The baseplates are known to wear. Another issue on the better M4M 800 cfm carbs is the limited idle fuel. My Holley reman, which ran great for years and my 78 403 carb ran awful on my 9.5 to 1 Olds 350 with the small 204/214 cam. Crappy idle, just stumbled and ran shitty. I could have modified the idle tubes but instead I sent it to Everyday Performance about a year or so ago. It was around $250 for a custom tune using my core and no plating but did do the rear bushings, the front were OK. It ran so much better, no more idle screws 5 turns out. The idle was a touch rich, better than ridiculously lean. Since I changed the combo to 9 to 1 with more intake duration, it runs even better. I did make the APT adjustable on this carb, a thread in plug and notched the adjustment for a small flat screwdriver. I believe it is one full turn from where Ken set it, I gained at the track by setting it richer, it kills fuel mileage that is for sure. An easy adjustment, I may set it back again today. Just clean the hell out of it, did you get a new float? Sometimes you can get away with the old one, sometimes not so much.
