Hi All, New bike owner '90 Sportster 1200. Bought the bike in non running condition. Replaced the coil and ignition sensor (Ultima programable kit 53-660) and it fired right up. RPM's at idle was 4000. Backed off on the idle screw on the carburetor per service manual counterclockwise (maybe 5 full turns) did not make a difference. Also..there is a thumb screw at the top of the carb with a tube coming off that is attached to the bottom of the carb(thumb screw is tightened down clockwise) there is another tube same diameter attached at one end and just is hanging down unattached at the bottom of the frame. Thinking maybe a detached vacuum line from somewhere. Didn't want to let the engine run for any length of time. Maybe 10 sec intervals between backing the idle screw out. I believe the carb was cleaned by previous owner. Think the bike was sitting for a year or so. Any ideas. Thanks V

 

Make sure the throttle cables are adjusted right. Check to see if the throttle plate is closing properly.

 

Yeah I tried to look that up in the service Manuel with no luck. What's the business with the 2 tube's around the carb. Is the one not attached a vacuum line?

 

Did you by chance check cables ???

 

picture would help and is it a stock carb.

 

What card is on the bike? Mikuni HSR carbs have a different idle adjustment. But even then idleing at 4k RPM is likely more than an adjustment problem.

Paul

 

It's an S&S super E carb with some extra lines and a
thumbscrew thingy at the top. I think its some sort of mod. I supposedly adjusted the carb to factory settings and now idles between 3000-5000 rpms. Think I'll try and adjust the throttle free play next. Question...I assume it's not good to run it at that RPM for any length of time. I'll get it started and try n push the choke in...(they call it something else richness adjuster or something) the rpms will drop then it stalls. It's sort of all over the place between 3000 and 5000rpms. The exhaust gets super hot very quickly. Ugh...any thoughts?V

 

what you have is a thunderjet modification which allows one to adjust air flow. it is from zippers performance or it could be a davinci modification.
you will need to lookup tuning info for that modification as it could be your source for the high idle.

 

That carb has a (thingy) Thunderjet installed, which is essentially an addition / addon fuel circuit enhancement to the carb. In terms of the choke, it's an enrichner for starting the engine cold, but should be turned off once the engine has started or it will flood the engine with too much fuel anf foul the plugs.

Can you look in the throat of the cab and see if thg throttle plate is fully closed? Try the cable adjustment, or even remove the throttle cable to eliminate that being the problem with the high idle.

Paul

 

http://www.harley-performance.com/s-...b-upgrade.html

they are similar but you need to know the difference. da vinci goes a few steps ahead.