Air cleaner for stratified scavenging two-stroke internal combustion engine

1. An air cleaner for a stratified scavenging two-stroke internal combustion engine, wherein the air cleaner is connected to a carburetor with an air passage and an air-fuel mixture passage to supply clean air filtered by the air cleaner to the air passage and the air-fuel mixture passage of the carburetor, the air cleaner comprising:

an element member provided with a cleaner element for filtering air, an outer circumferential surface of the cleaner element forming an outer circumferential surface of the air cleaner;

an air cleaner base having a first inlet and a second inlet;

a ceiling plate member opposed to the air cleaner base to define a ceiling wall of the air cleaner and;

an air cleaner clean space formed by the air cleaner base, the ceiling plate member and the cleaner element;

a passage forming member forming an extended passage leading to the second inlet,

wherein the passage forming member is shaped to surround a periphery of the first inlet, and

wherein the passage forming member forms a blown-back fuel diffusion preventing region leading to the first inlet,

wherein the blown-back fuel diffusion preventing region is closed by the air cleaner base and the ceiling plate member, and defined by the air cleaner base, the ceiling plate member and a peripheral wall surface of the passage forming member,

wherein the passage forming member has an entrance opening at one end in a longitudinal direction of the passage forming member and an exit opening at another end of the passage forming member,

wherein the entrance opening is opened to the air cleaner clean space, and the exit opening is connected to the second inlet,

wherein the blown-back fuel diffusion preventing region is opened to an air cleaner clean space that is defined by the cleaner element and outside of the passage forming member, and the blown-back fuel diffusion preventing region is opened to the air cleaner clean space through a clearance gap between the entrance opening and the exit opening,

wherein the first inlet is connected to one of the air passage and the air-fuel mixture passage, the second inlet is connected to the other of the air passage and the air-fuel mixture passage.

2. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 1 , wherein the first inlet is located inwardly of the second inlet.

3. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 2 , wherein a ceiling wall of the passage forming member has a concave portion, and the blown-back fuel diffusion preventing region is opened to the air cleaner clean space through the concave portion.

4. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 3 , wherein the extended passage has no turns.

5. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 4 , wherein the passage forming member extends for an entire circumference of the periphery of the first inlet.

6. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 5 , wherein the exit opening of the passage forming member is located adjacent to the first inlet, the exit opening of the passage forming member forms a reflective wall that is adjacent to the first inlet, the reflective wall reflects blown-back fuel coming out of the first inlet toward the blown-back fuel diffusion preventing region.

7. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 2 , wherein the extended passage has no turns.

8. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 7 , wherein the passage forming member extends for an entire circumference of the periphery of the first inlet.

9. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 8 , wherein the exit opening of the passage forming member is located adjacent to the first inlet, the exit opening of the passage forming member forms a reflective wall that is adjacent to the first inlet, the reflective wall reflects blown-back fuel coming out of the first inlet toward the blown-back fuel diffusion preventing region.

10. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 2 , wherein the passage forming member extends for an entire circumference of the periphery of the first inlet.

11. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 10 , wherein the exit opening of the passage forming member is located adjacent to the first inlet, the exit opening of the passage forming member forms a reflective wall that is adjacent to the first inlet, the reflective wall reflects blown-back fuel coming out of the first inlet toward the blown-back fuel diffusion preventing region.

12. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 1 , wherein the extended passage has no turns.

13. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 12 , wherein the passage forming member extends for an entire circumference of the periphery of the first inlet.

14. The air cleaner for a stratified scavenging two-stroke internal combustion engine of claim 13 , wherein the exit opening of the passage forming member is located adjacent to the first inlet, the exit opening of the passage forming member forms a reflective wall that is adjacent to the first inlet, the reflective wall reflects blown-back fuel coming out of the first inlet toward the blown-back fuel diffusion preventing region.