2003 sportster poping with lose of power

If the exhaust note sounds like a jet engine ,loud hissing,the catalitic converter has plugged. Makes the symtom you are speaking of.

A 2003 model with only 50 miles?? Wow....well,since youve already taken the carb apart and cleaned it,did you hook up the vaccum line for the VOES switch on the intake manifold? If so,..when you get the bike running,..spray some brake clean around the intake where it bolts to the heads.If the idle picks up,or starts to sputter,..youve got leaking intake gaskets. Which is a good possibility on a bike that old with that few miles on it.The choke essentailly adds more fuel to the motor,and by what your saying,the bike is obviously running lean. Also,...im ASSUMING that you have fresh gas in it,and the petcock is turned on.

you need to adjust the white nob on the carburator

Ok, as a general rule, I only run the enricher for as long as I need until I can keep the engine running with the throttle. If you run the engine too long with the enricher, you'll foul the plugs. The enricher is VERY rich.

Your bike is jetted correctly. There is one other thing you could do and that is to take the slide out of the carb. Then remove the needle. Put a 3mm flat washer on the needle from the bottom (long) side. Put it back together. What you are doing is raising the needle by the thickness of the washer, about 0.020". This will richen up the mid-range mixture just a bit. It seems to help.

Now, you don't want your engine to heat up too quickly. If it does, the mixture is too lean and a lean mixture is fine for a water cooled engine but death on an air cooled engine. I usually run my engine until I feel the rocker boxes getting warm. You also don't want to take off and run your engine hard when it's cold. You stand a good chance of blowing a head gasket. As the engine warms up, the cylinder and the heads "grow" due to the heat building up. When the engine is cold, the cylinder and the heads have the least amount of torque on them making blowing a head gasket or a base gasket more likely if you run the engine hard. Be patient and let your engine warm like it should.

Good Luck
Steve

could be a ignition unit (s)breaking down when it getts hot ?
could be a tank breather not working or a restriction in flow of fuel
could be a valve not opening fully or closing fully ie tight valve

fit in line ignition tester and run unit and see if spark disapears when unit gets hot if so ignition prob if not its other problems

worth a look

cheers

One thing I noticed right away is you say full choke for 6 miles, WOW, that might be your cause, one of the spark plugs is gas-fouled. Change out the plugs, let the bike warm up some before you drive it so you don't have to use the choke/enrichener knob as much as you do. Let me know how that works out. BTW, I warm up my carburated HD until no choke is needed before I ride away, it can and does take some time.

adjust air mixture screw at rear of carb tighten it first then loosen it 1& half turns give it a go

Clean and adjust or replace spark plug first thing.

Most certaintly a fuel problem. It sounds to me like you might have a high speed jet a little stopped up. I would pull the carb and clean the jets. If the fuel is a little old, and I do mean a little, and the bike sat a little bit, the carbs probably a little varnished. The gasoline we have no days aint nowhere near what it use to be. Clean carb and all should be well. Also for future referance if you know your gonna let the fuel sit more than a couple weeks, I would use a fuel stabilizer and run the bike a while to make sure the stablelizer gets in the carb.

It sounds like your carburetor is flooding, check to see if the choke is set too tight.
to do this, when the engine is cold, remove the air cleaner assembly, push the gas pedal one time to the floor. in the carburetor throat is a flap, this flap closes as engine cools so the engine receives more fuel for cold weather starts, the flap is at the top of the carb. this flap should have about a 1/8" gap between the throat wall and the flap when it is fully closed, if if is completly closed it will give the engine to much fuel and cause it to flood. if you need to adjust just follow the linkage that the flap is attached to, and it will lead you to the choke housing, this is where you can adjust it.
once this is done start the engine and let it warm up, as it warms up this choke flap should open completly up in a vertical position.
if it doesnt, then you probably have lost power to the choke housing or your heat tube that comes from the exhaust manifold to the choke housing is bent, off or missing. most likely yours will be electric.
i hope this helps, good luck