FIG 2:1 Type of fuel pump fitted to earlier models. Note that the rocker arms are not shown in housing 6 in group A. Group B is an exploded view of the inlet and outlet valves
2:6 Zenith carburetter, type 32.NDIX
2:7 Servicing Zenith carburetter 32.NDIX
2:8 Solex carburetter, type 40.PII.4
2:9 Servicing Solex carburetter 40.PII.4
All models have a fuel tank under the bonnet, with a remote-controlled tap which has a ’Reserve’ position. Fuel is piped to a mechanical pump on the engine, the pump being driven by a pushrod operated by a cam on the distributor drive shaft. Fuel from the pump is passed to two dual downdraught carburetters, each carburetter feeding a pair of cylinders.
Super-90 and 1600SC cars are fitted with Solex 40.PII.4 carburetters, and all other models under review are fitted with Zenith carburetters, type 32.NDIX. These can be seen in FIGS 2:7 and 2:6 respectively. Earlier cars were fitted with the fuel pump shown in FIG 2:1. Later cars have the pump shown in FIG 2:3 where it can be seen that the pushrod operates the diaphragm by direct means.
Air cleaners are of two types, Zenith carburetters being fitted with an oil-wetted type and Solex carburetters with a casing containing a renewable ’Micronic’ element.
Fuel filters:
Under the fuel tank is the tap and filter shown in FIG 2:5. Note that there is a gauze filter inside the tank which is only accessible when the tank is removed and drained. At 3000 miles and then every 6000 miles, turn off the tap, unscrew the wingnut and remove the sediment bowl 5 and filter 4. Clean bowl and filter and replace. Turn on tap and check for leaks. Renew gasket for bowl if necessary. Do not overtighten wingnut.
The fuel pump is adjacent to the distributor and both types carry a filter under the top cover (see either FIG 2:1 or FIG 2:3). Remove the central bolt and lift off the cover and filter. Clean the parts in fuel and replace. Run the engine and check for leaks. Renew the cover gasket if necessary.
Air cleaners:
The ’Micronic’ element type must be checked at 3000 miles and then every 6000 miles or according to the road conditions prevailing. Release the clips and lift off the top covers. Lift out the elements. If dirty and clogged, renew them. If in usuable condition, tap them and blow away the dust with compressed air. The elements must not be cleaned in solvents, neither should they be boiled. They are fitted in pairs to 1600S engines from 356B.
FIG 2:1 Type of fuel pump fitted to earlier models. Note that the rocker arms are not shown in housing 6 in group A. Group B is an exploded view of the inlet and outlet valves
Key to Fig 2:1
Group A:
1 Top cover
2 Filter
3 Top housing
4 Diaphragm
5 Diaphragm spring
6 Lower housing
Group B:
1 Outlet valve
2 Spring
3 Spring seat
4 Gasket
5 Top housing
6 Valve retainer plate
7 Spring
8 Inlet valve
Cars fitted with a single oil-wetted air cleaner need to have this serviced every 3000 miles, or more frequently if road conditions are particularly dusty. To remove the cleaner, loosen the clamp screws on the clips. Wash the element in petrol and dry off with compressed air or allow to drain and dry. Lightly oil the mesh element, letting surplus oil drain off and then refit the cleaner.
Carburetters:
Every 3000 miles, oil the carburetter linkage and check the flange nuts and fuel pipe connections for security. At the same time, reset the idling and idling mixture screws if necessary. Instructions for this operation are given in Sections 2:7 and 2:9.
Early type with two fixing straps:
To remove tank, close tap and disconnect fuel pipe. Remove splitpin from linkage between tap and control and pull control slightly to rear. Remove vent hose and also wire from gauge sender unit. Release the two straps and lift out the tank. Drain and clean the interior. Do not try to repair leaks with a naked flame or excessive heat as this is extremely dangerous. The only way to remove petrol vapour is by steaming the tank for two hours or immersing it in boiling alkaline solution for the same period.
The air vent hole in the filler cap must be clear. Blow air through the vent tube and the fuel pipe (after detaching it from the pump).
Refit the tank in the reverse order, renewing any felt or rubber packing which may have deteriorated. Also check the rubber grommet for the tap linkage.
