79 CJ7-tune up and gas mileage suggestions

[Sinister CJ7]

Hey guys I recently purchased a 79 CJ7 that needs alot of love. It was a plow truck and has been sitting for a few years It runs.. kind of rough. A new fuel pump and filter were installed about a month ago, and I plan to do plugs. Im thinking a carb rebuild would be best seeing as I have no clue the real history on this thing. I want to get the best possible gas mileage for this thing(yes I know its a jeep and they are not great on gas). It has a AMC 258 i6 / 4.2l with the 3 speed manual and will see the highway 80% of the time

What im wondering is what carb rebuild kit is suggested?
What other engine parts would be suggested to go over and inspect/replace? It has around 150k on the clock.

I was thinking of swapping out both gear sets for taller gears(2.73) like the later model CJ7s, is this suggested or worth the cost? to gain better gas mileage. It wont be doing much off roading so the loss of some low end grunt wont bother me much. If its worth it, who sells quality affordable gear sets.
Also is there any drivetrain parts that would be suggested to inspect for getting this thing on the road again without to much worry?

thanks

 

[CJ]

Welcome to the site Sinister CJ7! Glad to have you here.

Just about all carb kits are the same - so I would worry about the particular brand.

At 150k I'm pretty sure the engine could use another timing chain. I'm sure it is stretched by now. Also, a TeamRush ignition upgrade will help quit a bit. How much work do you want to do to the engine?

As for the gears, what ratio do you have right now?

 

[Old Dog]

I would do a complete tune up ie. plugs, wires, cap, roter. No tellen when it was done last.

 

[Old Dog]

As for the 2:73 gears, what size tires are you going to run?

 

[Cheepjeep85]

i'd find out what size gears you have then go from there. its a good possibility you already have 2.73 gears, or something real close because you have a 3 speed tranny. i'd pull the diff cover and count the teath, i know its alot of trouble but chances are the gear dope needs changing anyway.
definately do some sort of ignition upgrade that'll get you the most bang for your buck. and if your really serious about it look into fuel injection

 

[IOPort51]

Before you do the tune up check out the TFI ignition upgrade. For the price of a tune up you will bring the ignition system into this millennium. IMHO the TFI is the single most important upgrade you can make to a AMC 258 i6 / 4.2l . You will not be able to compare the before and after but I feel it does more for the engine than any other modification you can make to the engine. The only part that you would not be changing with a regular tune up is the TFI coil, its about $50. This works much better than the HEI and is easier and cheeper. It may help considerably with the rough idle as well.
Easy Fix for Jeep 258 Carter BBD Idle Problem
An interesting article on the carter 2 BBL

 

[LongHorn]

The exhaust is another place to improve your mileage.
If your still running your factory cat, chances are it's overly restrictive
There are free flowing after market one available, depending on local regs.
Also don't think of it as rust, think of it as corrosively lightened body panels for fuel mileage.
Most of your MPG problems are due to the aerodynamics.

 

[IOPort51]

The exhaust is another place to improve your mileage.
If your still running your factory cat, chances are it's overly restrictive
There are free flowing after market one available, depending on local regs.
Also don't think of it as rust, think of it as corrosively lightened body panels for fuel mileage.
Most of your MPG problems are due to the aerodynamics.

corrosively lightened body panels, That is good. I think we can invent a new acronym, CLBP's.:laugh:

 

[kicknjeep]

corrosively lightened body panels, Now I can relate to that

that's the reason for the 2 seater concept

 

[Sinister CJ7]

thanks for the help guys, I was "informed" the car had real short gears(3.xx), which is why I was interested in the gear swap. Is there a way to check without dropping the cover? I plan to run 15" rims and tires similar to whats on it now. I found a set of stock YJ rims in great shape with decent tread tires.
Does anyone have links to a place to get the upgraded TFI ignition system(a known reliable vendor that has good prices)?
What spark plugs would be suggested?

