My son just bought a 1981 Sportster. New Dynatec S ignition module fixed the no spark.
Bike now starts right up, plenty of power. Loud after market pipes.
However the bike most of the time will not idle down. Throttle cable
is adjusted to longest length still engine will not idle down. So when
riding their is no engine breaking when you let off the throttle.

The throttle returns fully to idle position. Any ideas?
Thanks.

 

float level possibly, post up a picture of the carb so i can see the specifics on what he is running. thanks.
m

 

Check all your basics - intake leaks etc. That's the kind of carb you need to find someone who really knows it. If you can't - a CV is going to be your new friend.

 

How does the throttle return spring feel? Sometimes these things may pop off and unwind one winding and you have some spring torque but not enough to close the throttle off completely.

 

Stuck float valve , carb floods at idle and then burns off the excess fuel once you get moving then it happens again when you stop . With the engine off , the tap automatically shuts off and you don't see any fuel leak . Usually caused by a minute particle of debris . Thats my best guess .

 

On an 81, the big thing will be manifold leak. Manifold to head is a big one. Rubbers may be gone. I would also pull the carb and make sure that the throttle blades and pivot shaft are tight. IIRC one of the trick to get the Dellorto to deliver fuel well was to drill holes in the throttle blade they may be too big.