Later type with four fixing screws:
To remove, take out tyre, jack and tool kit, then remove rubber pad. Close tap and remove hose. Remove splitpin from tap control and pull control slightly rearwards. Disconnect fuel gauge wire from sender unit. Remove the cover panels and rubber seal at filler neck. Loosen hose clamp on filler neck and remove vent pipe. Remove four screws and lift out tank. Refer to preceding instructions on earlier tank before carrying out repairs.
Refit in reverse order, first checking that cork strip is in good order.
Key to Fig 2:2
1 Delivery valve
2 Suction valve
3 Diaphragm
4 Diaphragm spring
5 Rocker arm pivot pin
6 Rocker arm link
7 Rocker arm
8 Spring
9 Gasket
10 Fibre flange
11 Light alloy intermediate flange
12 O-ring
13 Pushrod
14 Distributor drive shaft and cam
15 Drive gear on crankshaft
Servicing fuel tap:
This is shown in FIG 2:5 and there are only small changes in design over the years. Clean the filter as described at the start of Section 2:2. To remove tap, remove tank and drain it, then unscrew tap. Clean wire gauze filter 6. To check seal 8 if the tap leaks, remove grommet 9 and a circlip inside the tap housing. Use a genuine spare part if the seal is defective.
When refitting the tap, make sure plug 10 lines up with the control. Slacken nut 2 and turn the tap if required.
Servicing fuel gauge sender unit:
This is on the right in FIG 2:5. Before removing it, disconnect the battery and drain the tank. Refit, using a new ’Thiokol’ gasket and check for leaks.
As can be seen in FIG 2:2, diaphragm 3 is pulled down by rockers 6 and 7 when pushrod 13 is moved to the left by the cam on distributor drive shaft 14. The partial vacuum created above the diaphragm causes fuel to enter the chamber by one-way suction valve 2. Spring 4 pushes the diaphragm upwards on the return stroke and fuel is forced out of one-way delivery valve 1 and so to the carburetters. If no fuel is needed, rocker 6 cannot rise and so rocker 7 reciprocates idly. The stroke of the pump can be adjusted by varying the thickness of the gasket 9.
Removing:
Disconnect fuel pipes and remove pump (two bolts in flange). Remove pushrod, fibre flange and gaskets.
Checking stroke:
A gauge is used by service stations (VW.328), but a reasonable check can be made without it. The gauge compresses the actual gaskets used, and as these will not be compressed in the following test, a small allowance should be made. Place the gaskets and intermediate flange on the crankcase flange and fit the pushrod, rounded end inward. Crank the engine and measure the amount of pushrod projecting at each end of the stroke. Measurements should be 29 mm (1.14 inch) and 34 mm (1.34 inch), giving a stroke of 5 mm (.20 inch). Actually the cam should give a stroke of 4 mm (.16 inch) so that the first figures are the maximum permissible. Fit gaskets as required. Do not fit fewer for any reason or the pump diaphragm will be strained.
Key to Fig 2:3
1 Pump
2 Insulating flange
3 O-ring
4 Pushrod plunger
5 Distributor drive shaft and cam
Refit the pump with the same arrangement of gaskets as used for checking. Fill the pump housing with special grease before installing. The oil hole in the intermediate flange must face upwards. When connecting the fuel pipes check the rubber grommet in the engine front coverplate.
Servicing pump:
Refer to A in FIG 2:1. Remove cover 1 and filter 2. Separate housings 3 and 6 (six screws). Press down diaphragm 4 and disconnect it from rocker (part 6 in FIG 2:2). Drive out pin 5 in the same illustration and remove parts 6, 7 and 8. Refer to B in FIG 2:1 and remove plate 6, holding it down to prevent springs 2 and 7 from jumping out. Note the position of valves 1 and 8. Clean all parts in petrol.
Check valve seats and valves for defects. See that diaphragm is sound and check rockers and pin for wear. If possible, check spring against a new one. A weak spring may cause low fuel delivery with poor engine performance and a spring which is too strong may cause carburetter flooding.
Reassemble by fitting valves and springs. Red face of valve contacts seat. Check action by sucking and blowing. Assemble rockers and pin. Fit spring and diaphragm, connecting pullrod with rocker link. Press rocker arm inwards until it is 35 mm (1.4 inch) from the mounting flange and hold it while fitting the top housing. Tighten the screws diagonally and evenly. Fit cover and filter, using a new gasket if the old one is hard and cracked. Fill the rocker housing with antifreeze grease.
