drla float level

04/11/13 Dellorto

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dellorto DRLA 36,40,45 & 48.

04/11/13 Dellorto


Diag Part Diag Part No. No. Description Sizes/optionsavailable No. No. Description 1 10527 DRLA36/40 Choke (Venturi) 26,28,30,31,32,33,34,36 43 6581 Spindle nut lock washer 1 10758 DRLA45 Choke 32,34,36,38,39 44 7537 Spring washer 1 11486 DRLA48 Choke 38,39,40,41,42 45 7490 Spindle bearing 2 10078 DRLA 40 Auxiliary venturi No longer available 46 10353 Retaining clip 2 10527 DRLA45 Auiliary venturi No longer available 47 10135 Nut 2 11487 DRLA48 Auxiliary venturi No longer available 48 7413 Choke return spring 3 7484 Main jet 85,90,95,100,102,105,108,110, 49 10252 Choke piston 3 110 to 190 in steps of 1, 190,192,195,198210-240 in 5's 50 10137 Choke actuator cam 4 7644 Idle jet 32-82 in 1's 51 7062 Choke cable bolt 5 10927 Pump jet 30,33,35,38,40,42,45,48,50,55,60 52 10156 Return spring 6 3315 Starter jet 40-90 in 5`s 53 6850 Choke cable washer 7 9164 Main emulsion tube No's 1,2,3,4 54 10110 Drive link 8 7482 Starter emulsion tube No`s 1,2,3,4 55 6432 Choke cable nut 9 7485 Air corrector 80,90,100,110,115,120,125,130,135 56 10231 Cover plate 9 140,142.5-202.5 in2.5`s 205-250. 57 9174 Set screw 9 10304 Tall air corrector jet 160,170,175,180,190,000 58 10140 Choke cable bolt 10 10305 Needle valve (metal) 150,170,200,225 59 7231 Choke washer

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10 10375 Neddle valve turbo (viton) 150,170,200,225cross drilled 60 10817 Choke lever 10 8649 Needle valve, viton tipped 250,270,300,350,400 cross drilled 61 10311 Choke cover 11 10133 Throttle butterfly DRLA 36 62 5011 Lock washer 11 7481 Throttle butterfly DRLA 40 63 4957 Lock washer 11 8010 Throttle butterfly DRLA 45 64 10253 Screw 11 8563 Throttle butterfly DRLA 48 65 2906 Nut 12 10090 Float 66 10928 Pump jet holder 13 10097 Fuel banjo, return 11mm bolt Carb details required. 67 6426 Pump jet holder fibre washer13 12393 Fuel banjo, return 16mm bolt Carb details required. 68 10748 Pump jet Filter/spring 14 10132 11mm banjo bolt Carb details required. 69 6173 O ring 14 12390 16mm banjo bolt Carb details required. 70 7571 O ring 15 10134 11 mm banjo seal 71 10138 Manometer fitting 15 7662 16mm banjo bolt seal 72 8678 O ring 16 10096 Fuel banjo, double 11mm bolt 73 9926 Air bleed screw 17 1419 Fuel Filter 74 9663 Pump diaphragm spring 18 10570 Banjo bolt seal 75 10182 Pump diaphragm 19 6430 Top cover screw 76 10256 Pump cover plate 20 4957 Lock washer 77 5011 Lock washer 21 10066 Top cover Carb details required. 78 6429 Screw 22 10092 Top cover gasket 79 10315 Lock nut 23 6288 Needle seat sealing washer 80 10340 Retaining washer 24 10154 Float hinge screw 81 10332 Spring 25 8498 Retaining clip 82 10331 Sleeve 26 10339 Float hinge screw 83 8260 Retaining washer 27 10738 Idle jet holder 84 9336 Spring 28 7540 Sealing O ring 85 10316 Pump rod 29 7542 Pump non- return valve 86 10686 Retaining clip 30 7513 Cap screw 87 9656 Mixture screw 31 10630 Top cover stud 88 10153 Pump rod clamp 32 7636 Pump jet weight 89 7667 Pump rod clamp screw 33 6415 Pump jet ball bearing 90 8857 Progression blanking cap 34 7540 O ring 91 9754 Screw 35 9754 Throttle stop screw 92 6423 Lock nut 36 7958 Spindle end cover 93 7507 Venturi grub screw 37 10230 Linkage drive arm 94 10790 Butterfly spindle 38 10142 Step washer 95 6416 Throttle butterfly screw 39 10184 Throttle lever 96 10157 Return spring 40 10158 Throttle return spring 97 10183 Throttle lever 41 10130 Washer 98 10229 Throttle lever 42 6423 Spindle nut 99 52534 Gasket set

