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Rochester H, HV Carburetor Adjustments

Idle Speed & Mixture
For preliminary setting to warm up engine, turn idle mixture screw on each carburetor 3 turns out from lightly seated position. With engine idling at normal operating temperature with choke valve wide open and fast idle not operating, set automatic transmission to Drive. Adjust idle speed screw on each carburetor for correct hot engine idle speed, adjust idle mixture screw on each primary carburetor (turn in) until engine drops off 20-30 RPM from maximum RPM point, then turn each screw out 1/4 turn. Recheck the idle speed.

Idle speed
Automatic TransManual Trans95 & 110 HP600 RPM trans in drive.700 RPM140 HP550 RPM trans in drive.650
Fast Idle 
Make this adjustment after final idle mixture and RPM have been made. Stop the engine and place throttle lever tang on 2nd highest step of fast idle cam. Check clearance between end of idle speed screw and throttle lever. If clearance is not correct, adjust by bending throttle lever tang as necessary. 

Adjusting off vehicle
Position idle speed screw as follows: With throttle lever in closed position, turn idle speed screw in until firm drag secured on paper strip placed between screw and throttle lever, then turn idle speed screw in an additional 1 1/2 turns. With idle speed in this position, check fast idle as above.
Carburetor Parts

Pump Rod
Back out the idle speed screw until the throttle valve is completely closed, then bend pump rod as necessary to align index mark on upper pump lever with sharp edge of air horn casting.

Idle Vent Valve 
Close throttle valve to the point where vent valve just begins to open. At this point, measure throttle valve opening by inserting gauge of correct size between valve and bore directly opposite idle mixture screw. If throttle opening not correct, bend tang on throttle lever as required. Be careful not to bend vent valve spring arm.

Vacuum Break Diaphragm
Press diaphragm plunger inward until seated, close choke valve to point where connecting link is at end of slot in choke lever. Check choke valve opening by inserting gauge of correct size between lower edge of valve and air horn wall. Adjust by bending connecting link at the angle as shown.

Float Level
With air horn inverted so that weight of float is holding needle valve closed, and with gasket in place, measure from gasket surface to bottom of each float. Adjust by bending the float lever tang, which contacts inlet needle. Bottom of floats should be parallel with air horn surface. Floats should also be aligned to prevent interference with the sides of the float bowl when installed.

Float level: 1 1/16″

Float Drop
With the air horn upright so that floats hang freely, measure from the gasket surface to the bottom of float at toe or free end. Set by bending the tang at rear of float arm.

Float drop: 1 9/16″

Choke Rod
Position fast idle tang on second step of fast idle cam and against shoulder of highest step, close the valve so that trip lever on choke shaft just contacts choke tang on lever and collar assembly. Check choke valve opening by inserting gauge of correct size between lower edge of valve and air horn wall. Adjust by bending tang on trip lever up or down as required. Setting: .190

Hold throttle valve wide open and move choke valve toward closed position until contact made at unloader tang. Check choke valve opening by inserting gauge of correct size between lower edge of valve and air horn wall. Adjust by bending unloader tang on throttle lever. Setting: .510″

Automatic Choke
This adjustment must be made with carburetors installed on engine. With choke valve completely closed, pull choke rod upward to end of travel. Bottom of rod should be even with top of hole in choke lever. Adjust by turning rod in or out as required. Careful – Rotate vertical section of rod, do not crank rod by turning offset portion.

Secondary Carburetor Lockout – Model H
Three separate adjustments required. Adjustment 3, must be made after all carburetors installed on engine.

1. With throttle valve closed and edge of throttle lever lockout tang flush with lockout lever, bend throttle lever tang as required to get a clearance of .020 between throttle lever tang and notch in lockout lever.

2. With throttle lever in locked out position, bend stop tang on lockout lever as required for clearance of .060 between stop tang and bottom surface of air horn.

3. This is a linkage adjustment and must be made with carburetors installed on engine and linkage connected. After linkage adjusted so that all carburetors operate simultaneously, insert a .250″ gauge between base of vacuum diaphragm and choke shaft actuating lever of primary carburetor, open choke valve until actuating lever contacts gauge. Bend tang on secondary carburetor so that it contacts choke shaft and fully opens choke valve. In this position, lockout lever should clear throttle lever tang.

Updated on 12/13/2020

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