Carbs

I have a 1975 CJ5 with a 304.

When I bought it it had a 4 bbl holley 600cfm on it, and started great and ran well most everytime.


When it would get warm and I'd run it hard, the carb would become very rich and start to overload the cylinders causing them to miss and backfire. So I changed it to an Edelbrock, 600cfm. It runs better, but still rich, and I plan on changing the primary rods soon to lean it out. But now it starts very difficult.


Are there any carb masters still left in this world? Whats the best setup for a 304, should I change it to 2bbl? Doing the math I should only ever need 527 cfm.

304 cuin / 12^3 (cuin to cfm covnersion) * 6000 rpm / 2 rpms per "suck" = 527 cfm theoretical max cfm at no vacuum.

 

All I can tell ya is that I had a Holley on my 304. It ran great in town, but sucked offroad. I found a MotorCraft 2100 on Egay, and it was just the thing.

 

Was your old holley a 2 barrel too? Or did you go from 4 to 2 bbl when you bought the moto?

 

I run a Holley 2 bbl, I think it is a 350 cfm, runs great both on and off road.

 

Personally I think the 600 cfm unit is way to much for a 304 cu in engine, If you could find one Holly made a 380 cfm 4bbl that would be about all the 304 could handle. Actually, considering that a stock engine is at best about 80% volumetrically efficient between 4000 - 6000 rpm even the little 380 cfm 4bbl is possibly to much.
I would bet that a 250cfm 2bbl would excel in the all around performance department for 90% of your driving.
This is just my personal opinion from some first hand experience with large 4bbl's on medium sized V8's in off road four wheel drive vehicles.
Hope this helps.

 

Mine was a 2 bbl. It is still sittin in the garage gathering dust.. Maybe some people like em, but I hated that thing.. It's there if someone wants it..

 

If you've already got the 4bbl manifold, I'd go with a truck Avenger 470 cfm. I can see a stock 304 ever needing more carb than that.

 

Thanks, My bad I thought it was 380. I agree that a small 4bbl properly calibrated will run good on the 304.

 

Ya, I think I will buy an adapter plate and go to a 2 bbl. The jeep isn't a race car, I need more torque than HP. However, what do you guys recommend for a 360 cuin?

 

There's a guy on eBay that sells Motorcraft 2100/2150s for Jeeps. He will set one up for you. Only heard good things about this seller; no personal experience though.

 

I ordered one of them last week, I will let you know how it works out with my split headers on the 258 and HEI distributor, anything has to be better than the 1 bbl on there now. It has run great on the trails but won't get out of it's own way on the road!

By the way, the guy selling those carbs is great to talk to as well as willing to work with you to make sure you are satisfied.

Dan

 

I have the motorcraft 2100 (2BBl) and it works good. Most threads I have read say stick with the stock carb