Bobster wrote on 12/31/69 at 16:00:03:does that sound like the problem to you Rob?
I was simply replying to your post on not seeing 55 pilot jets. However, after reading the whole thread, it could be a couple of things. Please read the
Mid-Range Power & the White Spacer (Backfire) thread in the Tech Ref forum. The white spacer mod may help with the backfiring too. Since you've stated your exhaust is welded, I'd only suggest that you check/replace the gasket between the header and the engine. That caused me definite problems very similar to your description. My mixture screw only backed out 2 turns and locked up. I replaced the pilot jet with a 55 and that portion of the tuning was fine (I got lucky). It can't hurt for you to try it and it's inexpensive.