I just want to make sure my logic is sound here and I don't waste my time doing something that won't solve my problem. I have a mostly stock 454 (stock internals, long tube headers, carb spacer) and I have an AFR gauge hooked up. I've been trying to dial in my carb and it's consistently inconsistent. I'll set my idle mixture screws and the carb will sometimes be rich, and sometimes be lean.
I've got it leaned out in the idle mixture to try and prevent dieseling at shutdown but it will still read like 13.4-13.8 afr with the screws 1.5-2 turns out. Often, it will "jump" a little where the vacuum drops 0.5-1 inHg and the afr jumps 0.5-1, but it isn't consistent like a misfire or anything and I haven't found a vacuum leak to date. I've also pulled the valve covers with the engine running and verified I don't have a dead lifter or cam lobe or anything. I've had my timing dialed in for a while on a brand new MSD distributor so I don't think it's a timing issue either.
It also loads up when I brake (afr drops to 11.5-12.5) and that will temporarily screw up the idle mixture (makes it run richer for about 10-30 sec before it levels back out to ~14.5).
I'm thinking I've either got junk stuck somewhere in my carb, or my float is set too high and it's letting little bits of extra gas into the manifold. I have a rebuild kit on the way and I'm going to redneck hot tank my carb before I rebuild it to make sure any foreign debris gets cleaned out of all of the passages. Can anyone provide any insight?
