Can't get 1980 Harley Sportster to idle. New

My guess woud be that you either have not got the timing set correctly or something to do with the intake/ carb.

Since you say you replaced the advance weights, this tells me that you removed the breaker plate. I hope that you replaced the entire mechanical advance unit unstead of just the weights. The problem is that the pivot pin wears and replacing the weights does not replace these pins. I always use the needle bearing equipped units.

Now, to check the timing, connect a timing light to the front cylinder and start the engine. Remove the timing plug from the left side of the engine and shine the light in the hole. Bring the engine up to about 2500 RPM. You should see a "dot" in the middle of the hole. If not, you'll have to move the breaker plate to change the timing.

Intake and carb. I've seen brand new intake clamps with new "rubber bands" leak. I always pressure test them. To do this, you must make a plate that replaces the carb and bolts on to the intake. In the middle of this plate, there should be a hose nipple. Rotate the engine until both intake valves are closed and apply about 5 PSI pressure to the intake. Spray soapy water on the intake and clamps to find the leaks. Once the leaks have been stopped, work on the carb.

If you're using the original Keihen carb, you'll probably find that the slow speed jet or the idle port is plugged up. I'd disassemble the carb and soak it in carb cleaner. Make sure all the air and fuel passageways are clear. If the idle mixture adjusting screw is frozen up, trash the carb and get another one.

Good Luck
Steve