First I want to say that I love my current Autolite 4300 (Ya I know). I have learned the in and outs of my current 4300 with the smaller 431 CFM. From my research my current version is 1967 vintage with a tag #C90F and would not have come on this engine. C90F is stamped on the base plate as well and I have the large adjusting screw on the back.
My 390 tops out at 4500 rpm and I am pleased at the performance. I learned a way to stop any hesitation by altering the accelerator pump check valve breather among with many other things. So I have been thinking of trying to get a proper 4300 to put on the 390. I have lost my carb documentation as to which part number belongs on my 390. I have known the current 4300 doesn’t belong for a few years but have tweaked and enjoying the current set up. Cam is a stock-ish Eddy 2106 and with calipers the bore is .020" over with a C6. So can someone tell me which part number belongs on my 390?
From what I recall from my lost data I should have the larger 1-7/16" primary’s and 1- 11/16" at 650 CFM, I think. C90F-D I think it was. My next question is will it be worth it?
I have also read that the 2100 was used in 1969. I have seen nothing that makes me think it had a 2100 in there, thoughts?
I may make this my winter project and am starting to research again.
Thanks men I’ll be looking out for one. There’s some on e bay. Before I go to far, can I get comments on whether the additional 100 CFM will have much influence on a stock 390 with a C6?
It will be a major improvement. That’s why Ford did it then - the 470 CFM carb like the one you have were just too small for a 390. It’s 130 CFM difference.
Thanks Royce, I believed that would be the case. One appreciates confirmation when they don’t know for sure. My main concern would now be having to add some cash to my rear tire slush fund. My rear tires seem to be wearing more than normal, lol.
A big tourqey street engine topped with a too small mechanical secondary carb ? Y ? Y ? Y ? …unless you are being judged for points get that thing off ! Slap on a Holley Street Warrior low cost 600 cfm vacuum secondary carb…unlike the eddieblock …lol the fuel inlet and the kickdown linkage are where they should be. The engine load will control the secondaries…and a properly adjusted kickdown will be GLORIOUS. Build a lexan display case for the factory carb and put it on display https://youtu.be/as2fXw7Ny0U
The C9ZF-D 4300 carb on my 69 M code XR-7 is a 470 cfm mechanical secondary carb…when it was not able to outrun the H code vert …I thought…this is a freshly restored carb…why cant it outrun the 2 barrel ? Turns out the mechanical secondary lock out lever was blocking the linkage…I have seen several listings identifying it as a mechanical secondary carb…? There is linkage connecting the primaries to the secondaries …?
That’s a common misconception. The throttle valve plates on the secondaries of the Autolite 4300 are mechanical, but the secondary air valve plates above those blades open in response to engine load and available vacuum / RPM.
The mechanical throttle blades allow the carburetor to “see” the vacuum available. The actual metering of the secondary fuel / air mixture is vacuum operated. Not strictly mechanical like a Holley mechanical secondary carburetor.
The Autolite 4300 was not made for very long because it had a lot of problems.
Now see, I learned something. I have read copious articles and manuals on the 4300 and my understanding was vacuum secondaries but I never made the connection of exactly what the mechanical part of the secondary plates were technically doing. RB’s post made that clearer.
When growing up all the bad boys put Holley’s on their cars. I never did but my early “he plays with cars” period in life was shorter than most. I will consider a Holley as I move forward. However, if I can find a good C9ZF-F core without needing a second mortgage, I would like to restore it over the winter and use it. My current 4300 may get sold or traded for funds. I see the tags on fleabay are $50, we will see. I understand both sides and will continue looking.
Part of my angst in this is that my current set up works well. But I can have more, so here we are.
Current combo works well
May I suggest that you cant really say that yet because you have no idea what level of improvement you will see when you make the change…I think it will be HUUUUUGE !
The Holley will truly wake the car up …get the kickdown working properly and you will be AMAZED
Perhaps I should have stated it this way, current combo works well for what it is. When I got the car it didn’t run well and I got to learn a lot by making it run well (with what it had). But as I stated " there is more". And, you are correct, I don’t have any idea what level of improvement I will see. I thought it would be substantial but, that is why I asked, because I have no experience with putting a larger carb on any of my motors. My only experience with big blocks has been in our boats. Currently I have twin 502" beasts in the boat we have now. But, that is another realm in and of itself.
I get it. Come spring there will be a 600 CFM sitting on my intake one way or another.
To sound like the old weird guy who natters on again, you can get good power out of the larger 4300 - as I did in '72-'73 with my 351C Cyclone that ran low 14s with it and was responsive all over the tach.
Yeah, my 1970 600 cfm 4300 with the 351c seems to smoothly deliver plenty of power, but idle is often a bit rough. And it seems really susceptible to sediment plugging its circuits. I hear lots of complaints about the 4300 - what were it’s weaknesses?
Mostly that you couldn’t do anything with it bolted to the manifold. Jets only on the primary side, and even then you had to fight various rods and clips that passed through the top section in order to reach those. Metering rods instead of jets on the secondary side was a real blow.
