Carburetor fuel control
A carburetor fuel flow control device having an elongate annular body received in a cavity with an inlet in its side-wall communicating with a fuel supply passage and an outlet downstream of the inlet and adjacent to an end of the body, and a needle valve with a metering portion adjacent one end rotatably and slidably received in the body with the metering portion at least partially lapping or blocking the inlet to change the effective flow area of the inlet in response to generally axial movement of the needle valve relative to the inlet.
1. A carburetor fuel flow control device, for a carburetor having a mixing passage, a valve cavity, a fuel supply passage opening into the cavity and a fuel outlet from the cavity, the device comprising:
an annular body of a somewhat flexible material having a sidewall and an axially elongate central passage through the body, the body adjacent each end having a circumferentially continuously exterior surface engaging a complementary portion of the valve cavity, an inlet through the sidewall communicating the supply passage with the central passage, and an outlet downstream of the inlet; and
a needle valve having a shank received in the cavity and a cylindrical metering portion slidably and rotatably received with at least a close fit in the central passage and axially movable to at least partially block the inlet to reduce the effective flow area of the inlet into the body passage.
2. The device of claim 1 wherein the cylindrical metering portion has at least a portion with a circumferentially continuous interference fit with a portion of the body upstream of the inlet.
3. The device of claim 1 wherein an exterior circumferential portion of the body downstream of the inlet has an interference fit with a complementary portion of the cavity to provide a seal between them.
4. The device of claim 1 wherein a portion of an exterior surface of the body upstream of the inlet has an interference fit with a complementary portion of the cavity to provide a seal between them.
5. The device of claim 1 wherein at least part of the cylindrical metering portion has an interference fit with the body, and the device further comprises an annular space between the exterior of the body and the cavity with the supply passage and the inlet communicating with the annular space.
6. The device of claim 5 wherein the exterior surface of the body also comprises a circumferentially continuous recess between and spaced axially inwardly from the ends of the body and at least in part forming the annular space between the body and the cavity.
7. The device of claim 1 wherein the central passage and the exterior surface of the sidewall of the body are substantially coaxial.
8. The device of claim 1 wherein the inlet is axially elongate.
9. The device of claim 8 wherein the inlet has a substantially uniform width along an axial length of the inlet.
10. The device of claim 8 wherein the inlet has tapered surfaces configured so that a circumferential width of the inlet increases from the inner surface to the outer surface.
11. The device of claim 10 wherein the tapered surfaces form an included angle in the range of 50 degrees to 70 degrees.
12. The device of claim 1 wherein the inlet is generally rectangular and has a substantially uniform circumferential width along an axial length of the inlet.
13. The device of claim 1 wherein the body also comprises a circumferentially continuous rib adjacent an end upstream of the inlet.
14. The device of claim 13 wherein the rib has an outer circumferentially continuous surface having an interference fit with a complementary portion of the valve cavity to provide a seal between them.
15. The device of claim 1 wherein the central passage merges into a chamfered surface having a maximum diameter adjacent an axially outboard end of the body which is greater than the diameter of the central passage.
16. The device of claim 15 wherein the tool engagement feature of the head has a non-circular configuration.
17. The device of claim 1 wherein the needle valve also comprises a head adjacent an end of the needle valve generally axially opposite to the cylindrical metering portion of the needle valve, and the head is received in the valve cavity and has a tool engagement feature configured so that a screwdriver, socket, or Allen wrench cannot rotate the valve to change the extent to which the cylindrical portion at least partially blocks the inlet to change the effective flow area of the inlet.
18. A carburetor for an engine comprising:
a carburetor body including a mixing passage, a valve cavity, a fuel supply passage opening into the cavity and a fuel outlet from the cavity;
an annular body of a somewhat flexible material having a sidewall and an axially elongate central passage through the body, the body adjacent each end having a circumferentially continuously exterior surface engaging a complementary portion of the valve cavity, an inlet through the sidewall communicating the supply passage with the central passage, and an outlet downstream of the inlet; and
a needle valve having a shank received in the cavity and a cylindrical metering portion slidably and rotatably received with at least a close fit in the central passage and axially movable to at least partially block the inlet to reduce the effective flow area of the inlet into the body passage.
19. The carburetor of claim 18 wherein the cylindrical metering portion has at least a portion with a circumferentially continuous interference fit with a portion of the annular body upstream of the inlet.