I am trying to adjust my mixture screw due to very low gas mileage, I back the screw till the bike starts no more, and I turn the screw 2 times and adjust inward correct? I do not have a manual yet.

 

No,turn it in (clockwise) tell it bottoms out gently,than turn it out (counter clockwise)
2 1/2 turns and work from their,the sweet spot should be between 2 and 3 turns out.

 

+1 - But the idle mixture screw is going to have minimal effect on gas mileage.

What size jets are installed?
Is the motor stage 1, i.e. high flow A/C and exhaust?
Bike year and mileage?
Has it always had bad mileage or did it just start?
What mileage do you get cruising 60-65 on the highway?

 

I believe they are factory jets, and motor is from factory the 2006 1200 sportster (hope this helps) it has straight pipes on it And it always had bad gas mileage since I got it in June and I get 29MPG, and I also get a lot of back fire from my carb

 

If your getting 29 mpg on the highway, you need to drop the carb bowl and find out what jets are installed.

 

Have you looked at your sparkplugs... they can tell you a lot.

 

At 29 MPG I wouldn't hesitate to pull the carb off. Check the jets and take the slide off the top and pull the needle the quickest way to drop MPG is to shim the needle seats. Clean everything and start over. You should get around 40 even if you flog the hell out of it!

 

your pipes are not helping either...

i would FIRST check for vac leaks... using carb cleaner around the intake seals @ the head... if the engine picks up speed then you have a leak there!

Then i would pull the carb and intake replace the seals and go through the carb make sure of your jets and make sure the CV slide goes up and down smooth... and makes a "woosh" sound... if it just slams shut you may have a problem.
Good slide

bad slide

that should get you on a good path to fix your bike...


BTW if you need parts to clean up the carb or jet it correctly try:
http://www.cv-performance.com/tuners-kits/

 

First thing I'd check would be the plugs. If they're showing a rich condition you'll know to start with the carbs mixture set up (jets, mixture screw, slide, etc.). If the plugs show good or lean, you'll be looking for more of a leak or float adjustment. I've seen guys running with a leak through the drain/vent tube and never noticed anything but the poor mpg.