From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Ongoing tests and modifications for the Phantom II twin-choke carburettors.
| Identifier | ExFiles\Box 182\M19\ img109 | |
| Date | 28th January 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey} c. to SE. Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to Hy.{Tom Haldenby - Plant Engineer} PHANTOM II TWIN CHOKE CARBURETTERS. Tests have been continued on the twin choke carburetters and we have corrected some of the troubles experienced during our earlier tests. During the first tests we could not get sufficient fuel flow past the float chamber needle valves unless we used a large fuel head - about 12 ft. being the minimum. We have corrected this by increasing the needle valve seats from .125 dia. to .138 dia. The passages from the float chamber to the metering valves gave a low free flow and we have increased these from .172 dia. to .213 dia. as we find the mixture control by means of the variable valves becomes more sensitive when we reduce the resistance of these passages to a minimum. We have increased the power output at speeds above 2000 R.P.M. by increasing the chokes from 1.25 dia. to 1.35 dia. as shown on appended prints. We are next going to try an intermediate choke of 1.30 dia. The power output over the whole range is good giving the usual characteristic of high torque at low speeds. The cold distribution also appears very good. So far we have not done serious work on the accelerator pump and shall leave this until we have proportioned the metering. The pump appears to work as expected but we find the fuel feed to the pump from the float chamber breaks into the float chamber rather near the fuel level and we can get occasions when this passage is uncovered. We have now drilled this passage downwards to well below the fuel level. Although we could get good slow running the metering over the idling range was poor and adjustment difficult. The two adjustment screws next the engine were impossible to operate when the engine was running. We have well explored the existing scheme but are quite unable to obtain adjustment of the mixture to suit both ends of the idling range like we Cont'd............... | ||