Carburetor to buy

[Tison78_CJ5]

My carburetor is worn out. It is the original on my '78 CJ5 304.
I am building another 304 for my Jeep, but it won't be done for several months.
I have a high rise for it, no carb yet. It takes a 4 barrel.
The 304 in my Jeep is the motor craft, 2100, 2 bbl.
Can I purchase a 4 bbl. Holey, about a 500 cfm, and use it on my old engine?.
I want to keep from buying two carburetors, and be able to play during summer.

I am doing a rebuild on my motor craft, but last one only lasted 3 weeks.

 

[PoliceMonkey161]

Hey Tison,

If you look closely at the side of your 2100, it will have a small circle with a number engraved in the center. This is the venturi size, using the list below you can estimate the CFM it is currently set up for. I'm not an expert with Holley, but I believe you can jet them down a size or two.

.98=190
1.01=240
1.02=245
1.08=287
1.14=300
1.21=351
1.23=356
1.33=424

 

[Tison78_CJ5]

Thanks, that is helpful. Mine is the 287 cfm.
I'll work from that.

 

[Tison78_CJ5]

Well yesterday I rebuilt my distributor, the slinger weights were flopping around. I just knew I had found my problem.
Wrong, no change. Last night I pulled the carb off. Cleaned it completely, 3 cans of cleaner, and my Dremel with a wire brush. It looks new. Really I found no problem with it. I also replaced the fuel filter, and put a bottle of additive in the tank.
So far it is much better, but it still jumps some.
I am starting to think maybe bad gas?
Beats me, I'm going to put some miles on it, and see if it clears up.

 

[69jeepcj]

I think you can use a 4 barrel carb on a two barrel intake if you use a adapter. I hear people don't care for the adapters though, more gaskets to seal.

 

[Tison78_CJ5]

I have been considering installing the high rise I have on it. That way I could put a 4 barrel on it. That would cure that problem. But I need to run down to my friends shop, and measure the height. I will not cut a hole in the original hood. So if it is too tall, I have to buy another hood to cut.
My problem does seem to be getting better. I am starting to think maybe I just got some bad gas. That would be about my luck.

Thanks

 

[PoliceMonkey161]

Hey Tyson,

Not sure how much of a high rise your going with, but keep in mind that the longer intake runners you have, the less off idle drivability you will have. As a general rule tunnel ramming is a trade off of low end for mid- high end torque and RPM's. your fuel charge signal will distort at low RPM's and higher vacuum pressure, but will start to even out and respond better on the upper end of the range for a number of various reasons. You can make it work but it will require some changing of jets and trial and error.

 

[Tison78_CJ5]

Well I just ordered a Holley Avenger, 670 CFM, 4 barrel carb.
My new 304 should be ready in a week.

 

[superj]

Well I just ordered a Holley Avenger, 670 CFM, 4 barrel carb.
My new 304 should be ready in a week.

a 670 is way to big for a 304. you should be looking for something around 400-500cfm for a 304.

chevy 350 v8s came with a 4xxcfm (i don;t remember the size) and i have a stock 302 carb 4 barrel holley on my I6. the holley is a 450cfm.

 

[Tison78_CJ5]

My neighbor told me what I needed. He builds race car engines. He is boring it out 30 over ,going to balance it, edelbrock intake. He sounds pretty confident about it.
I have been told the jets can be changed out if need.
But I am assured it is a good size for it.
Heck, back in the 70s my brother put a 1200 cfm quadrojet on his 351 boss mustang. of course when you pressed the gas, it flooded out.

