Doddy's CB60 Carby Exposure
Exploded Parts Beta Version linked to Doddy's site.
MarkT's populated vacuum diagram for Australian spec
Other Hose Schematics can be found in the PDF engine manual
Secondary Throttle Release Dashpot Location (note starts to move at 2.8psi and full extended at 4.5 psi)
Fuel Pump and Regulator Performance
CB60/61 Fuel Pump Operation Explained
The CB60/61 fuel pump operates via a signal from the tachometer circuit. As an explanatory this is a typical sequence of events:
On start cranking a feed from the starter motor auxilliary provides power to the pump via a normally open relay contact. The normally open contact makes on operation of the starter motor. This is to minimise voltage drop at the pump caused by the heavy starting current of the starter motor. If the engine speed rises above 50 rpm the relay will swap supply to the pump from the starter circuit to the normal fused supply.
The pump relay electronics receive a pulse signal from the ignition coil via a small canned RC tachometer filter mounted behind the carby on the firewall. If the pump relay looses this signal during normal operation, the relay operates after 4 seconds and the pump will stop. It does this because the pulse frequency drops below 2.5 pulses/second (50 engine rpm).
If the ignition is turned to the on position, but the engine isn't running the pump relay will operate after 4 seconds and stop the pump.
Pump specs: 60 litres/hour @ 88.2kPa (12.8 psi) head; 60 litres/hour @29.5kPa (4.3 psi)head. Maximum pressure output 245kPa
CB20/22/23/60/61 Choke Operation Explained
There are two types of choke setups for these engines; manual choke and automatic choke. This is not to be confused with manual and automatic transmissions, we are talking manual or automatic choke operation.
They share pretty much the same vacuum line setup, but the choke plate operates a little differently between versions. The manual unit is a cable operated linkage, that requires the accelerator pedal to be depressed, before or after the choke handle is pulled, for the plate to close. On the automatic unit the plate is closed normally, held there by a choke dashpot and a heat operated actuator.
So how do they work? First we'll look at the vacuum line setup. You will see a thing called a BVSV (bi-metallic vacuum switching valve). It's a simple device that reacts to engine coolant temperature. When the engine is cold the purple fresh air is ported to the yellow choke line and when the engine gets to about 30° its flips the porting so that the green line is ported to the yellow choke line.
So when the engine's cold there is no action on the choke dashpot, but when the engine is hot a vacuum is ported to the dashpot and the choke plate is forced partially open (about 8mm). The jet is installed in the line to allow the vacuum to bleed off slowly when the engine is not operating, ready for the next cold start. The check valve stops the loss of vacuum in the choke line when the there is low manifold vacuum, typically when the engine is under load or boost.
So now we know how that works, we only have to know how the choke plate opens up fully. Well on the manual unit you need to push the choke handle back in and the spring loaded plate will open. On the automatic unit two hot water hoses feed a wax element actuator that extends a small piston once the temperature is up. This piston pushes a ratchet arm that allows the spring loaded choke plate enough travel to fully open.
The standard fuel pump has the following duty:
45 litres/hour at 88 kPa (12.75 psi) head
60 litres/hour at 29.5 kPa (4.3 psi) head
Maximum head : 245 kPa (35.5 psi)
The fuel regulator trys to maintain a higher than boost pressure fuel pressure at the carby of between 25 Kpa (3.6psi) and 34.5kPa (5 psi). This is the difference of the fuel pressure and the pressure in the carby hat.
Probably the best advice here is to buy the kits from Daihatsu. The aftermarket kits from Fuel Miser, Nardek and Akses all seem to have minor variations to standard, such as uncollered pump boots, undersized plungers, etc. The pump boot is a concern as the standard CB60/61 unit has a collar for a spring clip to seal it to the pump plunger stalk and prevent fuel escaping. There has been reports that at least one of these brands include a boot that won't hold against the boost pressure and splits.
The minor rebuild kit from Daihatsu that includes gaskets and spring clips is part No 0421287704000 @ about A$40
The overhaul kit withplunger, needles, gaskets, clips, etc is 0421187729000 @ about A$170