Motorcycle Repair: Backfire / Low Power, air screw, drag pipes

Question
QUESTION: Hello Mike,  I just bought a 1991 FLSTN last night.  3500 mi on Factory Reman Engine(stock V2).  Screaming Eagle intake and Drag Pipes.  Problems:  1)Poor starting cold(reqires a lot of choke)Choke will not hold open, slides back mostly closed.  Also Engine Pops and backfires till fully warmed up.  hen it still acts doggy.  2)When crusing the bike has poor pickup, also pops and backfires under load.  When I turn the console switch to "Lights"(from the ignition mode) the bike Backfires loud! Additionally, lights are ON when the switch is in the Ignition mode. Bike turns over good(as I was Thinking weak Battery).  Could It be the Ignition coils or corroded battery wires?  Also the rear brake dosent do anything when applied.  Is the Master Cyclinder under the chrome rectangle, just ahead of the footbrake lever?  I'm going to change plugs today, Clean the carb, adjust the idle air screw, add a little marvel oil to the fuel and try to fill and bleed the back brake system.  Any thoughts to the low power and wierd popping/ backfiring  would be appreciated.  Thanks in advance Mike.

 Max

ANSWER: Pull your spark plugs and let me know what color they are. Are you running a stock carb? Dont add the marvel oil, it wont do anything.
Lights are suppose to be on in the ignition mode, they are built that way.
the master cylinder is located where you think it is.
Mike

---------- FOLLOW-UP ----------

QUESTION: Hi Mike,  Plugs are light grey(lean looking).  Bought the bike from Denver Area, 5500 feet elev.  Replaced the plugs, cleaned and re-oiled the K&N, set the idle air(wanted to run best almost screwed all the way in).  Im about 1/2 turn off the seat.  Stock CV 40 carb.  Runs much better now.  added synthetic fluid to the brake resivor and bled it, although I feel it still has some air, after I let it sit the pedal goes down farther the first stroke, then nice and hard after.  Backfiring has quit, bike has to be warm to idle good.  Any way to tighten the choke so it will stay open?  By the way the bike will start cold without choke now.  I just pump the throttle 2 times and it will fire.
 
 Thanks again Mike!

Answer
Your air/fuel mixture screw is closed to much. Should be around 1 1/2 turns. Change your intermediate jet to one bigger and test ride. The other time you can do is get a Dyna-jet kit for your bike. In it you will find the jets you need and how to set the carb. The kit will give you better throttle responce and a smoother running bike.

It sounds like you still have air in the brake system, so keep bleeding it.
To get the choke to stay open look behind the knob. You will see a round plastic nut. Slightly tighten it. Dont try to tighten it to much or you will break it.
Good luck and happy riding
Mike