Mercury 300 350 (1271884 THRU 1448139) Parts & Diagrams

🔎 Mercury 300 350 Reference Library — Exploded parts diagrams (17 diagrams), specifications, common issues, and maintenance checklist.

The Mercury 300 350 is a 4-Stroke, V8 64-degree, DOHC, 32-valve outboard motor. Designed for large center-consoles, offshore sport-fishing boats, and multi-engine configurations.

Quick Reference Specifications

Specification	Value
Engine Type	4-Stroke, V8 64-degree, DOHC, 32-valve
Horsepower	300 HP
Displacement	4600 cc (4.6L / 279 CID)
Bore x Stroke	92 mm x 86 mm (3.62 in. x 3.38 in.)
Spark Plug (Type & Gap)	NGK LKAR7C-9
Engine Oil Capacity	7.0 L (7.4 qt)
Recommended Engine Oil	Mercury FourStroke Oil 25W-40
Gear Case Oil Capacity	970 mL (32.8 oz)
Idle Speed (in gear)	600 RPM
Full Throttle RPM Range	5200-6000
Fuel	Unleaded Gasoline, 87 Octane min.

Always verify specifications against your owner's manual for your specific serial number range.

Common Issues & Recommended Parts

Below are common maintenance scenarios for the Mercury 300 350:

Water Pump / Overheating: If the tell-tale stream is weak or absent, the water pump impeller likely needs replacement. Inspect annually or every 100 hours. → Recommended: Water Pump Impeller Kit
Engine Oil / Maintenance Light: 4-stroke engines require regular oil and filter changes. Use marine-grade oil rated for your engine. Change every 100 hours or annually. → Recommended: Oil Filter, Engine Oil
Fuel Injector Issues (EFI models): Rough idle or misfires may indicate clogged fuel injectors. Use fuel stabilizer and clean injectors periodically. → Recommended: Fuel Injector, Fuel Filter
Gear Case Oil Leak: Check lower unit seals if gear oil appears milky (water contamination). Replace seals and gaskets during lower unit service. → Recommended: Lower Unit Seal Kit, Drain Plug Gaskets
Anode Corrosion: Inspect sacrificial anodes regularly, especially in saltwater. Replace when 50% depleted to protect against galvanic corrosion. → Recommended: Zinc/Aluminum Anode Kit

Parts Diagrams & OEM Part Numbers

Expand the sections below to view detailed exploded parts diagrams and find the exact OEM replacement components for your Mercury 300 350.

▶BOTTOM COWL ASSEMBLY (47 parts)