 

[superj]

My neighbor told me what I needed. He builds race car engines. He is boring it out 30 over ,going to balance it, edelbrock intake. He sounds pretty confident about it.
I have been told the jets can be changed out if need.
But I am assured it is a good size for it.
Heck, back in the 70s my brother put a 1200 cfm quadrojet on his 351 boss mustang. of course when you pressed the gas, it flooded out.

the size depends on the volumetric efficiency of the engine, and the jeep engines aren;t that great.

check out this link: Carburetor Size Calculator | GTSparkplugs

i tried some different rpms and efficiency numbers to see the largest cfm carb i could get onto your stock engine and i could only get about 350cfm. .030 over will not improve volumetric efficiency and neither will the intake swap as volumetric efficiency depends on on the whole intake/exhaust/timing set up to get the best number possible. .03 over will up your displacement to a 313.12 instead of a 304. even using that number, i could only come up with a 360cfm carb.

670cfm is a very large carb. he builds race engines which operate in high rpms all the time. your jeep will not be running up around 5k+ rpms so a 670cfm will make you run rich all the time and give you horrible gas mileage (comparatively speaking) i would look for a 4xxcfm carb and adjust the jets from there.

like i have that 450cfm on mine. its actually too big but i messed with the jets to get it to run right. my engine is a 275 stroker (4.5l) and not that far away from yours. i have an aftermarket intake, exhaust system, carb, upgrade on the distributor and wires and still could easily live with a 390cfm carb.

 

[superj]

i am just trying to keep you from being frustrated and wasting money. i had to learn the hard way on this stuff. i had to learn the hard way even though i went to college for aviation and one of the classes is fuel metering and only about carburetors and how they work. one class was totally on reciprocating engines and volumetric efficiency. i still had to buy to large a carb and learn it first hand though

 

[Tison78_CJ5]

I talked to my neighbor yesterday. He stands by his size to get. We'll know in about a week.
I'll definitely let you know, how it turns out.
I found out both of my 304s have never been rebuilt, and both are 1978. That was great.
He will send all the stuff out in a few days for balancing.

 

[carnuck]

AMC SP2P intake was built for the 304 with economy in mind.

 

[Tison78_CJ5]

Now that's a carburetor...ar, ar, ar.

 

[greg92jeepxj]

That is one pretty carb ! I'd almost marry it if it were legal ! Just kiddin' , I'm not that far gone .
It looks like the venturi's are removeable as some Holley carbs are manufactured to do , if so , you can tune to your hearts delight and hoping as SUPERJ said , achieve the correct volumetric efficiency . Really hoping this works out for you , was worried that this much cfm is overcharging the engine too. Really curious about your neighbors recommendation , but I would never question a pro engine builder since they're usually up on their engine math. But at the same time , I wouldn't argue with SUPERJ about smaller cfm. The 2bbl that a 304 and even a 360 comes with is about 450 or so cfm . The only way I know that an engine can get away with more carb is more cam overlap or lobe separation angle to achieve longer intake open for more mixture .
Now I'm thinking your building a secret weapon of a 304 ! This party is just gettin' started !
Ye haw ! Cam shaft dynamics waking up,an old 304 ! Am I right ? Can I get a witness ?

 

[Tison78_CJ5]

Amen, He has already picked up the cam. He said he doesn't think it will lope too much at slow speed.
He is pretty well known in my location, for his engines, and shine...
That is one pretty carb. The Edelbrock intake looks nice too.

 

[greg92jeepxj]

I've a feeling this jeep is going to spit dirt , take names and terrorize shoppers at the local mall. Just kidding about terrorizing but it will get much attention when you turn the key.

 

[superj]

Hopefully, the cam helps out. It will definitely sound badass and hopefully be more then you are hoping for.

I would love a jeep with a lumpy cam. Just to see people's faces

 

[eric m]

Hopefully, the cam helps out. It will definitely sound badass and hopefully be more then you are hoping for.

I would love a jeep with a lumpy cam. Justin to see people's faces

It's fun, (my dad's cj5 with a 304 has an unknown cam in it, I would describe it as big by stupid) we we're setting at a red light and there was a kid across the street in a stroller who actually covered his ears. Everywhere he goes he has people coming up to him and wanting to know what it has in it.