1st Start stock 340 w/ New or Rebuilt Carb?

X2. Just went through this on a dyno session. Like said above, you really want a known good carb. Break in is basically just a steady-state condition that beds everything in together. It’s important to get the engine started right away and get it up to operating temp before you do any tuning. If you’re futzing around trying to get the thing started you increase the chances of wiping out the cam if it’s a flat tappet.

On the dyno session I mentioned above, we used the operator’s dyno mule carb. It wasn’t the best match for our combo but it started up on the second try and ran fine @ 2,000 rpm. The rebuilt carb we brought with us to try was leaking like crazy and would barely run so it was the right choice not to use it on first startup.