Ref	OEM Part #	Part Name
-	37-23076	DECAL, MERCELECTRIC - BOTTOM COWL
--	13-20554	LOCKWASHER, ANCHOR BRACKET SCREW
1	103-1544A1	BOTTOM COWL ASSEMBLY
2	21041	INSERT, TAP LOCK
3	29206	PLUG, BOTTOM COWL HARNESS HOLE
4	10-45893	SCREW, PLUG TO BOTTOM COWL
5	13-26995	LOCKWASHER, PLUG FASTENING SCREW
6	11-26419	NUT, PLUG FASTENING SCREW
7	23760	BAFFLE, BOTTOM COWL
8	10-21106	SCREW, BAFFLE TO BOTTOM COWL
9	21104A2	CONNECTOR BASE ASSEMBLY
10	13-21972	LOCKWSHER, CONNECOTR BASE
11	11-21971	NUT, CONNECTOR BASE FASTENING
12	54-25231	CLIP, CONNECTOR BASE LEAD WIRE
13	10-21106	SCREW, LEAD WIRE CLIP TO BOTTOM COWL
14	29532	BRACKET, MAGNETO CONTROL (LOWER)
15	30612	LEVER, SHIFT CONTROL
16	23-29529	SLEEVE, MAGNETO BRACKET AND SHIFT LEVER
17	10-37612	SCREW, BRACKET AND LEVER FASTENING
18	12-8M0042641	WASHER, BRACKET AND LEVER FASTENING SCREW
19	17-30978A1	PIN ASSEMBLY, CLEVIS YOKE
20	17-239281	ROLL PIN, CLEVIS YOKE PIN
21	10-20584	SCREW, CLEVIS PIN FASTENING
22	13-29402	WASHER, WAVE - IN FASTENING SCREW
23	11-8M0204718	NUT, PIN FASTENING SCREW
24	25163	SHAFT, SHIFT (UPPER) - LONG SHAFT
25	27714	ROD (SLEEVE), SHIFT CONTROL END
26	11-25168	NUT, SHIFT SHAFT END ADJUSTING
27	25134	ROD, LINK - SHIFT SHAFT END
28	18-210711	COTTER PIN, LINK ROD TO SHIFT SHAFT
29	12-20583	WASHER, LINK ROD
30	24-25065	SPRING, DETENT
31	10-98256	SCREW, DETENT SPRING TO BOTTOM COWL
32	12-69057	WASHER, DETENT SPRING SCREW
33	11-8M0207775	NUT, DETENT SPRING SCREW
34	20557	BRACKET, CABLE END ANCHOR
35	10-29200	SCREW, ANCHOR BRACKET TO BOTTOM COWL
36	22-996642	ELBOW, PLASTIC - MAGNETO VENT TUBE
37	32-8M0108355	TUBE, VENT - MAGNETO
38	27-20390	GASKET, POWERHEAD TO BOTTOM COWL
39	30109	GROUND STRAP ASSEMBLY, CYLINDER BLOCK TO COWL
40	38-27720	PLATE, TRADE MARK - BOTTOM COWL
41	53-25539	FASTENER, PLATE TO BOTTOM COWL
42	26552	SUPPORT, EXTERNAL WIRING HARNESS
43	10-20639	SCREW, HARNESS SUPPORT TO BOTTOM COWL
44	12-20084	WASHER, HARNESS SUPPORT FASTENING SCREW
45	11-29250	NUT, HARNESS SUPPORT SCREW

▶CARBURETOR ASSEMBLY (38 parts)

Ref	OEM Part #	Part Name
--	10-22928	SCREW, KNOB FASTENING
1	1334-1701	CARBURETOR ASSEMBLY, COMPLETE (KB-2A) Comment: SERIAL 01324411-09999999
2	1395-8673	FLOAT ASSEMBLY
3	17-20853	PIN, FLOAT LEVER PINION
4	1399-102	LEVER, FLOAT (LOWER)
5	1399-101	LEVER, FLOAT (UPPER)
6	1395-92581	INLET NEEDLE, SEAT AND GASKET
7	27-25033	GASKET, INLET SEAT
8	1395-6027	SCREW, THROTTLE STOP LEVER
9	8146791	LEVER, THROTTLE STOP (SEE NOTE BELOW)
10	1399-1716	SHAFT, THROTTLE
11	24-26890	SPRING, THROTTLE SHAFT RETURN (LOWER CARBURETOR)
12	1399-1649	JET, MAIN FUEL (.049)
13	27-28409	GASKET, MAIN FUEL JET
14	24-27160	SPRING, IDLE ADJUSTMENT SCREW
15	1399-1713	SCRW, IDLE ADJUSTMENT
16	1399-99	GASKET, FLOAT BOWL COVER
17	1399-1133	COVER, FLOAT BOWL
18	1399-3938	SCREEN, FILTER-NOT AS SHOWN
19	10-22625	SCREW, FLOAT BOWL COVER (SHORT)
20	10-25850	SCREW, FLOAT BOWL COVER (LONG)
21	27-25851	GASKET, STRAINER COVER (LARGE)
22	27-25849	GASKET, STRAINER COVER (SMALL)
23	1399-1135	COVER, STRAINER
24	27-25848	GASKET, STRAINER COVER SCREW
25	10-25822	SCREW, STRAINER COVER FASTENING
26	1399-1715	NOZZLE, MAIN
27	10-23178	SCREW, PLUG-MAIN NOZZLE
28	10-23035	SCREW AND LOCKWASHER, THROTTLE SHUTTER
29	1399-107	SHUTTER, THROTTLE
30	1399-1714	TUBE, IDLE
31	27-23180	GASKET, IDLE TUBE
32	10-28845	SCREW, PLUG-BODY CHANNEL
33	19-20011	WELCH PLUG, BODY CHANNEL
34	10-28405	SCREW, PLUG-MAIN FUEL JET CHANNEL
35	27-28406	GASKET, BODY CHANNEL PLUG SCREW
36	27-20183	GASKET, CARBURETOR FLANGE
37	11-24652	NUT, CARBURETOR MOUNTING STUD

