Poor gas mileage with 225

Mine with headers and a dual point still manages between 14.5 and about 15.2 just depends on the weather and road, thats with 3.73 gears and 31's. I would look to the carb and possibly rejetting.

 

start with the basics:
compression test
leakage test
vac reading at idle
post the results

 

Make sure the HEI is timed correctly (vacuum advance is correct/has appropriate advance curve?)

 

I get 13-14mph with 4.27 gears and 31.5's.

 

Man - I would love to get 14 mpg. My all stock 225 is getting 11 mpg. Scratching head - maybe I need to look a little deeper.

 

Better than 15 mpg (regularly) has been rumored around here a few times, but I think those people are bad at math.

 

Refer to post 8....

 

I would expect a lot depends on how you drive, and what your comfortable top speed is. The wind resistance between 55 and 70 mph increases 62%... from 18 to 14 mpg is only a 22% drop.

 

Your cj7 with a 302 has fuel injection and an overdrive which helps alot, not to mention its a much more modern engine.

 

The initial block design is about the same age but the HO heads make it at least 20 years newer in design. But you're right either way your pushing a brick, but I dare say the cj7 has slightly tilted windshield which would help some.

 

I got about 15 MPG for years with a single barrel :v6:.
5:38 with warn OD and 31 in. tires.

 

Billy, maybe Dave puts his foot in it more now that the headers (and I presume free-flowing exhaust) are present?

Headers are supposed to slightly lean out the mixture by the "extraction" effect, which is what I think he's talking about. I think that's actually less dilution of the next fuel-air charge by low-O2 exhaust gas, so there's more O2 available.

The major effect is supposed to be an increase in volumetric efficiency, since the low-restriction exhaust means that the cylinder is closer to atmospheric pressure at the end of the exhaust stroke - no residual pressure to prevent the entry of the new fuel-air charge. You're supposed to compare the spark plugs before and after to track the mixture change, but it would be worthwhile to look at the plugs now.

Conventional wisdom says that headers are the only performance upgrade that also provides an increase in mileage. The headers might change the mixture, but I'd think with proper tuning you should get the same power from less fuel. A change in driving habits would easily wipe that out though.

hth!

 

I was getting 10 with 31s and 5.38. Now with 31s and 3.73s i am getting 15-17. I have petronic hei upgrade and headers.

 

Ok Gentlemen, Thanks for the responce. I was getting 16+ mpg, with dual exhaust and stoch headers. The jeep runs OK? for the most part. I think that my carb is SOOOO old that rejeting is not an answer, that is why I am puttind on a new remanufactured 2 Jet. I am worried about the basics, vacuum, compression, and leak test, it means that I will have to rebuild the motor. This weekend the carb and intake gasket go in to the motor. I will post after that!
Thanks Everyone