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Discussion Starter #1
I have a 90 yj with 258ci in it. Has Clifford intake and headers and no cat. Wanna change from 4bbl to a 2bbl, should I just go with bigger cfm?
 

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If the engine is fairly stock the 350cfm will be more friendly and offer more low end control.
The 500cfm is better suited for a small V8.
 

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Go to Holley.com and check into their "carburetor selector guide". Answer a few questions honestly and they will provide you great choices. Why would you buy that intake system and not go with a small four barrel? You would probably get much better gas mileage because you would be running on your primaries most of the time, except when you were on the highway, or punching it.

Take care,
 

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Go to Holley.com and check into their "carburetor selector guide". Answer a few questions honestly and they will provide you great choices. Why would you buy that intake system and not go with a small four barrel? You would probably get much better gas mileage because you would be running on your primaries most of the time, except when you were on the highway, or punching it.

Take care,
agreed..the front 2 barrels on a 4 barrel will normally get a lot better mileage than the larger barrels on a 2 barrel
 

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if you really must change I'd go with the 350. but as others have said you will be much happier with a holley 4bbl. look for a 390 cfm. I run the offenhauser manifold with a 40 year old holley 470 cfm and get alot better milage and performance than when I ran a weber. but I found a deal on a 390 and will be installing it next week, hope to do even better.
 

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Like it was said above, the idea of a 2bbl isnt going to give you more MPG.

I run an Offenhauser intake which is basically identical to your clifford intake, and its on a 4.2L 258 C.I.D. I have had a MC2150 on it, and an Edelbrock performer 600cfm 4bbl. And a Holley 750cfm double pumper, but it currently has a Holley 390cfm 4bbl. That carb seems to perform the best. Its the easiest to adjust, and seems to stay in adjustment better than the others as well.

I am getting somewhere in the mid teens (15-17) for MPG as long as i keep my foot out of the secondaries. (which isnt often). The primary holes on a 4bbl are smaller than the 2 holes on a 2bbl, which means less gas to get the same reaction. A 4bbl is always easier on gas than a 2bbl because of that reason.
 

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Discussion Starter #8
I'm getting 10 mpg. I had to tune and tune mostly giving more fuel to fix hisitation/lean backfire under medium to heavy acceleration. I'll try a different Hg power valve (has 6.5? now) ill try 10.5 and reducing jet size. Maybe go 50cc accelerator pump?
 
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