▶CARBURETOR LINKAGE AND CHOKE SOLENOID (43 parts)

Ref	OEM Part #	Part Name
--	12-20192	WASHER, CHOKE ROD SPRING SCREW
1	28936	CHOKE SOLENOID, TOP COWL
2	22647	DISCONNECT, KNIFE SPLICE - CHOKE SOLENOID
3	10-20540	SCREW, CHOKE SOLENOID TO TOP COWL
4	13-26992	LOCKWASHER, CHOKE SOLENOID SCREW
5	10-24773	SCREW, CHOKE SOLENOID TO TOP COWL
6	13-26991	LOCKWASHER, CHOKE SOLENOID SCREW
7	26716A1	GROUND STRAP ASSEMBLY, CHOKE SOLENOID TO ADAPTOR
8	32-61115	SLEEVE, CHOKE SOLENOID WIRE AND HARNESS WIRE
9	54-24836	CLAMP, CHOKE WIRE TO STARTER SOLENOID
10	27031A1	PLUNGER ASSEMBLY, CHOKE SOLENOID
11	27126	ADAPTOR PLATE, CHOKE PLUNGER
12	25-26633	GROMMET, ADAPTOR PLATE
13	10-21281	SCREW, ADAPTOR PLATE TO CHOKE ROD BRACKET
14	13-26994	LOCKWASHER, ADAPTOR PLATE FASTENING SCREW
15	12-26014	WASHER, CHOKE SOLENOID LINK
16	18-26953	COTTER PIN, CHOKE SOLENOID LINK FASTENING
17	1334-1701	CARBURETOR ASSEMBLY, COMPLETE Comment: SERIAL 01324411-09999999
18	27917	CLUSTER, THROTTLE LEVER (UPPER CARBURETOR) Comment: SERIAL 01324411-09999999
19	1395-6027	SCREW, SET - CLUSTER TO THROTTLE LEVER
20	10-20176	SCREW, CHOKE LEVER PIVOT PIN
21	30014	SHUTTER, CHOKE Comment: SERIAL 01324411-09999999
22	24-26067	SPRING, CHOKE SHUTTER
23	26645A1	CHOKE LEVER ASSEMBLY (UPPER CARBURETOR)
24	23-26888	BUSHING, CHOKE LEVER
25	18-210711	COTTPER PIN, CHOKE LEVER RETAINING
26	27870	CLAMP, THROTTLE PICKUP BRACKET
27	10-69022	SCREW, CLAMP TO THROTTLE PICKUP BRACKET
28	28007A3	BRACKET, THROTTLE PICKUP Comment: SERIAL 01324411-09999999
29	10-29239	SCREW, THROTTLE BRACKET MOUNTING
30	12-20192	WASHER, THROTTLE BRACKET SCREW
31	10-20650	SCREW, CHOKE ROD SPRING MOUNTING
32	24-26068	SPRING, CHOKE ROD TO RETAINER
33	27711	RETAINER, CHOKE ROD SPRING
34	10-28713	SCREW, RETAINER TO LOWER CARBURETOR
35	90242A1	KNOB, CHOKE ROD
36	25-20116	GROMMET, CHOKE ROD
37	22462	"U" LINK, CHOKE KNOB TO CHOKE ROD
38	10-69022	SCREW, "U" LINK TO CHOKE KNOB
39	13-26996	LOCKWASHER, "U" LINK FASTENING SCREW
40	18-210711	COTTPER PIN, CHOKE LEVER AND ROD FASTENING
41	28978	CHOKE ROD
42	17-25391	RIVET, CHOKE ROD TO CHOKE LEVER

