I've been trying to smooth out my 8ba flatty. It has a constant rough idle which sounds to me like it's missing but not a definite skip. Plugs all look fine & even. Used a neon spark test light and all cylinders seem to fire evenly. Ignition is a Mallory Unilite with MSD Blaster coil. I'm using a ballast resistor. Carbs are 2 94's on a standard Edelbrock 2x2 manifold. Cam is an Isky Max-1, but I don't think the roughness is from the cam. Vacuum pulls a fairly steady 18" with a slight fluctuation. Engine is freshly rebuilt. Maybe unrelated, but what seems strange to me is carb idle mixture screws are almost closed for highest RPM setting. Carbs were bought rebuilt on internet. Car otherwise runs good - No pops - No floods - No stalls. I need some opinions of where to go from here.
I would guess your carbs are the problem. Could be the power valve in one or both and you will probably want to take them apart and test that first. The "chinese" power valves (or wherever they are made) are known to fail or not work properly. There are several guys on HAMB and fordbarn that sell good ones. If not the PV's then it might be the carbs are not properly tuned for your setup.
Take the air cleaners off and look down the carbs to see if any fuel is flowing out the booster venturis. There should be none at idle.
It sounds like you have addressed the necessary issues. The power valve and float problems are the common ones. Have you synchronized the carbs? I purcashed a synchronizer from speedway and set my carbs up. My issues were more towards idle problems. I had no misses unless the idle air was leaned out to much. I had the best luck shutting down the idle speed and air adjustments on one carb and use the other for the idle circuit. Good luck it can be a hair puller.
These carbs were acquired thru ebay and were supposedly rebuilt by knowledgeable experienced "94" guy. Maybe you can never be too sure about things.
They might be rebuilt right and the experienced 94 guy might be good at it but if the PV's fail or if the carbs aren't tuned it won't run right. I would test them first to see if they are working right. If I remember right you remove them and suck on it to see if it holds vacuum. Somebody might correct me if I am wrong. Check with Uncle Max or Ken.ct on fordbarn, these guys know their business and are old holley/stromberg carb experts. At any rate your problem sounds pretty minor, nothing serious I don't think.
Try adjusting the carbs with the filters off first. I had a supposedly good set of filters that were too restrictive causing the exact same adjustment problem you describe. Next... burp the carb.. open the adjustment screws all the way or preferably totally out if possible. Bring the engine up to 3000 rpm and put your hand over the mouth of the carb. Your rough idle may be due to the fact your carbs are not in sync causing a lean mixture at some of the cylinders. Pull off one plug wire at a time while at idle. You should be able to hear a variance in engine sound on each cylinder wire removal. I spent a week trying to find this type of issue. You could also reinstall a single intake and run each carb on the engine at a time.
Looks like I have to do a carb teardown and double check those PVs. I should probably have a couple of new ones on hand first. Any recommendation as to whom to buy the right ones from? Also why should my idle mixture adjustment screws all be practically closed for best running?
The Jalopy Journal
