Patent ID: 7428891

Claim:
An outboard motor comprising an internal combustion engine with a carburetor having an intake passage, a butterfly-type throttle valve placed in the intake passage and a low-speed system having bypass ports and idle ports opening into the intake passage, said butterfly-type throttle valve comprising a valve plate having a first valve part that turns from a downstream side to an upstream side with respect to an air intake direction in the intake passage when the throttle valve is opened from a fully closed position, and a second valve part that turns from the upstream side to the downstream side with respect to the air intake direction when the throttle valve is opened from the fully closed position; wherein the first valve part of the valve plate has an edge that moves from the downstream side to the upstream side past the bypass ports when the throttle valve is opened from the fully closed position, and the second valve part of the valve plate is provided with a through hole that allows air to flow therethrough at a flow rate necessary for idling when the throttle valve is at the fully closed position; wherein the throttle valve is configured so that the through hole in the valve plate remains fully open and unobstructed in all positions of the throttle valve; and wherein the through hole is formed in a portion of the valve plate which is spaced away from the bypass ports, whereby fuel discharge through the bypass ports is substantially unaffected by pressure adjacent the through hole during engine operation.