▶CLAMP AND SWIVEL BRACKET (40 parts)

Ref	OEM Part #	Part Name
-	54-25735	CLIP, SAFETY CHAIN (NO LONGER USED ON LATER ENGINES)
--	12-27964	WSHER, SWIVEL PIN TO BOTTOM YOKE (.018)
1	1440-1464A1	CLAMP BRACKET ASSEMBLEY (LONG SHAFT)
2	28403A3	THUMB SCREW ASSEMBLY (LONG SHAFT)
3	12-28404	WASHER, THUMB SCREW (LONG SHAFT)
4	28122	TUBE, TILT - CLAMP BRACKET TO SWIVEL BRACKET
5	15-25600	SHIM, CLAMP BRACKET TO SWIVEL BRACKET (.010)
6	11-8M2014641	NUT, TILT TUBE
7	25606	CAP, PLASTIC - TILT TUBE
8	16-59625	STUD, CLAMP BRACKET
9	23-59624	SPACER, CLAMP BRACKET STUD
10	13-8M0204647	LOCKWASHER, CLAMP BRACKET STUD
11	11-22053	NUT, CLAMP BRACKET STUD
12	17-8M0026068	TILT LOCK PIN ASSEMBLY
13	26903A3	REVERSE LOCK ASSEMBLY (LONG SHAFT)
14	18-45882	COTTER PIN, REVERSE LOCK TO SHAFT
15	24-29821	SPRING, REVERSE LOCK TENSION
16	17-25598	ROLL PIN, REVERSE LOCK SPRING ATTACHING
17	56349	SHAFT, REVERSE LOCK TO SWIVEL BRACKET
18	1442-1400A1	SWIVEL BRACKET ASSEMBLY (LONG SHAFT)
19	22-69059	FITTING, GREASE - SWIVEL BRACKET
20	26-32911	OIL SEAL, SWIVEL BRACKET
21	19-77633Q	LUBRICAP, SWIVEL BRACKET GREASE FITTING
22	29057	LEVER, TILT STOP - PORT SIDE (LONG SHAFT)
23	10-27791	SCREW, ANCHOR - TILT STOP LEVER (LONG SHAFT
24	23-29055	SPACER, TILT STOP LEVER (LONG SHAFT)
25	10-27790	SCREW, RETAINING - TILT STOP LEVER (LONG SHAFT)
26	15-20473	SHIM, RETAINING SCREW - PORT SIDE
27	13-20846	WASHER, WAVE - RETAINING SCREW - PORT SIDE
28	11-24652	NUT, ANCHOR AND RETAINING SCREW (.060)
29	12-25176	WASHER, SWIVEL PIN TO BOTTOM YOKE
30	30462A1	BOTTOM YOKE ASSEMBLY (LONG SHAFT)
31	17-28419A4	SWIVEL PIN AND TOP YOKE ASSEMBLY (LONG SHAFT)
32	11-71956	NUT, SWIVEL PIN (LONG SHAFT) - NOT AS SHOWN
33	30711	BUMPER, TOP YOKE
34	38-31056	SERIAL PLATE
35	10-25612	SCREW, DRIVE - SERIAL PLATE TO SWIVEL BRACKET
36	10-68298	BOLT, CARRIAGE - CLAMP BRACKET TO BOAT TRANSOM (LONG SHAFT)
37	12-68410	WASHER, CARRIAGE BOLT (LONG SHAFT)
38	11-82670912	NUT, CARRIAGE BOLT (LONG SHAFT)

▶COWLING AND FRONT COVER (18 parts)

