CARBURETOR: BASIC PRINCIPLES

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Filed Under (Tips and Review) by admin on 16-11-2010

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On the right, the main components of a Dell’Orto motorcycle carburetor are shown: 1. starting lever; 2. air intake; 3. venturi; 4. starter jet; 5. float chamber; 6. atomizer; 7. fuel valve; 8. needle; 9. throttle valve; 10. float chamber air intake; II. fuel connection; 12. Idle mixture adjusting screw; 13. throttle valve adjusting screw; 14. float; 15. idle emulsion tube, 16.idle jet; 17. main jet. This is a diagram of the gasoline delivery in the inducted airflow: the fuel inside the float chamber rises in the atomizer (31), going through the jet (32) which adjusts the delivery together with the needle (28); the liquid is emulsified first with the air arriving from the channel (13) inside the nozzle (30) then going into the venturi (29) it mixes with the air coming from the intake

Ural carburetors Installation and idle adjustment

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Filed Under (Ural) by admin on 02-11-2010

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1. First you must adjust the idle. It is acceptable per the manual to adjust the idle by using the idle adjust screws (11). This usually involves screwing them then backing out 1 to 1.5 turns. Or you can adjust looking at the sliders 2. If installing the carburetors: a. Remove the cover (2) b. Reomve the slider (3) c. Place the throttle cable through the guide (18) with the spring (4) on the cable. d. Route the cable through the slide catch (6) e. Insert the slide assembly into the chamber and make sure it easily slides up and down. Direct the needle (8) into the opening of the diffuser (angled side visible). f. Screw assembly together and verify via throttle movement that slide moves freely. Attach fuel delivery lines to (12). 3. Using the idle set screw (11) raise the slider so the lower edge is 1-2 mm. 4. Assemble to engine using the proper gaskets (paper – felt – paper). 5. Using the locknut (26) adjust the free play of the throttle cable (2-3 mm) 6. Adjust the idle mixture screw – turn in completely then out 1 to 1.5 turns 1. Remove one of the spark plug caps, and with the cap shorted, adjust (11) to decrease RPM’s to a point of being minimally steady. 2. Adjust the mixture (15) out until RPM’s decrease. Turn in until RPM’s increase slightly. Then turn in screws ΒΌ to 1/3 revoultion. 3. Do the same for the second carburetor with the first spark plug cap shorted. 4. With both cylinders, adjust each idle (11) on each carburetor the same amount each until it’s at a steady, minimal RPM. Use small changes. (at this point you can use your airflow tool to check). 5. Sharply increase, then decrease throttle. Then engine must return to low RPMs smoothly. If the engine goes below limits, readjust (11) from step 4. Synchronization of the K68 Note: Rather than using the opposite cylinder shorted to test the pull of the live cylinder carburetor, you can use something like a Twinmax connected to the test ports (27 Fig 1). Or, if you have a model without these ports, use a Synchrometer (Appendix 2) held against the face of the carburetor. These tools merely show airflow passing through each carburetor (which is dependent on the position and wear on the slide). If using these tools, it’s not necessary to do the following steps. You wil want to use a throttle guide (Appendix 1), to show airflow at various throttle settings. Using the flow meter of your choice make sure each carburetor is the same at the various throttle settings. 1. Place the motorcycle on the center stand ensuring the rear wheel is suspended 2. Make sure you have large area to work with (safety issues here) 3. Shift into the highest gear with the engine running 4. Short one spark plug cap to the cylinder (using a nail or something in the fins) 5. Increase the speed to 40-50 km/hr 6. Fix the throttle using the throttle (maybe using a throttle stop screw under the throttle housing). 7. Reconnect other cylinder and using the opposite carburetor determine the speed which should be the same as the first. 8. Adjust the position of this slide to achieve the referenced speed using the locknut at the top of the carburetor.

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