Just had 69' 400cu rebuilt by local reputable shop. Running it for the third time just at idle in the garage as I re-Assemble, I've noticed the pass exhaust blows clear and Hot but the driver side is blowing much cooler and frequent steam vapor. Wondering if it is possible heat riser on new manifold or something worse. Manifolds are brand new. Any ideas or advice before I call builder up. Was told no cracks in head.

 

Condensation is normal right after startup, the heat riser takes a few minutes to warm and open 100%. Does it disappear over time?