Re: first build
I can't tell from your photos but do you have adjustment in your drop-outs to tighten the pedal chain? Does the bike have a derailer? If it is a single speed bike there should be a way to adjust the pedal chain tension. I see you're using a tensioner on the engine side so you have adjustment there.
Nice build, by the way. Congratulations.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"