I recently got a 75 Harley Davidson Sportster xlh 1000 electric start and I need to know how to adjust the carburetor mixture it has the Bendix zenith with only one screw on top for adjustment and the idle speed screw???

 

get the engine warmed up, slowly turn the screw on top in until the engine starts to stumble, then back out the screw about a 1/4 -1/2. adj the idle to your liking, and maybe repeat. Pull off the bowl and there you will find the main jet.