Ref	OEM Part #	Part Name
--	92-271091	ADHESIVE COMPOUND (3 1/2 OUNCE KIT) EMBLEM FASTENING
1	2104-2654A5	COWL FRONT COVER ASSEMBLY
2	26183A5	EMBLEM, FRONT COVER (SEE NOTE BELOW)
3	10-29552	SCREW, COVER FASTENING
4	12-26162	WASHER, COVER FASTENING SCREW
5	12-27897	WASHER, COVER FASTENING SCREW
6	20721	BUMPER, RUBBER-FRONT COVER (SMALL)
7	269011	BUMPER, RUBBER-FRONT COVER (LARGE)
8	28999	BLANKET, SOUND ABSORBING-FRONT COVER
9	12-29000	WASHER, BLANKET TO FRONT COVER
10	11-28968	NUT, SPEED-SOUND BLANKET FASTENING
11	190-1819A2	WRAP AROUND COWL ASSEMBLY
12	21060	HANDLE, COWL LATCH
13	53-21058	"E" RING, COWL LATCH HINGE PIN
14	17-21057	PIN, HINGE-COWL LATCH HANDLE
15	25690	SWIVEL, COWL LATCH
16	25691	HOOK, COWL LATCH FASTENING
17	24825	BLANKET, WRAP AROUND COWL

▶CRANKSHAFT, PISTON AND CONNECTING ROD (24 parts)

Ref	OEM Part #	Part Name
-	11-24652	NUT, MAIN BEARING CLAMPING SCREW Comment: ALUMINUM
--	39-20992A12	RING, PISTON (.015 OVERSIZE)
1	400-2976A2	CRANKSHAFT
2	25-29619	"O"RING, DRIVE SHAFT SPLINE
3	500-5345A4	CENTER MAIN BEARING ASSEMBLY
4	10-28666	SCREW, CENTER MAIN BEARING CLAMPING
5	29-20046T	BEARING, NEEDLE
6	20047	RACE, OUTER
7	53-20048	RING, SNAP - OUTER RACE CLAMPING
8	527-1619A4	MAIN BEARING ASSEMBLY (VALVE TYPE) Comment: ALUMINUM
9	10-26184	SCREW, MAIN BEARING CLAMPING Comment: ALUMINUM
10	34-88498A1	REED SET, MATCHED - MAIN BEARING Comment: ALUMINUM
11	34-20053	REED STOP, MAIN BEARING REED VALVES Comment: ALUMINUM
12	12-26014	WASHER, REED STOP MOUNTING SCREW Comment: BRONZE - NO LONGER AVAILABLE, ORDER A-527-1619A1
13	10-77280	SCREW, REED STOP MOUNTING Comment: ALUMINUM
14	726-1611A2	PISTON AND PISTON PIN ASSEMBLY
15	40-20057	LOCK RING, PISTON PIN
16	39-20058	RING, PISTON
17	600-2748A3	CONNECTING ROD AND CAP ASSEMBLY (SEE NOTE BELOW)
18	10-45379	SCREW, CONNECTING ROD
19	11-20061	NUT, CONNECTING ROD SCREW
20	29-20046T	BEARING, NEEDLE - CRANKPIN
21	29-20063	BEARING, NEEDLE - PISTON PIN
22	12-20064	WASHER, NEEDLE LOCATING

▶CYLINDER BLOCK AND CRANKCASE ASSEMBLY (46 parts)

