i have a 510 71 with a L18 weber carb. my car is burning to rich. somethimes when i shut the car off after ive been driving. it chokes and motors stays on for 5 to 10 seconds. then it shuts off. leving smoke coming out of the carb.. some can help me with this issue itll be great thanks.. also when i gas my throttle body shut off vaule doesnt close. i think im missing a spring or sumthing..