This is the type shown in FIG 2:4. When installed the pump is horizontal. It is fitted to 356B and C engines of types 1600,1600S and 1600S.90. The action is similar to that described for the earlier pump (see Section 2:4), but the pushrod or actuating plunger is linked at one end to the diaphragm and the other end bears directly on the cam (see FIG 2:3).
Key to Fig 2:4
Group A:
1 Cover bolt
2 Gasket
3 Cover
4 Gasket
5 Filter
6 Upper housing
7 Leaf spring
8 Valve stop
9 Self-tapping screw
10 Flange screw
Group B:
1 Diaphragm assembly
2 Coupling pin
3 Plunger
4 Spring
5 Lower housing
6 Plunger spring
7 Retainer
8 Lock ring
Removing:
Pull off fuel hoses, remove shield and release pump (2 nuts at flange). Note insulating spacer under flange.
Dismantling:
Refer to FIG 2:4, A and B. Remove cover 3 and filter 5 (see A). Separate the housings (six screws). Refer to B, rest diaphragm 1 downwards on bench and press retainer 7 down with pliers. Remove lockring 8 and spring 6 with the retainer. Remove burrs from ring groove in plunger 3. Withdraw diaphragm and plunger assembly. Punch out pin 2 to separate the plunger and diaphragm. Referring to A, unscrew self-tapping screw 9 from housing 6 and remove spring 7 and stop 8. The outlet valve is pressed in and cannot be removed. Clean all parts with petrol and check for corrosion and wear. Renew the diaphragm if hardened or worn. Suck and blow to check action of valves.
Reassemble in the reverse order. Centralize the pin in the plunger and check freedom of action. Ensure diaphragm is not creased when tightening the six screws evenly and diagonally. Renew cover gasket if leaking.
Key to Fig 2:5
1 Gasket
2 Retaining nut
3 Pipe for outlet hose
4 Filter
5 Sediment bowl
6 Filter inside tank
7 Fuel outlet to tap
8 Tap seal
9 Rubber cover
10 Plug
This is fitted to all 356A engines from September 1957 to September 1959. It is fitted to all 356B engines in the 1600 and 1600S class except the 1600S 90 which has the Solex carburetter covered in Section 2:8. 356C engines in the 1 600C class also have this carburetter but the 1600SC has the Solex carburetter. There are, of course, two carburetters to each engine.
Description:
Features of the carburetter are shown in FIG 2:6. There are two barrels, two throttle valves and two floats. An accelerator pump supplements the main supply of mixture when sudden demands are made on the engine.
Action is as follows. For idling refer to FIG 2:8. The idling jet meters the fuel, the air jet provides the correct amount of air and the mixture regulating screw controls the quantity of mixture delivered to the engine. In addition, there is an idling adjustment screw which controls engine speed by altering the throttle opening.
For main carburation, refer to FIG 2:9. Each barrel has a mixture tube holder carrying a mixture tube, an air correction jet and a diffuser. The two main jets are housed under a cover on the side.
The fuel and air mixture is determined by the main jet which meters fuel, the air correction jet which meters compensating air as engine speed increases and a venturi which controls the volume and speed of intake air. Fuel reaches the main jet from the float chamber.
The action of the accelerator pump is shown in FIG 2:10. The pump plunger moves in a cylinder which communicates with the float chamber. The plunger is operated by a linkage to the throttle shaft. When the throttles are closing the plunger moves up and draws in fuel through a suction valve. When the throttles are opened, the plunger moves downward and fuel is forced through a pressure valve and out through jets situated above the barrel venturis. Sudden opening of the throttles causes a plunger spring to compress and store up energy for a longer injection of fuel. Quantity of fuel injected is controlled by pump stroke which is adjusted at the linkage.
Key to Fig 2:6
1 Main jets
2 Idling jets
3 Air correction jets
4 Idling air jets
5 Injection tube jets
6 Floats
7 Float needle valve
8 Accelerator pump plunger
9 Idling mixture screws
10 Jet chamber cover
11 Idling speed adjustment screw
12 Throttle lever
Key to Fig 2:7
1 Cover screw
2 Enrichment nozzle
3 Float needle valve
4 Fuel inlet bolt
5 Cover
6 Gasket
7 Accelerator pump nozzle
8 Body
9 Idling jet
10 Float level adjustment
11 Accelerator pump
12 Pump adjustment
13 Pump lever
14 Pump rod
15 Main jet carrier
16 Idling mixture screw
17 Idling speed adjustment screw
18 Throttle shaft
19 Thrust plate
20 Throttle lever
21 Accelerator jet
22 Primary venturi
23 Air correction jet
Removing:
Close fuel tap and disconnect pipe from carburetter. Loosen and remove control rod from throttle lever (see FIG 2:11). Release carburetter (4 nuts) and lift away. Cover the inlet manifold.