1. FEATURES

Twin choke downdraft with 36-40-45 mm diameter barrels. Interchangeable chokes from 28 to 38 mm. Butterfly throttle valves. Constant-level float chamber with double float. Starting device with independent circuit. Idle circuit with centrally placed jets and Venturis supplied from the main jets; mixture adjustmentscrews with means for sealing them so as to make them tamper-proof. Main circuit with centrally placed jets and emulsion tubes. Accelerator pump with mechanically-operated diaphragm with single inlet valve and two deliveryvalves upstream from the jets. By-pass screw in each barrel to equalize the air flow to the throttle valves in the idle position. Special design for use on turbocharged engines with pressurized (blown) carburettor.

2. OPERATION

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2.1 - Fuel SupplyFuel arrives at the fuel inlet (15) through the filter (16) and reaches the seat (19) where theneedle (20), anchored to the float (21), adjusts the flow of fuel into the chamber thus ensuring aconstant level of fuel. The float chamber is vented through the hole (4). Any excess fuel sent bythe pump to the carburettor is returned to the fuel tank by the air corrector jet (17) of the fuelinlet (18).

2.2 - StartingWhen the starting throttle (7) is completely open, the fuel, metered by the jet (11), passes intothe emulsion tube (10) where it is mixed with the air coming from the passage (3) and is thenmade to pass through passage (5). Through the two holes (9), the mixture thus formed arrives inchamber (8) where it is further mixed with air coming from passages (22). It is then distributedinto the two channels (12) which reach the main barrels (14) downstream from the throttle valves(13). When the valve is partly open, i.e. when it is desirable to have a leaner mixture, the fuel isfurther mixed with air coming from the hole (6) which is connected with the valve chamber (1)which, in turn, is connected to the atmosphere through hole (2). When the starting valve (7) isclosed the passage between the barrels and the starting device is also closed. In addition, theseparator (23) will close off the two barrels (14).

2.3 - IdlingThe fuel which arrives from the float chamber (34) by way of the main jets (36) reaches the idlingkey (33) through passage (35); it is here mixed with air coming from the air corrector jet (25)and, through channels (24) and (27), reaches the adjustment screw (32). Properly metered, itarrives in the main barrels (14) downstream from the throttle valves (13). With the coupling (50)connected to a vacuum meter it is possible to measure, through channel (51) and the hole (49),the pressure in the barrels (14) with the throttle valve (13) in the idling position and consequentlyto equalize the air flow by turning the by-pass screw (29) which controls hole (30). Thedepression advance take-off is made through the calibrated hole (31) which is connected with thecoupling (28). The screw (26) adjusts the opening of the throttles in the idling position.

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2.4 - Progression

On first opening the throttle valve (13), that is, in passing from idle to top speed, the mixture willalso reach the barrels (14) through the progression holes (48).

2.5 - AccelerationWhen the throttle valves (13) are opened, the lever (46) fastened to the spindle (47), pushes thepump lever (42) by means of the rod (45) and the spring (44). The pump lever operates directlyon the diaphragm (40) against the action of the spring (39). The movement of the diaphragmcauses fuel to be sent to the main barrels (1 4) through the corresponding valves (38) and thethrottle valves (13) are closed, the diaphragm (40) returns to its original position under the actionof the spring (39) and it will once again draw fuel from the float chamber (34) through the valve(41). The delivery of the pump can be adjusted by turning the nut (43).

2.6 - Full Throttle RunningWhen the throttle valves (13) are fully open, the fuel arriving from the float chamber (34) andcalibrated by the jets (36) enters the wells (56) and is mixed with the air metered by the aircorrector jet (54). The mixture thus formed passes through the centering inlet (53) where it isfurther mixed with the air taken in through the main carburettor inlet, arrives in the Venturis (55)and, subsequently, reaches the engine through the main barrels (14).