Ref	OEM Part #	Part Name
-	17-20032	DOWEL PIN, CYLINDER BLOCK TO MAIN BEARING
--	12-20028	WASHER, TRANSFER PORT COVER FASTENING SCREW
1	808-1321A4	CYLINDER BLOCK AND CRANKCASE ASSEMBLY
2	23-26348	BUSHING, CRANKCASE
3	22-996642	STUD, CARBURETOR MOUNTING (1-1/4")
4	17-43044	DOWEL PIN, CRANKCASE TO CYLINDER BLOCK
5	16-33111	STUD, CRANKCASE TO DRIVE SHAFT HOUSING (1-9/16")
6	16-8M0034463	STUD, CYLINDER BLOCK TO DRIVE SHAFT HOUSING (3-3/8")
7	16-29989	STUD, SYLINDER BLOCK TO DRIVE SHAFT HOUSING (1-7/8")
8	22-328022	PLUG, PIPE - WATER PRESSURE HOLE (SEE NOTE BELOW)
9	10-22039	SCREW, CRANKCASE TO CYLINDER BLOCK (2-3/4")
10	10-78841	SCREW, CRANKCASE TO CYLINDR BLOCK (1-1/2")
11	11-29250	NUT, CRANKCASE FASTENING SCREW
12	10-98260	SCREW, MAIN BEARING LOCKING Comment: SERIAL 01352948-09999999
13	14-20091	TAB WASHER, BEARING LOCKING SCREW
14	10-20359	SCREW, CENTER MAIN BEARING LOCKING
15	1100-339A1	END CAP ASSEMBLY, UPPER
16	30-63742T	BEARING, BALL - UPPER END CAP
17	25-20081	"O" RING, UPPER END CAP
18	26-41953	OIL SEAL
19	15-20082A1	SHIM, UPPER END CAP TO CRANKCASE
20	10-29198	SCREW, UPPER END CAP MOUNTING
21	1102-4181A3	END CAP ASSEMBLY, LOWER
22	30-63742T	BEARING, BALL - LOWER END CAP
23	25-20081	"O" RING, LOWER END CAP
24	26-29477	OIL SEAL, LOWER
25	15-20085A1	SHIM, LOWER END CAP TO CRANKCASE
26	10-29198	SCREW, LOWER END CAP MOUNTING
27	27-26923	GASKET, MANIFOLD PLATE TO COVER
28	26922	PLATE, EHAUST MANIFOLD
29	28240	COVER, EXHAUST MANIFOLD
30	10-28666	SCREW, MANIFOLD COVER AND HIGH TENSION LEAD CLIP MOUNTING
31	12-20028	WASHER, MANIFOLD COVER AND HIGH TENSION LEAD CLIP SCREWS
32	1000-1A1	CYLINDER BLOCK COVER ASSEMBLY (SEE NOTE BELOW)
33	23-26348	BUSHING, CYLINDER BLCOK COVER
34	27-22333	GASKET, CYLINDER BLOCK COVER
35	10-20653	SCREW, CYLINDER BLOCK COVER MOUNTING
36	11-24652	NUT, COVER MOUNTING SCREW
37	27-279361	GASKET, TRANSFER PORT COVER
38	27935	COVER, TRANSFER PORT
39	10-20540	SCREW, TRANSFER PORT COVER FASTENING
40	22-62365A1	CHECK VALVE ASSEMBLY, BLEED HOSE (UPPER)
41	21-28481A1	CHECK VALVE ASSEMBLY, BLEED HOSE
42	32-9912688	HOSE, CYLINDER BLEED (6-1/2")
43	22-67902	CONNECTOR, CYLINDER BLEED HOSE (LOWER)
44	54-20387	CLAMP, BLEED HOSE TO CHECK VALVE AND CONNECTOR

▶DRIVE SHAFT HOUSING ASSEMBLY (42 parts)

