Start with timing. You need to correct that first. Do not lock it out, or get it “all in” by some arbitrary RPM. The engine WANTS a curve.

You may end up using manifold vacuum to clean it up. I don’t read Vizard nor do I care but if you do do MVA you need to understand what happens to the curve when manifold vacuum goes away.

If I have to run more than 24ish initial then I know the engine is built wrong, or the engine is something like you have. An engine you want to make better. This is a sure sign the compression is down, which you already know. It is what it is.

The other issue is if you Jack a bunch of initial timing into it then add MVA on top of that you can and probably will run into tip in detonation. You have to balance your initial with MVA, plus you need to see how much MV you have at idle and get the vacuum can that can pull some timing with that low MV.

If it was me, I would set the initial at 24 and start there. See if you can get it close without MVA. I say 24-25 initial because if you get much over that you will absolutely KILL the middle of your power curve because these engines do not want max timing at peak torque. In fact, you’d be shocked what these engines want for timing at peak torque. It’s usually in the low to mid 20’s. So think that through.

Let’s just say your engine wants 26 degrees at peak torque (and I’m going to assume your engine has a peak RPM of about 5500 and peak torque is 1500 RPM below that…which is my best guess for now) and you start out with 28 initial. You may be ok IF you can hold that 28 degrees if timing all the way to peak torque and then have it gain 1.5-2.0 degrees per 1000 RPM. But that is damned hard to do unless you modify the advance weights (you have to make them very light to delay the start of advance) and even if you lighten the weights you may not be able to get a heavy enough spring. I know unless you wind your own springs you generally have to make your own.

At that point if you need more initial than 28 at the MOST, then you need to reduce the initial and add MVA and figure out what can you need or can modify to get the timing you want.

Once you get that sorted out, you can get into the carb. First mod is to lower the Idle Feed Restrictions to the lower position and see how much that cleans up the idle, if any. If it is still on the fat side you have some options. You can reduce the IFR. Or you can reduce the Main Air Bleed. Or a bit of both.

Once you sort all that out, you can start tuning the primary side of the carb, including the power valve.

The correct way to fix this is not easy or cheap but the end result is worth it. Sadly, many just lock the timing out and send it. Certainly is faster, easier and cheaper. But it’s not better.