rumpfy
30-05-2013, 02:58 PM
Historically, the car had been performing satisfactorily and was very reliable. In June 2012, a fuel check showed the fuel consumption to be 13.2 L/100K. This was considered to be OK because of the small distances travelled.
In November 2012, on one occasion, the carby flooded due to a sticking needle valve, and the decision was taken to investigate.
Examination of the needle valve showed some rubbing of the needle against the side of its supporting channel. The needle was cleaned up using a diamond file and has continued to perform without sticking since.
The Heated Air Intake and Secondary Diaphragm vacuum motors on the carby were checked and found to be leaking badly. A repair method was developed using a polyurethane coated nylon woven material. The Vacuum motors are now operating satisfactorily.
Following this repair, there was evidence of engine miss when the motor warmed to normal, and it was found the Fuel Cut Vacuum switch on the bulkhead had intermittent contacts and this was repaired. (see postings under Carby Parts Questions by Coldamus)
Checks were done on the ESS and the Fuel Pump Relay and the circuit diagrams traced. Both these items were OK. These modules are built in a form where they can be easily repaired using off the shelf electronic components.
It was found that the fuel consumption was around 18 L/100Km after repairing the vacuum motors.
The Gregeory’s manual gives a comprehensive list of tests which should be carried out on the ‘Carburettor and the Emissions Control' Systems. These tests require the use of a vacuum gauge. In particular, the Bowl Vent Valve (BVV) requires a hand vacuum pump to check vacuum with the engine running.
Initially, it was not possible to check the BVV by sucking (by mouth) on the canister connection because the fuel vapours were so strong.
The high fuel consumption and tendency to miss at engine speeds above about 3000 RPM was a condition which did not respond to any attention. The missing was also evident with car stationary and revving the motor to 3000 RPM and above. It was found that removing the air cleaner (which was new), overcame the high speed miss, and the fuel consumption improved to around 14 L/100 Km.
In the original repairs to the needle valve, it was noted that carbon granules from the canister were lodged in the small diaphragm of the BVV and had worn through the diaphragm. I repaired the diaphragm with a spot of polyurethane (Sikaflex 227?) but the quality of the repair was not known.
After some weeks, the BVV was properly tested and found to be faulty. The diaphragm was leaking and the seal located inside the carby top body was detached from the operating shaft of the BVV.
At this point it MUST be stressed that the BVV CANNOT be removed from the carby top cover UNLESS the top cover is OFF THE CARBY. The pictures don’t quite show the method of assembly of the ‘seal’ on to the BVV operating shaft. In my case the BVV seal had been damaged when its boss was wrenched from the seal outer. I was able to purchase a new BVV. ($45)
To prevent future damage to the BVV diaphragm from bits of charcoal, I rebuilt the charcoal canister (see Posting under Cannister rebuild)
Following the replacement of the BVV, and with NO aircleaner element, the fuel consumption improved again to 12.2 L/100Km. This figure was obtained over 2 tanks of fuel.
I have re-installed the aircleaner element and will check fuel consumption over the coming weeks.
I checked the air pressure loss through the aircleaner system, using a water manometer. This is hard to do accurately, because the result depends on how much airflow is going in to the motor.
The aircleaner cover was in place for the tests and access to the inner vacuum was obtained by connecting the manometer to the crank-case recovery connection on the air cleaner cover.
At an engine speed of 3000 rpm with the car stationary, and with no air cleaner element, the pressure loss through the air induction pipework and aircleaner housing was around 0.75 inches of water.
With the element fitted, the pressure loss was around 1.5 inches of water. So it would seem that the air pressure loss in the element is quite small, and is of the same amount as the pressure loss in the air induction hardware.
Atmospheric pressure is about 33 feet of water, so a pressure loss of even say, 15 inches of water, amounts to about 4 % of atmospheric pressure. This small pressure loss should not cause the fuel consumption to rise to 18 L/100 Km.
I think that the reason for the high fuel consumption maybe related to the faulty BVV. Under normal operation, manifold vacuum from under the throttle, pulls the BVV diaphragm against the spring, and the seal shuts off the bowl containing fuel, from the canister. With a non functioning seal, and the leaking diaphragm, manifold vacuum was coupled through to the top of the fuel in the bowl and sucked directly into the manifold.
The motor was running rich, and this was also evident by the black stain around the exhaust pipe at the rear bumper.
The various vacuum levels inside the aircleaner element, and the manifold and the vacuum ports all around the carby, are part of the carby/emissions system design. All product design work would assume/demand, that diaphragms don’t leak, and everything is according to specifications. However when various components fail and start to function as bleeds or ports and couple various sections of the fuel system together in an uncontrolled and unknown way, then anything can happen. The notion that a new aircleaner element can increase fuel consumption from 14 L/100Km to 18 L/100 km is almost unbelievable; but this did happen.
