I use 30 gallons a week. So kiddo, 4-5 is very lousy. My carb is a single barrel and I only have the air/fuel mixture screw opened one turn.
Good luck on getting better gas mileage, with the crazy price of gas now.
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post #4 of 5 Old 05-17-2006, 08:07 PM
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just check and replace everything.. Dump the stock carb first, go with an MC2100. Then dump the ignition and go with an HEI set up. change the plugs, fuel filter, and air filter.

Another thing often over looked is your brakes! If you have one that is sticking, then it will dramatically drop your MPG. Also, pump them tires up about 5lbs over what it calls for. I run my J10 at 40lbs, and get about 1-2 more MPG when I do. My big GMC runs 75 is all 6 tires. Basically, the higher you pump your tires, the easier it will roll, increasing your MPG.

Another thing is to clean out your Jeep. Get rid of any access weight you don't need. In my work truck, by the end of a month of working, I find myself with about 400lbs of extra tools. Everything from an air compressor to breaker bars, to just general scrap steel. Of course your jeep doesn't carry quite as much stuff, but every lb of extra weight will hinder your MPG, lower your power, and cause things to break easier.

There's a lot of things that you can do to get your jeep running better, and getting better milage. most of the things are super simple, and will cost next to nothing. I've read that synthetic fluids in the axles will give a bit more MPG, along with synthetic fluids in the tranny and transfer case. Mobil 1 is the best I've read about.

Stay away from any of the stupid 'guaranteed to increase MPG' crap. You don't need a tornado, a fuel magnet, of any other type of thing. If they were THAT good, the factory would use them, or something similar, to help sell cars new. Most of them are nothing but a gag.

Good luck, and keep us informed on what you find out.


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post #5 of 5 Old 05-17-2006, 08:45 PM
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1976 CJ7 
Join Date: May 2004
Location: Massachusetts
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just like everyone else says, replace fuel filter, oil change, spark plug+wire replacment, upgrade/clean carb, weight reduction, air filter, all the routine maitenance should increase that mpg....jeez i get about 10-11 and i thought that was bad...oh and also, im a poor college kid, when im skimpin for the week and dont have much funds, i drive very cautiously and see a huge difference from when i have 3/4 a tank and drive how i want to...so in conclusion, maintenance and efficient driving habits...

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