3. ADJUSTMENT

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3.1 - IdlingAny idling speed adjustment may only be carried out if it is possible to use an appropriate COmeter to measure engine emissions. Only under these conditions is it possible to break the sealsand subsequently to carry out the required adjustments to obtain a correct idling speed. Thebypass screws (c) on the carburettor must be completely closed while the mixture adjustmentscrews must be opened through 5 turns from their completely closed position. Any adjustmentmust always be made with a hot engine and the throttle screws (a) turned until the required rpmsare reached. To equalize the airflow in the two barrels, please consult the instructionsCarburettor Synchronisation and Idle Adjustment. Now proceed to obtain an engine operationwhich is as smooth as possible by turning the mixture screws (b), while still keeping within theprescribed values for engine emissions. Bear in mind that the percentage of CO is increased whenthe screw is turned up whereas it is decreased when it is turned down. If a CO meter is notavailable it is only possible to operate on the throttle adjustment screw (a) so as to obtain thebest idling speed.

3.2 - Accelerator PumpThe adjustment of the accelerator pump must be carried out by placing the carburettor on thebracket with its gasket in place, connecting it up to the fuel tank so that fuel is supplied properly.Put the two 10 cc graduated measuring tubes under the support drain pipes so that all the fuelthat is pumped is collected. Open and close the throttle completely 20 times, with a few secondsbreak in between, and check that the volume of fuel collected in the two tubes is identical andcorresponds to the specifications. Should this not be the case, the delivery of the pump should beadjusted by turning the adjustment nut on the pump control rod, bearing in mind that to increasethe delivery of the pump it will be necessary to turn the nut down, while to decrease it, the nutwill have to be turned up.At this point repeat the checking operation until the exact adjustment is reached.

3.3 - Float levelCheck that the weight of the float corresponds to specification as shown on its body. Check alsothat it is not damaged and that it rotates freely on its pins. Hold the lid in the vertical position sothat the float arm is in light contact with the needle. In this position check that the two half-floats are at the specified height in relation to the float chamber lid with the gasket fitted in the

04/11/13 Dellorto


normal position.

3.1 - IdlingAny idling speed adjustment may only be carried out if it is possible to use an appropriate COmeter to measure engine emissions. Only under these conditions is it possible to break the sealsand subsequently to carry out the required adjustments to obtain a correct idling speed. Thebypass screws (c) on the carburettor must be completely closed while the mixture adjustmentscrews must be opened through 5 turns from their completely closed position. Any adjustmentmust always be made with a hot engine and the throttle screws (a) turned until the required rpmsare reached. To equalize the airflow in the two barrels, please consult the instructionsCarburettor Synchronisation and Idle Adjustment. Now proceed to obtain an engine operationwhich is as smooth as possible by turning the mixture screws (b), while still keeping within theprescribed values for engine emissions. Bear in mind that the percentage of CO is increased whenthe screw is turned up whereas it is decreased when it is turned down. If a CO meter is notavailable it is only possible to operate on the throttle adjustment screw (a) so as to obtain thebest idling speed.

3.2 - Accelerator PumpThe adjustment of the accelerator pump must be carried out by placing the carburettor on thebracket with its gasket in place, connecting it up to the fuel tank so that fuel is supplied properly.Put the two 10 cc graduated measuring tubes under the support drain pipes so that all the fuelthat is pumped is collected. Open and close the throttle completely 20 times, with a few secondsbreak in between, and check that the volume of fuel collected in the two tubes is identical andcorresponds to the specifications. Should this not be the case, the delivery of the pump should beadjusted by turning the adjustment nut on the pump control rod, bearing in mind that to increasethe delivery of the pump it will be necessary to turn the nut down, while to decrease it, the nutwill have to be turned up.At this point repeat the checking operation until the exact adjustment is reached.

3.3 - Float levelCheck that the weight of the float corresponds to specification as shown on its body. Check alsothat it is not damaged and that it rotates freely on its pins. Hold the lid in the vertical position sothat the float arm is in light contact with the needle. In this position check that the two half-

04/11/13 Dellorto


floats are at the specified height in relation to the float chamber lid with the gasket fitted in thenormal position.

drla float level

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