The carb is a Holley 0-1850SA manual choke. It has 65 jets on the primary and the plate rating on the secondary I am not sure . The 289 has 194/150 stainless valves, Comp cams 270 hyd roller cam, Probe pistons beehive springs , 9.5-1 comp, MSD ready to run. Just wanted to try it out again and thought that the jetting could go down a bit. Seems that the pipes are black and sooty even with the Street Avenger that has 58 in the primary.
The ONE good thing about a Holley is that they can be tailored to work on about anything. So much of it can be modified in one way or another. From jets to idle feed restrictions to power valve channel restrictions-it can all be modded to work for almost any given application.
That said, there are many ways to tune. Dyno. Drag strip. Or my choice-a wideband O2 meter. With a properly working wideband, you can tune idle, part throttle, wide open, everything. Same thing can be done with a dyno session but it's time consuming. But then again so is DIY with a wideband. Every engine I've run an 0-1850 on has needed to be leaned out a good bit. On an old GM 350, I went from 64's down to 54's and it was still too fat at wide open. 54's were all I could find locally. Sold that old pile of feces with the carb on it.
Going to a smaller carb isn't going to help. Sometimes it can make it worse. If you're having to jet it leaner now, chances are good that the boosters are getting a good signal and really putting a "pull" on the jet, which is good thing (most times). I'd try to work with what you have until you can't work with it anymore. They're VERY flexible. I always said that if somebody can't get a holley to work on their engine (and it's not grossly over or under carbed), they need to switch to injection.
Keep messing with it. And do some reading. And don't be afraid to experiment with things. Oh and one last piece of advice....90% of carb questions that are answered on forums are answered by those who know how to make one run....but do they know how to get it dead on??
5 jet sizes from whatever the thing had out of the box. Your intake, cam, exhaust(or lack of), top end rpm can affect jet requirements quite a bit. The model of carb and what it was initially configured affects this as well. You can find the same model carb with 5 list numbers with different out of the box jets.
I have the Street Avenger 570 working well. I have this new 600 sitting around and I am just one of those guys that like to see if it will work. The 1850 was the carb of choice back in the 80's and I had one on another 289 by just bolting it on and it worked great. Maybe the same. Back then it was leaded gas too. Nice smell if it was too rich. I will try the jetting down and if there is no bucking at high rpm it might be Ok.
The original question doesn't make sense. A too big carb (more cfm) means more air and will run more lean, not rich as in the description of the problem. The 600 should be fine on a 289, check the power valve and metering block holes, air bleeds, etc.
A bigger carb, on it's own, will not put more air into an engine. An engine won't take in any more air than it can exhaust. A too big carb could be a little lazy at low RPM's because venturi velocities will be lower, which will not atomize the fuel as well. I suppose this could lead to the condition bmcd mentions as poorly atomized fuel could have more drop out, leading to raw collecting in the intake runners and a leaner intake charge. Raw fuel in the intake could result in soot, no? Like the others have said, I wouldn't think the 600 would be too big for the engine to run properly, so there might be something else causing the problem.
I have a 600 cfm 1850 that I've run on a few engines. This carb has been overwhelmingly rich on every engine it's been on (2 ford 302's and a buddy's chevy 350).
I always start at factory jetting (66 primary, and I think the plate in the back equates to 74) and then work my way up/down as the engine demands. I jetted down until I was at 56, and decided to try a smaller carb. Remember that one or two jet sizes either way is no indication that the carb is not sized correctly. Holley generally jets a little on the rich side to avoid a lean condition, and other factors like altitude can easily make 1 or 2 jet sizes different OK.
Is the 600 CFM too big? Maybe a little, but with vacuum secondaries its not a problem. It seems to me that it needs a lot of mods to work WELL on anything I've tried it on. With a wideband 02 and changes to the air bleeds, PVRCs, IFRs, etc, I suspect it would do very well.
Ran a 600 years back and had no issue on it . It was on you basic 289 cast iron intake with 225hp. Bolted on and never had an issue. Now it seems I have this bigger Comp 270 hr camshaft and it tends to have sooty tail pipes and the ridge on the spark plug is blackened . Mine have 65 primary , not sure what the secondary plate is . The duration of the camshaft may cause an incomplete burn..?