Now that you have completed the set up and installation process, you're ready to start it up and take care of it. Remember, if you have set it up properly, the engine should fire as soon as there is fuel to the carburetor. If it is constantly backfiring, stop and recheck your plug wiring and ignition timing.
Once the engine is started, you're almost there. Now hold the throttle above 2,000 rpm until the engine reaches normal operating temperature. Once that is achieved, drop the rpm to idle just long enough to check the timing with a timing light (if necessary, make quick timing adjustments and resume holding the engine at 2,000 rpm for the next 20 minutes). At below 2,000 rpm, the oil pump will not supply enough oil flow for components to properly break in.
During the initial running, check all around the engine for any possible leaks and correct them right away. There may also be some smells and even some smoke during the break-in period, but these are usually the result of oily handprints on the engine and exhaust system and/or the curing of all the newly painted engine parts.
After the engine has cooled somewhat from the break-in procedure but is still warm, change the engine oil and filter. Check again for any signs of leaks and check all fluid levels before driving the vehicle for the first time. Plan on easy driving for some time, (i.e., no towing, steep hills, sustained high-speed runs, or racing around town). After 50-100 miles of easy cruising, find a secluded straight road and accelerate quickly from 30 to 50 mph, then just as quickly, back off the throttle and coast down to 30 again. This puts a load on the piston rings to get them to seat. Repeat the 30-50-30 procedure about a dozen times, and you're done.
Now that you're done breaking in your engine, the rest of your driving can be normal after this (but still without towing or racing). When highway driving, it will help if you don't spend all day driving at one speed, but occasionally vary the speed. After 600 miles, change the oil and filter again. At 1,200 miles, you can consider the engine broken-in and, after another oil and filter change, you are prepared for many years of performance and driving pleasure.