Ref	OEM Part #	Part Name
--	12-20084	WASHER, LOWER MOUNT COVER SCREW
1	1535-1566	DRIVE SHAFT HOUSING (USE WITH 7/16" STUD) - LONG SHAFT Comment: SERIAL 01260217-09999999
2	32-25076	TUBE, WATER INLET (LONG SHAFT)
3	25-24961	RING, RUBBER - WATER INLET TUBE
4	26-25192	SEAL, WATER INLET TUBE
5	23-23651	SLEEVE, WATER INLET TUBE
6	27898	BAFFLE, EXHAUST RELIEF (LONG SHAFT)
7	10-25255	SCREW, BAFFLE TO DRIVE SHAFT HOUSING
8	27-24899	GASKET, DRIVE SHAFT HOUSING TO BOTTOM COWL
9	32445A1	NUT, POWERHEAD STUDS
10	10-25093	SCREW, GEAR HOUSING TO DRIVE SHAFT HOUSING
11	16-29103	STUD, DRIVE SHAFT HOUSING TO GEAR HOUSING (7/16")
12	11-8M0204653	NUT, GEAR HOUSING AND DRIVE SHAFT HOUSING STUDS (7/16")
13	28593	ROD, PUSH - REVERSE LOCK (LONG SHAFT)
14	17-24887	PIN, REVERSE LOCK LEVER
15	18-25191	COTTER PIN, PUSH ROD
16	24-25122	SPRING, TENSION - PUSH ROD
17	52920	LEVER, REVERSE LOCK
18	24926A1	UPPER MOUNT ASSEMBLY, UPPER
19	79680A1	COVER, UPPER MOUNT - OUTSIDE HALF
20	79680A1	COVER, UPPER MOUNT - INSIDE HALF
21	24929	PACKING, "U" CUP
22	12-24889	WASHER, UPPER MOUNT STUD (17/32" I.D.)
23	12-24891	WASHER, RUBBER - UPPER MOUNT STUD
24	23-30474	SPACER, UPPER MOUNT STUD
25	12-11367	WASHER, UPPER MOUNT STUD (25/64" I.D.)
26	11-23161	NUT, UPPER MOUNT STUD
27	25305	CAP, RUBBER - UPPER MOUNT
28	10-28772	SCREW, UPPER MOUNT COVER (1-1/2")
29	10-29389	SCREW, UPPER MOUNT COVER (1-7/8")
30	12-8M0204649	WASHER, MOUNTING COVER SCREW
31	11-35888	NUT, MOUNTING COVER SCRW
32	75304T1	MOUNT, RUBBER - LOWER
33	12-28053	WASHER, RUBBER - LOWER MOUNT
34	12-28051	WASHER, LOWER MOUNT
35	12-30119	WASHER, MOUNTING SCREW (1/8") Comment: USE WITH A-30202A1 BOTTOM YOKE
36	11-25096	NUT, MOUNTING SCREW
37	10-24874	SCREW, LOWER MOUNT (5-1/2")
38	25067	BUMPER, RUBBER - MOUNTINS SCREW
39	28242	COVER, LOWER MOUNT (STARBOARD SIDE)
40	10-29256	SCREW, LOWER MOUNT COVER FASTENING
41	22-390721	PLUG, GREASE - REVERSE LOCK HOLE

▶FLYWHEEL ASSEMBLY AND STATOR (16 parts)

Ref	OEM Part #	Part Name
-	12-26907	WASHER, RATCHET TO FLYWHEEL (1/8" SPACER)
1	11-8M0214915	NUT, FLYWHEEL
2	12-26617	WASHER, FLYWHEEL NUT
3	20455A2	KEY, FLYWHEEL
4	215-3289A1	FLYWHEEL ASSEMBLY (WITHOUT SPACERS) SEE NOTE #1 BELOW
5	22823	PULLEY, FLYWHEEL SEE NOTE #2 BELOW
6	12-25293	WASHER, PULLEY TO FLYWHEEL SEE NOTE #2 BELOW
7	17-26618	DOWEL PIN, FLYWHEEL PULLEY
8	50-25263	RATCHET, FLYWHEEL
9	10-29238	CSREW, RATCHET TO FLYWHEEL
10	398-1455	STATOR, ALTERNATOR-FLYWHEEL
11	22647	DISCONNECT, KNIFE SPLICE-STATOR LEAD WIRE
12	32-61115	SLEEVE, RUBBER-STATOR LEAD WIRE
13	10-68918	SCREW, STATOR TO UPPER END CAP
14	54-24836	CLIP, STATOR LEAD TO CRANKCASE FLANGE
15	10-8M0113176	SCREW, STATOR LEAD CLIP FASTENING

▶FUEL PUMP ASSEMBLY (30 parts)

