1. Mercury 90 Hp 4 Stroke Service Manual

1965-1989 Service Manual Application: 2 hp To 40hp 2 Stroke 1 & 2 cylinder engines. A Typical Mercury-Mariner Service Manual Contains The Following Chapters: Subjects may differ depending on year/model. RELATED MERCURY - MARINER OUTBOARD SEARCHES: Carburetor Models: CARBURETOR Theory of Operations Prime Start System This carburetor assembly uses the PrimeStart system for precise fuel delivery during start-up, at all temperatures. Two electrothermal valves are installed on the carburetor assembly. The upper electrothermal valve controls fuel flow for carburetors #1 and #2, and the lower valve controls fuel flow for carburetors #3 and #4. Before start-up, the electrothermal ram (needle) is retracted (the fuel enrichment valve is opened) according to the temperature, allowing a high percentage of fuel to flow form the flat chamber into the venturi during start-up.

During start-up, the electrothermal ram (needle) is still retracted (the fuel enrichment valve is opened) according to the temperature, allowing a rich air/fuel mixture to be fed to the cylinders. After start-up, the current supplied form the electric power source and then flows to the electrothermal valves causing the wax in the valves to heat up. As the wax heats up the electrothermal ram (needle) begins to extend, partially closing the fuel enrichment valve, and reducing the flow of fuel from the float chamber into the venturi. After a few minutes, the electrothermal ram (needle) is fully extended, the fuel enrichment valve is fully closed, and enrichment ceases. A - Electrothermal Valve b - Fuel Enrichment Valve c - Electrothermal Ram (needle) d - Carburetor #1 and #3 e - Carburetor #2 and #4 Acceleration This carburetor assembly uses an accelerator pump to ensure that the proper amount of fuel reaches all of the carburetors during rapid throttle openings (preventing temporary lean conditions). As the throttle is opened, the throttle lever rotates and pushes the throttle lever link rod. The throttle lever link rod then pushes the diaphragm in the dashpot, forcing out the air.

The air flows through the in-line, one-way valve, and then to all of the carburetors. This additional air flows into the carburetors and mixes with the fuel from the main jets. This air/fuel mixture is then injected into the venturi, ensuring that enough fuel reaches the engine. As the throttle is closed, the throttle lever rotates back and the throttle lever link rod returns, causing the diaphragm in the dashpot to move back, As the diaphragm moves back, suction causes the air from the venturi of carburetor #4 to flow through a one-way valve in the carburetors and back to the dashpot. The in-line, one-way valve prevents the air in the hoses from flowing back to the dashpot. Also, the diaphragm functions as a coasting enrichener during quick deceleration, preventing the engine form stalling.

A - Throttle Lever b - Throttle Lever Link Rod c - Diaphragm d - Dashpot e - In-Line, One-Way Valve f - To Carburetor #1 g - To Carburetor #2 h - To Carburetor #3 i - Main Jet j - One-Way Valve Carburetor Adjustments Float Level 1. With carburetor turned upside down, and carb scale seated on inner edge, check float level from top of float to float bowl flange as shown. Adjust tab if out of specification. NOTE: Measure float level without gasket. NOTE: Bend tab to adjust float height. Idle Speed NOTE: Outboard should be completely warmed up for the idle speed adjustment. With the outboard in forward gear, adjust idle speed screw to obtain the specified idle speed.

NOTE: Turning idle speed adjustment screw; -clockwise will increase engine idling speed.counterclockwise will decrease engine idling speed. CYLINDER HEAD Adjustments Valve Clearance NOTE: Valve clearance adjustment should be made on a cold engine at room temperature.

Remove flywheel cover and spark plug cover. Disconnect spark plug leads and fuel hoses. A - Screw (2) M6 x 20 b - Flywheel Cover c - Screw (5) M6 x 16 d - Spark Plug Cover e - Fuel Hoses 3. Align timing marks on driven cams. NOTE: Use flywheel holder (91-83163M) to rotate flywheel and align timing marks.

Loosen timing belt tensioner bolt and remove tensioner spring. A - Timing Marks b - Timing Belt Tensioner Screw M10 x 45 c - Tensioner Spring 5. Remove timing belt and driven sprockets.