Dismantling:
At opposite side to throttle lever, release pump spring and linkage (spring clip). Remove screws and lift off cover. Prise up toggle lever and remove dual floats. Remove fixing screw and lift off mixture tube holder shown in FIG 2:11 after loosening the air correction jets. Remove the air jets and tap out the mixture tubes.
Unscrew the idling air jets and pump jets. If necessary, the injection tubes can be pressed out using a screwdriver as a lever on a block of wood in the venturi. Put plastic tubing on the screwdriver blade to protect the injection tubes. The illustration shows the cover removed to expose the main and idling jets. Remove these and the idling mixture screws.
Cleaning and inspection:
Clean all parts in petrol. Use compressed air to clean the jets, or failing this, a tyre pump. Never clean jets with a needle or wire. Check cover gasket. Check float needle valves for smooth seats and good gaskets. Immerse floats in hot water. Bubbles will indicate a leak. Pump plunger must be renewed if worn and scored. Check all jets against correct sizes given in Technical Data. Look for a worn throttle shaft or body. Air leaks at this point will weaken mixture strength and give idling and starting troubles. Check idling screws. Tips must be straight and unbroken.
FIG 2:8 How idling mixture is produced on Zenith carburetter 32.NDIX. Fuel is represented in solid black or as an emulsion with white dots
Assembling:
This is done in the reverse order. If the venturis were removed, fit them so that the lettering faces upwards. Do not overtighten the securing screws.
Checking float level:
The Porsche special tool for this operation is P.77 and consists of a clear plastic measuring glass which can be fitted to the float chamber fuel outlet. If the use of the tool cannot be obtained it might be best to ask an agent to make the check. Before doing this, check that trouble with flooding or poor engine performance is not due to badly adjusted floats. To do this, remove the float assembly and stand it on a flat surface to see that both floats and the bracket touch. If necessary, set the floats carefully. Refit the assembly and check that the floats do not touch the sides when moved up and down. Also check the needle valves as described in the preceding instructions.
Idling adjustment:
There is a synchronizing unit which is tool No. P.75 but a reasonable check can be made using a length of rubber tubing. The object is to ensure that both carburetters are working correctly.
Run the engine up to operating temperature and remove the air cleaner(s). Detach throttle rods from levers. Tighten idling adjustment screws on throttle levers until engine reaches about 1000 rev/min. Gently close both sets of idling mixture screws (see FIG 2:11). Reopen about 1½ turns. Now open or close the screws uniformly to give the highest engine speed with smooth running. The screws must never be in the fully closed position. Reduce engine speed to 650 to 750 rev/min by turning the idling adjustment screws. Put one end of the rubber tubing to the ear and hold the other at each carburetter intake in turn. Note the intensity of the hiss. A synchronizing device will enable setting to be done accurately, but careful work with the tubing will enable a fair setting to be made. Adjust the idling mixture screws to achieve the best results.
When satisfied, adjust lengths of throttle rods so that they can be fitted without tension and check that throttle opening is synchronized by listening with the tube. Reset the idling speed if necessary.
Further checks which can be made at the same time to ensure correct synchronization and throttle movement include running the engine at 1200 to 1300 rev/min and checking that throttle opening is uniform for both carburetters by listening with the tube. Adjust throttle positions as required by means of the operating rods. Also check the stop screw on the accelerator pedal. When the pedal is fully depressed there must be a clearance of about 1 mm (.04 inch) between throttle stops and abutments on carburetter bodies.
If there is difficulty in setting the idling mixture correctly, suspect faulty idling mixture screws, worn throttle butterflies and spindles or ignition and mechanical troubles.
Checking accelerator pump:
The action of the pump is shown in FIG 2:10. The test is made to find how much fuel is delivered at the injection tube, and it needs a small receptacle which can be inserted under the end of the tube, and a suitable measuring glass. Then roceed as follows:
1 Adjust for correct idling and run the engine until the float chamber is certain to be full of fuel. Stop engine and remove air filter(s).
