I double checked mechanical timing, reset distributor etc and it still acted the same. I took off aisin carb and installed algas carb with a impco regulator and after cranking for 10 seconds, engine started with a lot of steam coming out of muffler. I ran engine for 20 minutes until little steam was coming out. Reinstall aisin carb and regulator and now it runs fine. As I mentioned in first post, job came in for head gasket so o guess it partially filled muffler with water. I've never seen this problem before but hope this helps someone else in the future. Thanks for reply Kevin.