give approximately 75 M.P.H. on part throttle. Up to this point of opening only the front carburetor operates except for idle system of rear carburetors as previously described.
Additional movement of accelerator pedal will start to open throttle of rear carburetor. Opening of rear carburetor throttle allows air flow through rear carburetor to open damper valve and bring rear carburetor into operation.
When throttles of both carburetors are fully opened, the front and rear carburetors feed equally.
If accelerator pedal is fully depressed at low speed, only the front carburetor operates until manifold vacuum is sufficient to open flies of damper valve assembly. This will begin to occur at approximately 15 miles per hour.
Damper Valve Lock-Out
A new thermostat lockout has been designed and is attached as an assembly to the rear carburetor damper valve, which controls the cut-in period of damper valve when engine is cold.
The thermostat and bracket is mounted to the damper valve body and extends down over the exhaust manifold and heat from the mani fold operates the thermo spring and times the lock-out release from the damper valve weight pin.
The mounting of lock-out to damper valve assembly is by two screws, the lower hole is used as a pivot, the upper hole is elongated for movement of assembly to get proper adjustment.
The use of the lock-out is to prevent the rear carburetor from operating on cold engines until after the automatic choke on front carburetor has reached its near open position.
Lock-outs are set at the factory so that the thermo spring releases from the lock-out pin on damper valve weight at temperature of 110°+ 2°F. This check can be made in service by removing the damper valve assembly and submersing the lock-out in water of 110°+2°F. Lock-out should not open in water of less than 108° and should be open or clear of the pin at not higher than 112°F.
Operating Check far "Damper Valve Lock-Out Thermastat"
With engine cold drive car on warm-up making full throttle accelerations from 15 to 25 m.p.h. If a light spit or sag in acceleration occurs in the range from 15 to 20 m.p.h., particularly towards the end of the warm-up period, it indicates that the lock-out is releasing too soon. If accelerations are O.K., continue driving for about four miles. Stop and check for release by rotating weight by hand or observing its operation on acceleration. If thermostat has released weight at this time it is not holding on too long.
If thermostat shows out of adjustment, remove assembly and follow instructions for setting in temperature bath.
Gaskets-Carburetor to Manifold
A molded insulating fibre gasket is used between the carburetor and intake manifold on all series. This gasket is same on all series because all carburetor flanges are of "three bolt" type as formerly used on Series 40-50 engines.
On engines with a rear carburetor, this heavy gasket is installed between damper valve assembly and manifold. A thin gasket is used between damper vahle and rear carburetor. See Fig. 6-59.
AIR INTAKE-COMPOUND CARBURETION
(See "Air Cleaner" Section)
Carburetor Throttle Rod Adjustment
The following adjustments cover both single carburetor and compound carburetion equipment. See Fig. 6-59.
1. Floor mat must be in place because mat serves as stop for "open" position of accelerator pedal.
2. If carburetor is not cold enough to cause de-loader cam to contact carburetor lever as throttle is opened, hold de-loader cam in contact with carburetor.