I have a 1977 sportster. It was my dads, and I don't know a whole lot about it. Its been sitting for about 6 years and I wanted to get it going again. I got a battery and was able to get it starting. It didn't run right so I thought id clean the carb. I went out and bought a kit and replaced all the rubber pieces and I cleaned it. To take the carb off I had to take off the intake, because the coil blocks the upper nut. I put everything back on. When I started it, it sounded like it was full throttle so I turned it off. I started it again and it happened again. I don't know if I messed something up while rebuilding the carb? Or maybe the throttle cable? Or a leak in the intake? I have no idea.

 

It wouldn't surprise me if you had an intake leak, although I think by '77 they had the rubber band type seals and not the o-rings; the bands are a little more forgiving. Take the air cleaner off and ch3ck the cable adjustment first, make sure the butterfly throttle valve (I'm assuming stock carb? Or maybe S&S Super B or E?) snaps closed when you twist the throttle and then let it go. You may have a 2 cable system. In this case, one pulls the throttle open; the other pulls it closed. It should still snap closed on its own. Having one or hoth cables too tight can cause a problem, as can a worn out cable.