Here's my method.
- With a 500 watt pan heater, I bring the oil up to 140-150°F before priming the system. Not only does this make the oil flow and prime much easier, it gives a little heat to help with ZDDP activation at first startup. Before I got the pan heater, I had a dedicated pot on a turkey fryer to bring the oil temp up before pouring it in. This isn't a necessary step, but I figure it can't hurt.
- I triple check everything before trying to start it for the first time. You can mess up and glaze a good hone job cranking the engine over and over and over trying to figure out why it's flooding or not getting spark.
- On first startup, I let it idle maybe 10 seconds. Longer than that, you risk glazing the hone with insufficient piston speed. Just long enough to see a readout on the AFR gauge that's decent enough (not shooting for target at this point) and for oil pressure to come up and stabilize, and then it's straight to 2500 rpm for about 30 minutes. This gets the oil hot quickly which is essential to ZDDP tribofilm formation. It also ensures good oil splash around the valvetrain. You want the engine to get good and hot for this period. I target 200-220°F coolant temp and 240-260°F oil temp. Also, with a carburetor, I do this all with the idle circuit, adjusting the speed screw and mixture screws. Thus, removing the throttle, main jetting, bleeds, etc... from the equation. With a locked distributor, I keep the spark timing very late at just 6-8° to help it warm up faster. Once the oil and coolant approach 200°F, I gradually advance the spark (and adjust idle circuitry accordingly) to about 25° to stabilize things.
- After 30 minutes, I shut the engine off and let it cool all the way down to ambient temperature naturally. Again, not totally necessary, but with dissimilar metals with different expansion rates meeting each other for the first time, it makes me feel a little better to heat cycle the engine.
- Then it's time to set the rings. Without a dyno, I do this at the track (or on the road if you live out in the country like I do). I get the carb and distributor tuning close and conservative. I make pass after pass, adjusting the carb and timing if needed, and getting some cycles in. My Camaro has a TH350 with manual valve body so I launched in 2nd gear and short shifted to 3rd as soon as reasonable. I did this to increase load and slow the rate of rpm increase down track so I can monitor air/fuel and oil pressure more accurately. I like to make at least 10 passes, over 2 test nights if I have to.
- After that, the break-in is done. Adjust tuning as needed but you're good to go. I drain the break-in oil, change the filter, and install the oil and filter of choice. Also, for my mild compression (10.5:1) SBC bracket engine, I did all of this on VP C9 fuel which is unleaded ethanol free gas with ~97 octane. (R+M/2) After the break-in, I switched carbs for E85.