Will report fuel consumption WITH the element fitted, soon.
In November 2012, on one occasion, the carby flooded due to a sticking needle valve, and the decision was taken to investigate.
Examination of the needle valve showed some rubbing of the needle against the side of its supporting channel. The needle was cleaned up using a diamond file and has continued to perform without sticking since.
The Heated Air Intake and Secondary Diaphragm vacuum motors on the carby were checked and found to be leaking badly. A repair method was developed using a polyurethane coated nylon woven material. The Vacuum motors are now operating satisfactorily.
Following this repair, there was evidence of engine miss when the motor warmed to normal, and it was found the Fuel Cut Vacuum switch on the bulkhead had intermittent contacts and this was repaired. (see postings under Carby Parts Questions by Coldamus)
Checks were done on the ESS and the Fuel Pump Relay and the circuit diagrams traced. Both these items were OK. These modules are built in a form where they can be easily repaired using off the shelf electronic components.
It was found that the fuel consumption was around 18 L/100Km after repairing the vacuum motors.
The Gregeory’s manual gives a comprehensive list of tests which should be carried out on the ‘Carburettor and the Emissions Control' Systems. These tests require the use of a vacuum gauge. In particular, the Bowl Vent Valve (BVV) requires a hand vacuum pump to check vacuum with the engine running.
Initially, it was not possible to check the BVV by sucking (by mouth) on the canister connection because the fuel vapours were so strong.
The high fuel consumption and tendency to miss at engine speeds above about 3000 RPM was a condition which did not respond to any attention. The missing was also evident with car stationary and revving the motor to 3000 RPM and above. It was found that removing the air cleaner (which was new), overcame the high speed miss, and the fuel consumption improved to around 14 L/100 Km.
In the original repairs to the needle valve, it was noted that carbon granules from the canister were lodged in the small diaphragm of the BVV and had worn through the diaphragm. I repaired the diaphragm with a spot of polyurethane (Sikaflex 227?) but the quality of the repair was not known.
After some weeks, the BVV was properly tested and found to be faulty. The diaphragm was leaking and the seal located inside the carby top body was detached from the operating shaft of the BVV.
At this point it MUST be stressed that the BVV CANNOT be removed from the carby top cover UNLESS the top cover is OFF THE CARBY. The pictures don’t quite show the method of assembly of the ‘seal’ on to the BVV operating shaft. In my case the BVV seal had been damaged when its boss was wrenched from the seal outer. I was able to purchase a new BVV. ($45)
To prevent future damage to the BVV diaphragm from bits of charcoal, I rebuilt the charcoal canister (see Posting under Cannister rebuild)
Following the replacement of the BVV, and with NO aircleaner element, the fuel consumption improved again to 12.2 L/100Km. This figure was obtained over 2 tanks of fuel.
I have re-installed the aircleaner element and will check fuel consumption over the coming weeks.
I checked the air pressure loss through the aircleaner system, using a water manometer. This is hard to do accurately, because the result depends on how much airflow is going in to the motor.
The aircleaner cover was in place for the tests and access to the inner vacuum was obtained by connecting the manometer to the crank-case recovery connection on the air cleaner cover.
At an engine speed of 3000 rpm with the car stationary, and with no air cleaner element, the pressure loss through the air induction pipework and aircleaner housing was around 0.75 inches of water.
With the element fitted, the pressure loss was around 1.5 inches of water. So it would seem that the air pressure loss in the element is quite small, and is of the same amount as the pressure loss in the air induction hardware.
Atmospheric pressure is about 33 feet of water, so a pressure loss of even say, 15 inches of water, amounts to about 4 % of atmospheric pressure. This small pressure loss should not cause the fuel consumption to rise to 18 L/100 Km.
I think that the reason for the high fuel consumption maybe related to the faulty BVV. Under normal operation, manifold vacuum from under the throttle, pulls the BVV diaphragm against the spring, and the seal shuts off the bowl containing fuel, from the canister. With a non functioning seal, and the leaking diaphragm, manifold vacuum was coupled through to the top of the fuel in the bowl and sucked directly into the manifold.
The motor was running rich, and this was also evident by the black stain around the exhaust pipe at the rear bumper.
The various vacuum levels inside the aircleaner element, and the manifold and the vacuum ports all around the carby, are part of the carby/emissions system design. All product design work would assume/demand, that diaphragms don’t leak, and everything is according to specifications. However when various components fail and start to function as bleeds or ports and couple various sections of the fuel system together in an uncontrolled and unknown way, then anything can happen. The notion that a new aircleaner element can increase fuel consumption from 14 L/100Km to 18 L/100 km is almost unbelievable; but this did happen.
Will report fuel consumption WITH the element fitted, soon.