What is CFM of Carter YFA?



I'm new to the board, so I apologize if this was recently asked (although a site search did not reveal it).
On Mustang Geezer's excellent site, he has the CFM of a Carter RBS listed as 215.
He mentions YFA's but gives no CFM rating.
The YFA I plan to install on my '81 200 is from the 300 in an '80 F-150.
My present carb is a Holley Model# 1946 1 bbl (195 CFM as per the Holley Tech Line).
Both the Holley and the YFA have the 1.75" carb bore, and the YFA is a true bolt on, requiring only minor modification to the auto trans kickdown lever.
What is the CFM of the Carter YFA??
Thanks for your help w/ this!
:smash: :wrench:
Howdy Rocko:

And welcome to the Forum!

I can't say that I've ever seen cfm specs on the 300 Carter YF. Off the top of my head, I'd guess that it would be similiar to the the RBS. Criteria for comparison is the diameter of the air horn, venturi and throttle bore. Choke parafinalia in the air horn usually changes actual CFM rating from manufactures specs.

Also know the the internal idle circuitry range is preset for an engine with cylinder of 50 cubic inches of individual cylinder vacuum draw. You're putting it on an engine with 33.33 cubic inches of individual cylinder vacuum draw. It is extremely unlikely that you will get the same quality of idle as it does in a 300. The lessened vacuum draw reduces signal through the venturi and booster.

IIRC, Mustang Geezer had to make some internal modifications to get the 300 Carter YF to work well on a 200. Check with him for details.

I'm curious why you choose the Carter YF from a 300 over an RBS from a 250? Please share your thoughts. Thanks in advance.

Adios, David
hi Rocko...Glad to see you finally made it over here!! ;)

This is what I have so far,

1.) 170 ci carb was rated at 150 CFM's.
2.) 200 ci carb was rated at 187 CFM's.
3.) 250 ci carb was rated at 193 CFM's (1975-1979).
4.) 300 ci carb was rated at 220 CFM's.

These were all Carter Yf/YFA carbs.

The reason why the 250 was different was that they used the Carter RBS from 1970-1974 IIRC.

They all switched back to a Holley in the early 80's...Not sure what year right off the top of my head.

I have to work on a carb page too, but thats down the road a little ways :LOL: :LOL:

I always wondered what the Holley 1946 was cfm wise...Now I know its 195 cfm's...Cool!!


Much appreciate the detailed CFM info! Ford switched to Holley 1946's in 1978, according to my Chilton Manual.
What mods did you make to your "300" YFA to use it on your 200?

Yes, one of the reasons I haven't installed the "300" YFA is because of my concerns regarding both Tip-in and initial acceleration characteristics.
I noticed some softness in both areas (compared to the present Holley 1946) after I bolted the YFA on and took a test drive.
Please note that at the time of this test the exhaust was Stock, and the YFA had not been rebuilt, adjusted or tuned. Mid and Upper RPM performance was strong, Low RPM performance was softer (Tip-In response was mushy, but no stumble), Idle was fine.
Question- Since the initial test installation, the exhaust is now low-restriction (I.E. gutted cat, Walker Dyno-Max muff). I have also installed an enhanced "ram air"-type induction. Timing is at 13B, w/ ported Vac running direct to Dist (instead of manifold vac thru emiss controls).
Do you think these breathing and Timing mods would help to compensate for the vacuum signal differences you reffered to and would they improve the Tip-In and initial acceleration performance of the "300" YFA carb?

If not, what mods would?

Also, are there any OEM rocker arms from ANY engine I could install that would change the rocker ratio? I ask about OEM because after-market rockers I have seen require mods to the oiling system.

You asked why I chose the "300" YFA over the "250" carb..
Basically, I couldn't find any 250-equipped cars or trucks at the salvage yard, LOL.
:smash: :wrench:

I had to drill a 1/16 (mighta been a 1/32) inch hole in the throttle plate so that the idle mixture adjustment screw would work and I also had to "shim' the accelerator pump rod so that it gave a longer squirt to get rid of a low end bog it had.

The shim was just a small washer but you would have to have the top of the carb tore off so I could explain how I did it.



Thanks for the info guys.

Rocko- all of the mods/improvements you've made will help with the idle and off idle transitions. I'm with you on the WIG (What I've Got) or the WICF (What I Can Find) 300 YFA carb.

How many turns out on the low speed idle screw are required to draw the highest vacuum reading? My guess would be that it's less than 1 1/2. That would be an indication of a too rich idle circuitry.

It sounds like you're in the right ball park.

Dougs modification of drilling a hole in the throttle plate to lean out the idle circuitry is a good one. It's a Hot Rodder's way of playing with the air bleed circuitry that is built into the system.

Doug- where did you fing the CFM ratings on the Carters? I've hunted high and low, with no luck finding. I'd love to know your source. In fact, I've been able to find very little on the Carter one barrels. Most of tuning and mods I've tried has been extrapolated from Carter and Edelbrock 4 barrel stuff. As you may have guessed, I'm not as comfortable with the YF and YFA carbs and the Holley #1946 as I am the Autolites and early Holleys, but I need to know more. For example, what's the difference between the YFs and the YFAs?

Adios, David

All that info was in all the boxes of manuals and Ford literature that I bought when I "bought out" all the service and parts manuals/literature/training books they were getting rid of from work.

If you stacked the stuff on end it would be about 16 feet high...no kidding!! ;) :LOL: :LOL:

Thats where I've been getting all the stuff for my Ford decoder page and a lot of the stuff for some of my other pages.

It's a lot of fun going through all the stuff and picking out bits of info here and there.

I have tons of info and diagrams from the early/mid 50's all the way up into the late 80's. Everything from tranny & carb diagrams to engine part numbers to sheetmetal, rearend and anything else you can think of.