2 Work the throttle lever and watch the injection tube, continuing the operation until all bubbles disappear.
3 Hold the receptacle under the injection tube and work the throttle lever twice from stop to stop. Measure quantity collected, then repeat operation as a check. Correct volume is .2 to .3cc for two injections. On 356C (1600C) engines use a figure of .25 to .35cc.
4 To adjust delivery, alter the length of the pump rod as shown in FIG 2:12. Note that the pump jet cannot affect the injection quantity. The only criterion is that injection time and volume should be the same for both carburetters.
FIG 2:9 How mixture is produced at full throttle on Zenith carburetter 32.NDIX. Solid black represents fuel; or with white dots, an emulsion of air and fuel
FIG 2:10 How the accelerator pump works on Zenith carburetter 32.NDIX. Solid black represents fuel; or with white dots, an emulsion of air and fuel
FIG 2:12 To alter volume of fuel injected by pump, adjust length of pump rod on Zenith carburetter 32.NDIX
Checking throttle valves:
Hold carburetter horizontally and subject throttle butterfly valves to a light test. The valves must close uniformly and there must be no excessive wear. If the valves do not close together it is possible to twist the throttle shaft until they do, but be careful when performing this operation. The throttle assembly can be detached by removing the four screws from the mounting flange. Check gasket and idling bores for obstruction.
The inlet manifold:
After removing the carburetter(s), remove the manifold(s) by taking off the sparking plug leads. Remove the vertical side duct plate then remove the manifold. Cover the inlet ports. When refitting, the graphited face of the gasket goes on the cylinder head.
Accelerator linkage:
To remove, unhook ball joint on accelerator pedal and remove pedal. Remove the adjacent half floorboard. Remove and detach ball joint from long accelerator rod. Detach short rod from bell crank at fan housing. Jack up rear of car, detach long rod from bell crank on transmission and remove by pulling to the rear.
When installing rods, grease the joints and bell crank spindles. Tighten locknuts on ball joints. Check throttle operation as described at the end of the preceding section on idling adjustment.
These twin-throat carburetters are fitted to 1600S.90 and 356SC engines. The main features can be seen in FIG 2:7.
Description:
The main body has two intake barrels, each having independent idling and power mixture systems with an accelerator pump 11 to supply enriching fuel to both barrels. The throttle valves are mounted on a common shaft 18. An adjusting screw 10 makes the setting of fuel level in the float chamber a particularly simple operation. Action of the carburetter is as follows:
For idling, refer to FIG 2:13. Fuel is drawn through main jet Y and idling jet g after which it mixes with air from air bleed u to become a mixture that passes onto adjustable control screw W and three other very small apertures adjacent to the throttle valve at small openings. Unscrewing the control screw enriches the mixture. Screwing it in weakens the mixture.
For main carburation refer to FIG 2:14. Fuel passes main jet Gg and proceeds to emulsion tube S where it is emulsified with air from correction jet a. Depression in the intake barrel draws this mixture into primary venturi X to be atomised still more by intake air in venturi K. At full load conditions with high rev/min, still more fuel is needed and this enrichment is provided by jet q2 and nozzle q1.
For the enrichment needed during sudden acceleration there is a diaphragm pump as shown in FIG 2:15. When the throttle valve is opened, pump rod T and lever L5 actuate the diaphragm so that fuel is forced through jet Gp. It passes check valve H2 and is injected into the main venturi through nozzle i. Check valve H2 stops air from being drawn back into the system when the diaphragm retracts. Check valve H1 stops fuel flowing back into the float chamber on the pressure stroke. It incorporates a tiny relief hole to prevent excessive enrichment, depending on the speed of diaphragm movement.
FIG 2:13 Producing an idling mixture on Solex carburetter 40.PII.4. Solid black represents fuel; or with white dots, an emulsion
Key to Fig 2:13
u Idling air jet or bleed
g Idling jet
Y Main jet
W Idling mixture screw
Removing and refitting:
1 Close fuel tap. Remove air cleaners. Detach fuel pipes and throttle rods from carburetters. Remove flange nuts and lift off carburetters.
2 Cover intake ports.
3 Refit in reverse order, using new gaskets. Tighten flange nuts diagonally and evenly. Adjust throttle rods so that valves open fully.
Dismantling:
Refer to FIG 2:7 and do the following:
1 Remove cover 5 (screws 1). Remove float, pin and intermediate swivel.
2 Remove accelerator pump 11. Remove main jet carriers and jets 15.
3 Remove idling jets 9 and idling air bleeds. Remove air correction jets 23 and shake out the emulsion tubes. Remove retaining screws and nozzles 7, taking care not to bend them. Remove pump jets 21 and also the check valve.