Remove cylinder head cover and spark plugs. A - Driven Sprocket Screw (2) M10 x 35 b - Washer (2) c - Driven Sprocket (2) d - Pin (2) e - Breather Hose f - Screw (14) M6 x 30 g - Cylinder Head Cover h - Rubber Gasket 7. Re-install driven sprockets and timing belt. NOTE: Make sure timing marks are still aligned. A - Pin (2) b - Washer (2) c - Driven Sprocket (2) d - Driven Sprocket Screw (2) M10 x 35 e - Timing Marks Aligned Driven Sprocket Screw Torque - 44 lb-ft (60 Nm) 8. Install tensioner spring and tighten timing belt tensioner.

A - Timing Belt Tensioner Screw M10 x 45 b - Tensioner Spring Timing Belt Tensioner Screw Torque - 29 lb-ft (40 Nm) 9. Measure intake and exhaust valve clearance using the Valve Clearance Measurement Steps below. VALVE CLEARANCE MEASUREMENT STEPS: a. Turn flywheel clockwise until cylinder #1’s piston is at TDC. Measure and record the intake valve clearance for cylinders #1 and #2. Measure and record the exhaust valve clearance for cylinders #1 and #3.

Turn the flywheel 360° clockwise. Measure and record the intake valve clearance for cylinders #3 and #4. Measure and record the exhaust valve clearance for cylinders #2 and #4. If adjustment of intake or exhaust valve clearance is necessary (out of specification) follow Changing Pad Thickness below. If no adjustment is necessary skip to step #11 on. CHANGING PAD THICKNESS 1. Align timing marks on driven cams.

Loosen timing belt tensioner and remove tensioner spring. NOTE: Do not mix valve train parts (valve pads, camshaft caps, camshafts).

Keep individual cylinder parts together. A - Timing Marks b - Timing Belt Tensioner Screw M10 x 45 c - Tensioner Spring 3. Remove timing belt and driven sprockets. Remove camshaft caps and camshafts. IMPORTANT: Remove camshaft cap bolts in reverse sequence (ex. A - Driven Sprocket Screw (2) M10 x 35 b - Washer (2) c - Driven Sprocket (2) d - Pin (2) e - Screw (4) M7 x 48 f - Screw (16) M7 x 37 g - Camshaft Cap - Top (2) h - Camshaft Cap (8) i - Oil Seal (2) j - Camshaft (2) 5. Carefully pry up the valve pad and remove it.

Measure and record (in the Measurement Table) the thickness of the removed valve pad with a micrometer. A - Valve Pad b - Screwdriver c - Measure Valve Pad Thickness With a Micrometer a. Select a proper replacement valve pad by calculating its thickness with the following formula. Removed Pad Thickness + Measured Valve Clearance – Specified Valve Clearance = New Pad Thickness NOTE: Measure the thickness of the new valve pads with a micrometer (thickness is not indicated on the pad). NOTE: Lubricate the valve pads with molybdenum disulfide before installing.

Mercury 90 Hp 4 Stroke Service Manual

Insert the proper valve pad into the valve lifter. Install camshafts and camshaft caps IMPORTANT: Install camshaft cap bolts in the proper sequence and torque.

A - Screw (4) M7 x 48 b - Camshaft Cap Top (2) c - Screw (16) M7 x 37 d - Camshaft Cap (8) e - Oil Seal (2) f - Camshaft - Intake g - Camshaft - Exhaust h - Pink Identification i - Exhaust Cam Tang 8. Install driven sprockets and timing belt.

Tighten timing belt tensioner and install tensioner spring. Re-check valve clearance using Valve Clearance Measurement Steps. NOTE: If any valve clearance is still out of specification, repeat all the valve clearance adjustment steps until the specified clearance is obtained. Loosen timing belt tensioner screw and remove tensioner spring. Remove driven sprockets and timing belt. Install cylinder head cover and driven sprockets. A - Rubber Gasket b - Cylinder Head Cover c - Screw (14) M6 x 30 d - Breather Hose e - Pin (2) f - Driven Sprocket (2) g - Washer (2) h - Driven Sprocket Screw (2) M10 x 35 Cylinder Head Cover Screw Torque - 70 lb-in.

(8 Nm) Driven Sprocket Screw Torque - 44 lb-ft (60 Nm) 14. Install timing belt and spark plugs. Install tensioner spring and tighten timing belt tensioner bolt.

Connect fuel hoses and spark plug leads. Install spark plug cover and flywheel cover. A - Fuel Hoses b - Spark Plug Cover c - Screw (5) M6 x 16 d - Flywheel Cover e - Screw (2) M6 x 20.