Engine starts smooth, within 20 seconds starts cutting out and missing.

The distributors on this engine give a BUNCH of trouble and exhibit those exact same symptoms!! Hard to pinpoint it also as it is a multi componet dist. The only cure is replacement of the distributor assembly with a NEW one! Just something i have run across at the shop. Let us know how you make out with this. Have a mechanic check it out but it most likely will not have a relàted code!

agree with pushrod