4 Remove enrichment nozzles 2 and mixture screws 16. Remove securing screws and twist venturis 22 out of barrels. Remove securing screws and twist out the main venturis. The venturis need not be removed unless absolutely necessary, but if they are, file off any burrs raised by the retaining screws.
FIG 2:14 Producing main supply of mixture on Solex carburetter 40.PII.4. Solid black represents fuel; or with white dots, an emulsion. Full throttle enrichment is supplied by jet q2 and nozzle q1
Key to Fig 2:14
Y Main jet carrier with jet Gg
K Main venturi
X Primary venturi
q1 Enrichment nozzle
a Main air correction jet
s Main emulsion tube
q2 Enrichment jet
Q Enrichment fuel supply
Key to Fig 2:15
i Injection nozzle
H2 Check valve
Gp Pump jet
m Diaphragm spring
M Pump diaphragm
H1 Check valve
T Pump rod
t Pump adjustment
L5 Pump lever
Cleaning and inspection:
Use clean fuel in a container and wash all parts. Do not push wire through jets to clean them but use compressed air. Check needle valve assembly 3 and renew if valve seat is shouldered or there has been trouble with flooding. Immerse float in hot water to check for leaks as indicated by a stream of bubbles. Make sure replacement float has correct weight of 7.4 gm.
If pump diaphragm has hardened and cracked, renew it. Renew all faulty gaskets. Check jets sizes against those given in Technical Data. When renewing parts use genuine Solex spares which are accurately calibrated. Check throttle spindles and bearings in body. Excessive wear at these points will lead to weak mixture problems. Tips of idling mixture screws must not be bent or broken.
Reassembling:
Reverse the dismantling instructions. Fit main venturis so that lettering faces upwards. Do not overtighten venturi retaining screws.
Adjusting idling:
Although Special Tool P.75 is the best means of synchronizing carburetters, a length of rubber tubing can be used to obtain a reasonable result. Adjust the idling as follows:
FIG 2:16 Section through float chamber on Solex carburetter 40.PII.4, showing float level adjustment
Key to Fig 2:16
1 Vent
2 Needle valve
3 Cover
4 Fuel inlet
5 Inspection plug
6 Float
7 Float level adjustment
1 Let engine run up to operating temperature and remove air cleaners. Detach throttle rods from carburetter levers. Turn idle adjustment screws 17 until engine idles at 1000 rev/min (see FIG 2:7). Turn idling mixture screws 16 right in without force and back off 1½ turns. Now turn screws in or out to get the fastest idling speed. Never leave the screws turned fully home.
2 Turn the adjusting screws 17 so that the idling speed drops to 800 to 900 rev/min. Take the rubber tube and place it adjacent to one intake barrel and listen to the hiss by placing an ear to the other end. Move to a similar position on the second barrel and compare the hiss. If they are not the same intensity the throttle valves are not synchronized. Adjustment is made by carefully twisting the throttle valve spindle.
3 Repeat the preceding operations on the second carburetter, trying to achieve the same intensity of hiss throughout. Any change in idling speed calls for readjustment and a further check for synchronization.
4 When satisfied, reconnect the throttle rods, altering the lengths so that they fit without tension. Run the engine at 1200 to 1300 rev/min and recheck the synchronization. Adjust the throttle rods if there is a variation, then recheck the idling speed.
5 Check that when the accelerator pedal is fully depressed against the stop screw the carburetter levers clear the stop blocks by about 1 mm (.04 inch). Adjust the pedal stop screw if necessary.
Adjusting accelerator pump:
Run the engine at correct idling speed until the float chamber is full. Stop engine and remove air cleaners. Work throttle lever until no more air bubbles emerge from pump nozzles 7 (see FIG 2:7). Hold small receptacle under a nozzle and move throttle lever rapidly twice from stop to stop. Check quantity of fuel collected. It should be .45cc in the warm season and .65cc in the winter. Repeat on second nozzle and then check the second carburetter. Adjust by altering nut 12 on pump rod 14. If there is no further adjustment, put a spacing washer under the nut.
