Intake

From Tw200

87-01 Carburetor
Pre_02 TWs do not have the CV carb. The CV is easy to identify. It has a round 2.5” black plastic top piece. The older carb, 87-01, has a cast metal top looking like an over turned bathtub. 
    Stock US jetting is #114. idle jet is  #40
    The bike will benefit from resetting the airscrew, found on the bottom under a brass cover on the motor side of the carb. 1.75 to 2.5 turns out seems to give good results.
    Most bikes will run well with the stock jetting as long as the carb is clean. #116 and #118 jets are common changes.  Bikes running at higher altitudes will need a smaller number jet, such as #112
    The most common problem with the carburetor is clogging up from sitting over time with gas still in the bowl. Prevent this by draining the fuel bowl anytime the bike sits for a month or more. This is done using the small Philips screw at the bottom of the bowl, seen from the left side of the carb. Gas will run out the drain tube until the bowl is empty.  Bikes with clogged main jets may run on choke but will stall with no choke even when warm. A lean running bike may run so hot the head pipe will glow red from the heat.

    The rubber air boots on both sides of the carb get hard with age. The motor side one will crack and cause your bike to run lean. The air box side will shrink and will not fit over the carb intake. 

    Do not re-jet your bike unless you start with a clean well running bike.
    Anything you do to “improve” the airflow will make your bike run lean and lower you mpg and usable horsepower. More air = more gas. Increased airflow will call for larger jets.

    The fuel is delivered to the motor in three over lapping stages.  The first third is from the idle jet giving away to the needle jet (the silver needle hanging inside the carb), and them at the top speeds the main jet.