Carburetor CFM and Carburetor Selection

Stock FSJ Tech Area

sierrablue
Posts: 1208
Joined: Wed Nov 30, 2022 8:02 pm
Location: MN/CO

Re: Carburetor CFM and Carburetor Selection

Post by sierrablue »

weeegoneeer wrote: Sun May 14, 2023 4:31 pm I have a street avenger 670 and it is way too big, can confirm what was said earlier - I run a AFR gauge and it's all over the map (though runs OK). Also ran a 470 TA for a bit and it was no bueno for street use. Holley was actually awesome here, they swapped out my TA for the SA for free.

Eventually I'll probably move to a 450 CFM or so 4 barrel with small primary venturis, see what that does. Really want to steer clear of TBI but may get there if a small street carb doesn't work.
If you're running into issues with it being too much, you might try something with vacuum secondaries. Then even if you feed it more throttle than it can deal with, the secondaries don't allow you to flood it out/etc. Also metering rods help with that.
'71 Wagoneer (DD)
-B350 (HEI, iron 4-barrel, Edelbrock 1406), TH400, D20
-'74 D44 front (nonpower discs)
-custom headliner
-Front shoulder belts (rears eventually)

viewtopic.php?t=23070

There are 2 major differences between new Wranglers and FSJs. FSJs are meant to be both utilitarian and capable, not just capable. FSJs are also rarely initially recognized as Jeeps by the average American.

weeegoneeer
Posts: 230
Joined: Wed Apr 26, 2017 10:34 am

Re: Carburetor CFM and Carburetor Selection

Post by weeegoneeer »

SA 670 does have vacuum secondaries. It's not so much about flooding out, when I dig in it's dialed - drops to 12.5-13.5. At 2750-3100 RPM (the highest this truck will ever see), it's wicked responsive and MOVES.

It's more about control right after tip-in and not much air is moving - runs leaner than it should for a second. And yes, I've been through all manner of pump cams, squirter nozzles, etc and am at the best state possible for what I got right now. My gut says if more air volume was moving off idle through the venturis the problem would go away.

I might try a spread-bore with vacuum secondaries and a funky adapter plate for the performer intake.

To the original poster though, you're right to consider your max requirements IMO. An 800 CFM carb isn't going to give you more power - and smart to consider your application (will you ever see 5500 RPM? Probably not - you're going to live in 650—3000 land most of the time). If you're offroading - the Holley TA might be the move (but not if you're mainly on the street). If you're going around town mostly, 2-barrel or small 4 barrel is probably the move. Not claiming to be an expert and want to be schooled, but also just relating what I've noticed.
1984 GW

sierrablue
Posts: 1208
Joined: Wed Nov 30, 2022 8:02 pm
Location: MN/CO

Re: Carburetor CFM and Carburetor Selection

Post by sierrablue »

Ohhhhh that stupid stumble. Mine does that too when it's cold, and you can tell that it kind of does it warm, but it doesn't cause any major issues when it's warm. You can just feel that all of a sudden it has a little more power. Mine got a lot better when I got the right metering rod springs on it. My dad's '69 Cougar does that too; 2-barrel Autolite, and it's a huge inconvenience on that one. I've found that more timing helps on mine 🤷‍♂️

@Scotty, I would say that you're not going to have an issue if you go with 500 or 600 cfm, or even more, as long as you have the vacuum secondaries. And that way if you decide to give it some headers or something and it pulls a little more, you don't have to put a totally new carb on because now it flows more.
'71 Wagoneer (DD)
-B350 (HEI, iron 4-barrel, Edelbrock 1406), TH400, D20
-'74 D44 front (nonpower discs)
-custom headliner
-Front shoulder belts (rears eventually)

viewtopic.php?t=23070

There are 2 major differences between new Wranglers and FSJs. FSJs are meant to be both utilitarian and capable, not just capable. FSJs are also rarely initially recognized as Jeeps by the average American.

akguy09
Posts: 301
Joined: Mon Aug 30, 2021 6:11 am
Location: Ellicott, Colorado

Re: Carburetor CFM and Carburetor Selection

Post by akguy09 »

weeegoneeer wrote: Sun May 14, 2023 5:02 pm SA 670 does have vacuum secondaries. It's not so much about flooding out, when I dig in it's dialed - drops to 12.5-13.5. At 2750-3100 RPM (the highest this truck will ever see), it's wicked responsive and MOVES.
drops to 12.5-13.5.....its not lean 12.5 is a good number unless you are referring to vacuum, if referring to AFR then 12.5 is fine
1979 Jeep J-10 304/T-18
2017 Jeep JK 2DR
2021 PowerWagon
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