225 Slant needs a good idle. what rpms are you spinning?

500-700 idle ? Shoot I can't keep mine idle under 1000. Are you all setting your timing at that low of rpm ? Geez . Wonder why i can't keep mine at idle at less than 1000-1200 ish best .

May have a vaccum leak. What's your vacuum like at idle in Park?

My Slant has always idled about 750 in park and 550ish in gear. The only time it's ever idled in your range is when I've had a vacuum leak.