So I was playing around with this engine I got it started and it runs great but just a little curious what the port on the bottom of the crankcase is for. I had it running for about 20 minutes it had good transition off idle but never sounded like it was reaching high rpm's , and acts like its backfiring at full throttle. I ordered a tach and I'm gonna pull the carb off and give it a good cleaning and try to tune it again.