Just replaced my lifters and added some new msd wires. Set up initial timing at 8 degrees. When I connected the vacuum advance the timing advanced of course. With or without that hooked up I have a really bad engine stumble when I hit the throttle coming off idle. Makes city driving nearly impossible with the big surge. I calibrated the carb to max rich and that helped but it is still stumbles pretty bad. I am thinking that the carb itself might just be too small for this motor. I have a 454 with a 600 cfm carb. I had it running fairly well before the new lifters and wires but now it straight sucks. My thinking is that with these new parts I either got it mechanically sound and am finding out that the carb is too small, or I have a massive air leak somewhere in the manifold gaskets. I am thinking more towards the too small carb as I seem to have a ton of vacuum but I am not sure. its an Edelbrock 1406 carb, comp 4x4 cam. Initial timing 8 degrees, with vacuum hooked up at idle it jumps to 20.