I have two sets of carbs to try on this engine. Well, 3 if I want to throw some extra stuff together. For now, I have a set of "550" cfm carbs spec'd for this combo by Allstate. They started with 600 vacuums and converted to mech. secondaries. They installed some of their straight leg skirted annular boosters. They figure the real estate the new boosters takes up makes them closer to 550 cfm.
Anyway, I decided I also wanted to try and make a set of my own. I was thinking of a high flow 650-ish cfm vacuum. So, I started with two new replacement main bodies from Holley. They are 1 1/4", 1 5/16" venturi. I noticed when setting the base gasket on or even the baseplate that the venturi was small up until the last 1/4" before the base. It has two flares at the bottom to go out to the 1 11/16" throttle bore size.
I also wanted to install some different boosters to replace the generic straight legs. So I knocked those out and now I can also deburr and blend the entry into the venturi.
I was very careful to leave the entry size the same. I found a socket that was exactly 1 1/4" and another that was 1 5/16" OD. That was my "gauge". I decide to port them to the full 1 11/16" size to match the baseplate perfectly. I spent a good couple days whittling away. I used a small metal ruler as a straight edge to make sure it was a consistent taper from entry to exit. I used sharpie near the entry, so I knew if the grinder was getting close so I could keep the entry the original size.
I decided on trying some fancy threaded annular down leg boosters.
I got some new replacement HP metering blocks and removed the IFR from the upper location and installed some 6-32 restrictors in the lower position. I also tapped behind the power valve for 4-40 restrictors.
I had my machinist put the main bodies in the Bridgeport to counterbore for the tapered nuts on the threaded boosters. Here is a test fit.
One thing I noticed is after porting, the casting became very thin near the center. I was afraid the gasket would not seal there, so I filled the center with JB weld and trued the surface.
After I re-installed the boosters, I surfaced the other sides to take any warpage out and make sure the nuts and boosters were not proud of the surface. The sides were nicely warped out of the box....
I am using Quick Fuel jet plates on the secondary. I did have to notch the floats and reseal them with epoxy. The floats are nitrophyl.
I installed some billet baseplates and also swapped out the primary shafts for the original Ford style arms.
These are some oddball carbs and didn't know what else to call them.
A couple pics installed and ready to run.
So last night I decided to try them out, but it didn't go so well. It idled very high and was lean and wanted to die after a rev. Now, I just ASSUMED it would want a little bypass, so I drilled the butterflies from the start. WRONG. I had the throttle plates completely closed on both carbs front and back and the mixture screws rich and it still idled at 1500 and was a sack of potatoes. So I figured I better change the throttle plates. This morning I dug out a new set of spare baseplates for a 660 that I could rob the blades from. Swapped them out and fired it back up after lunch. I was happy to see it was running like a top now. Idles well down to around 1200 or so where it's happy and mixture screws are where they should be. Revs nice after swapping in some 35 squirters and comes right back to an idle without stumble or dying like before.
https://m.youtube.com/watch?v=QnAYeEJWYd0&pp=ygUjRm9yZCBmZSAzOTAgb24gaWRsaW5nIG9uIHRlc3Qgc3RhbmQ%3DNow that both sets of carbs are fairly sorted out, I feel ready to drop it back in the car. I think I left out a bunch of details, but that's the gist of it.