The cars catback rusted and fell off so it has basicly open manifolds. I have 2 cherry bomb resonators with a small turn down(2.25 all the way) I plan to install once the tune up is done, Ive heard a CJ with this setup and it sounds pretty mean but not too loud.

Thanks again for all the help

 

[IOPort51]

I don't believe the YJ wheels will fit, they have a different bolt pattern, 5 lug but smaller circle.
The TFI is kind of a thing you put together not something you buy as a kit.
Motorcraft Distributor TFI Upgrade for the AMC 258
This should help read it thoroughly. and feel free to ask questions.
all you need to buy is the cap, cap adapter, rotor, plug wires and coil.
believe me, it is a very good thing.

thanks for the help guys, I was "informed" the car had real short gears(3.xx), which is why I was interested in the gear swap. Is there a way to check without dropping the cover? I plan to run 15" rims and tires similar to whats on it now. I found a set of stock YJ rims in great shape with decent tread tires.
Does anyone have links to a place to get the upgraded TFI ignition system(a known reliable vendor that has good prices)?
What spark plugs would be suggested?

The cars catback rusted and fell off so it has basicly open manifolds. I have 2 cherry bomb resonators with a small turn down(2.25 all the way) I plan to install once the tune up is done, Ive heard a CJ with this setup and it sounds pretty mean but not too loud.

Thanks again for all the help

 

[Sinister CJ7]

ok, the writeup makes it seem a bit much but nothing I cant handle.
Anyone know how much the swap ending up running them(in parts)?

I know there are diff offsets but I could of sworn i read some where they dont need the adaptors for YJ rims
Does anyone know for sure if they wont fit before I pull the trigger and get the rims and tires?

 

[Old Dog]

YJ rims are 5 on 4 1/2 and cj's are 5 on 5 1/2. so no they will NOT fit.

 

[Sinister CJ7]

thanks, that saved me a few bucks. Maybe ill just repaint the current ones on it and find some decent tires.

any suggestions on the plugs, im thinking NGK or champion

 

[IOPort51]

thanks, that saved me a few bucks. Maybe ill just repaint the current ones on it and find some decent tires.

any suggestions on the plugs, im thinking NGK or champion

I use NGKs all the time, for trot line weights. Bosh or champion, AC is good too. just what ever, I don't think brand will make a huge difference but thats just me. TFI will run about $100 with good parts use the old coil and about $50. The old coil will still work but the TFI coil will work better.

 

[LongHorn]

I use NGKs all the time, for trot line weights. Bosh or champion, AC is good too. just what ever, I don't think brand will make a huge difference but thats just me. TFI will run about $100 with good parts use the old coil and about $50. The old coil will still work but the TFI coil will work better.

I use Champion RN12YC & use a side gap HEI Ing., I'm getting 9-10 mpg with a Holley 4barrel 401 V8. In a 4500lb. 7'6" CJ8 with 38" tires & 4.56 Detroit locker.
It's got all the aerodynamics of a Peterbuilt.

 

[Sinister CJ7]

thats one reason im thinking about not adding much lift to jeep, I think a nice set of larger tires would get me the height I want with out turning it into a square shaped sail on the highway.

 

[LongHorn]

thats one reason im thinking about not adding much lift to jeep, I think a nice set of larger tires would get me the height I want with out turning it into a square shaped sail on the highway.

Even stock they are not exactly slick.

 

[IOPort51]

thats one reason im thinking about not adding much lift to jeep, I think a nice set of larger tires would get me the height I want with out turning it into a square shaped sail on the highway.

The two front tires offer about 6 square feet of air resistance of which half is trying to go twice as fast as the rest of the forward surface. And as a wise man has said a Jeep has a forward profile similar to a 4X8 sheet of plywood. I have thought about a wing on the front bumper deflecting the air over the wind shield. I am not generally one to worry about appearances but I can find no way to make a Canard look like it belongs on a Jeep.
:barf:

 

[Cheepjeep85]

go with the e3 diamond fire plugs you won't regret it.