Tri powered distributor

Ok got my 78 250 Tri powered running good except seems like after rev's up takes to long for rev's to go back to 600 RPM drops down to around 1100 to 1200 for about a minute or so. Wanted to know if the vacuum advance is causing this. It has the original DSII.
has been bored 30 over has yella aluminum roller rockers Block was milled 50 thousand and head was milled 80 thousands. It says in the offenhauser instructions that i might be better off with a mechanical Distributor any suggestions?

If your DS11 is stock, you might be wise to get one of my DS11's listed in the small six for sale section.
Might be sticking weights in your DS11.
I would have to have more info on your vacuum advance connections.
Could also be binding throttle linkage not returning to your base idle setting. Bill

No throttle linkage is not binding have engine on run stand and can see it is not binding. i beleive it is a DSII already are yours recurved for this application.

The vacuum advance should drop out with the throttle blades closed if you are using ported vacuum like off the center carb. Otherwise it's always in to some degree on manifold vacuum source. Maybe something is binding/sticky in the distributors advance plate.