The operation of the float circuit is conventional. The fuel intake needle is hollow to permit the insertion of a spring and pin. The lip of the float bears on this spring loaded pin, which serves to prevent flooding due to needle chatter, cuased by excessive vibration. The bowl is “balance” vented by means of an external tube which connects the air horn to the air cleaner.
Remove top and turn it upside down allowing the float to rest on the needle & seat.
IMPORTANT: Do not put any pressure on the needle, as damage to the viton tip will cause flooding.
637S – 1/4", 950S – 9/64"
Measure the distance between the bottom of the float and the edge of the casting w/o the gasket. Don’t have the carburetor number? Set it to 1/4".
Adjust the level by bending the tab in the center of the float arm. It is best to bend the tabs with the float off. Remove the float pin, adjust, then put it back on.
Turn the top right side up. The float will hang about 45 degrees. It doesn’t have to be exact. Just make sure the needle comes out enough to allow fuel to flow. Not so far out the needle gets bound up.
Test the needle & seat
Make sure the needle is sealing by letting the float rest on the needle (top upside down), and blow into the fuel inlet. If you suspect any leakage, wipe the viton tip with mineral spirits to clean off any residue.
Heat up some water to just below boiling and immerse the float into the water. The hot water will heat up the inside of the float and if there are any leaks, bubbles will come out of the hole.