I've very new to motorized bikes. I have a kit I was going to install, but a pre-built bike fell into my lap. It's been running intermittently. Sometimes good, sometimes bad. So I looked at the cylinder head and there was a slight leak. I tightened up the head a bit, but it doesn't seem to be sitting strait against the top of the cylinder. I'm afraid of over tightening. It also seems as if the head isn't sitting flush. maybe it's warmed. That said, the engine hasn't even been run for a single tank. Its still in break in. Not sure what I need to do, or exactly which make of engine this is. It's different then the one I have boxed up.