Key to Fig 2:17 1 Nozzle
2 Primary venturi
3 Main venturi
4 Carburetter body
5 Correct path of fuel
6 Throttle valve
FIG 2:18 Latest accelerator rod and bell crank. Flexible insulator 3 reduces transmitted vibration. Redesigned bell crank on transmission gives smoother operation at low throttle openings
Key to Fig 2:18
1 Bell crank
2 Accelerator rod
3 Flexible insulator
4 Rod to accelerator pedal
5 Crank spindle
6 Ball joint
FIG 2:19 Adjust bell crank on fan housing as shown (top left). Correct position of transmission bell crank (top right). Move stop A when adjusting hand throttle (bottom view)
Check that the jet of fuel passes through the slit of the opening throttle valve as shown in FIG 2:17. The tip of nozzle 1 must always be at the original height if any attempt is made to alter the direction of the jet by bending the nozzle.
Note that the size of pump jet does not affect the volume of fuel injected, only the time it takes. The quantity and the time must be the same for both carburetters.
Checking float level:
Before altering the float level make sure that trouble has not been due to a faulty float, or needle valve. If the official float level gauge P.78 is not available, proceed as follows:
Stand the car on level ground and start the engine. Refer to FIG 2:16 and remove plug 5. If the level is correct, fuel will be seen, and it might just begin to emerge. If fuel is not seen or if it pours out, adjust at screw 7. Turning screw in will lower fuel level and unscrewing it will raise the level. The operation or adjustment needs some care because turning the screw inwards will make the float drop and displace fuel out of the inspection plug hole. Let the engine consume any surplus fuel before deciding whether further adjustment is needed.
The modified accelerator rod on later cars is shown in FIG 2:18. It incorporates a flexible connector 3 which eliminates transmitted vibration. The included angle of the bell crank levers was also increased to give slower throttle opening at low speeds to give better control.
The adjustment of the linkage to give the best results is as follows:
1 With the linkage correctly adjusted as described in Section 2:7 make further adjustments to the bell crank on the fan housing. The centre of the ball joint on the long lever must be 50 mm (1.95 inch) from the face of the housing, as shown in FIG 2:19 (top left). Note that the long lever is now parallel to the accelerator rod.
2 Adjust the rod between the bell crank on the fan housing and the one on the transmission so that the distance between the spindle centre and the ball joint is 20 to 21 mm (.78 to .82 inch) as shown on the right in FIG 2:19.
3 Adjust rod from transmission bell crank to accelerator pedal so that the ball joint can be pressed together without tension. Adjust pedal on the linkage so that the distance from the upper edge of the pedal to the floor is about 80 mm (3⅛ inch).
4 When the pedal is fully depressed, make sure that the carburetter throttles are not strained. Clearance at the throttle stops should be 2 to 3 mm (.08 to .12 inch). Adjust pedal stop screw if necessary.
Hand throttle adjustment:
The bottom illustration in FIG 2:19 can be used for reference. Warm up the engine. Slacken clamp A on the inner cable. Pull hand throttle knob slowly until the tachometer registers 2500 rev/min. Turn the knob clockwise to lock it. Set the clamp to touch the stop on outer cable.
(a) Restricted flow, or no fuel from pump
1 Air vent in tank restricted
2 Fuel pipes blocked, tap restriction
3 Pump or tank filters blocked
4 Pump diaphragm defective
5 Diaphragm spring broken
6 Faulty valve assembly in pump
7 Worn rocker pivot, pushrod or cam
8 Fuel vaporizing in pipelines due to heat
1 Check (a)
2 Sticking float needle valve
3 Float level set too low
(c) Float chamber floods
1 Defective float needle valve
2 Float level set too high
3 Punctured float
(d) Excessive fuel consumption
1 Check (c)
2 Carburetter out of adjustment, wrong jets
3 Fuel leakage
4 Dirty air cleaners
5 Pump delivery pressure too high
6 Brakes binding
7 Tyres too soft
8 Idling speed too high
9 Car overloaded, fierce driving
(e) Poor idling
1 Check (c)
2 Wrong idling adjustment
3 Idling jet or air bleed blocked
4 Leak in inlet manifold system
5 Worn throttle valve and spindle
6 Damaged idling mixture screw
(f) Difficult starting
1 Check most of preceding sections
2 Faulty ignition
3 Mechanical defects in engine
(g) Hesitation or flat spot
1 Idle settings too lean
2 Wrong float level
3 Incorrect accelerator pump setting
4 Weak mixture due to wear or air leaks