Ref	OEM Part #	Part Name
-	22-390721	PLUG, PIPE - FUEL PUMP
--	22-22948	NUT, FILTER TEE
1	30269A2	FUEL PUMP ASSEMBLY
2	27-23005	GASKET, CHECK VALVE TO HOUSING
3	21-8M0082362	VALVE, CHECK
4	23004	RETAINER, CHECK VALVE
5	10-43725	SCREW, RETAINER TO HOUSING
6	27-24863	GASKET, FUEL PUMP
7	23014	DIAPHRAGM, FUEL PUMP
8	23008	COVER, FUEL PUMP
9	27-30276	GASKET, FUEL PUMP COVER
10	10-29126	SCREW, FUEL PUMP MOUNTING (1-3/4") Comment: SERIAL 01261035-09999999
11	10-29029	SCREW, FUEL PUMP MOUNTING (1-1/2")
12	22-22993	CONNECTOR, FUEL LINE TO FUEL PUMP INLET
13	22-22946	SLEEVE, RUBBER
14	22-22948	NUT, ELBOW
15	32-30035	FUEL LINE, FUEL PUMP TO LOWER FILTER
16	22-22995	ELBOW, FUEL PUMP OUTLET TO FUEL LINE
17	22-22946	SLEEVE, RUBBER
18	22-22948	NUT, ELBOW
19	32-30036	FUEL LINE, FUEL PUMP TO ADAPTOR
20	22833	ADAPTOR, CHECK UNIT (FUEL LINE)
21	23069	STEM, CHECK UNIT ADAPTOR
22	25-16524	"O" RING, ADAPTOR STEM
23	24-23067T	SPRING, ADAPTOR STEM
24	30188	CUP WASHER, ADAPTOR
25	10-20784	SCREW, ADAPTOR TO BOTTOM COWL
26	11-24652	NUT, ADAPTOR SCREW
27	32-30040	FUEL LINE, UPPER TO LOWER FILTER
28	22-25956	TEE ASSEMBLY, LOWER FILTER Comment: SERIAL 01261035-09999999

▶GEAR HOUSING ASSEMBLY (PAGE 1) (32 parts)

Ref	OEM Part #	Part Name
-	27-31367	GASKET, WATER INTAKE SCREEN TO GEAR HOUSING
1	1603-1868A4	GEAR HOUSING ASSEMBLY (7/16" STUD) Comment: SERIAL 01231090-09999999
2	16-8M0133358	STUD, GEAR HOUSING TO DRIVE SHAFT HOUSING (7/16" X 2") Comment: SERIAL 01231090-09999999
3	31-62091T	BEARING, ROLLER - DRIVE SHAFT
4	32-23652	TUBE, WATER INLET - LOWER
5	23-23651	SLEEVE, WATER INLET TUBE
6	26-20232	SEAL, WATER TUBE
7	35-23654	SCREEN, WATER INTAKE - GEAR HOUSING
8	45-29618A1	DRIVE SHAFT ASSEMBLY ( LONG SHAFT)
9	53-29115	RING, RETAINING - BALL BEARING (3/4" I.D.) - SEE NOTE
10	43-20834	GEAR, PINION
11	14-29163	TAB WASHER, PINION GEAR SCREW
12	10-20925	SCREW, PINION GEAR RETAINING
13	15-20929A1	SHIM, BALL BEARING TO DRIVE SHAFT
14	30-72961	BEARING, BALL - DRIVE SHAFT
15	25-26722	"O" RING, WATER PUMP CARTRIDGE
16	46-29117A1	WATER PUMP CARTRIDGE ASSEMBLY
17	26-90562	OIL SEAL
18	28091	INSER, WATER UMP CARTRIDGE
19	28-28657	KEY, WATER PUMP CARTRIDGE
20	47-89983T	IMPELLER, WATER PUMP
21	28-8M0032837	PIN, IMPELLER DRIVE
22	20272	PLATE, OUTLET - WATER PUMP COVER
23	20270A2	WATER PUMP COVER ASSEMBLY
24	26-23517	OIL SEAL
25	25-20273	RING, RUBBER - CENTRIFUGAL SLINGER
26	25-29619	"O" RING, DRIVE SHAFT - UPPER
27	25136	SHAFT, SHIF - LOWER
28	53-29641	CLIP, RETAINING - SHIFT SHAFT
29	23-46284A1	BUSHING ASSEMBLY, SHIF SHAFT
30	26-892361	OIL SEAL (SPRING LOADED)
31	25-25439	"O" RING, SHIFT SHAFT BUSHING

▶GEAR HOUSING ASSEMBLY (PAGE 2) (33 parts)

Ref	OEM Part #	Part Name
--	48-29296A2	PROPELLER ASSEMBLY (2 BLADE - ALUMINUM)
32	52918	CAM, LOWER REVERSE LOCKING
33	52919	CAM UPPER REVERSE LOCKING
34	12-191833	WASHER, GREASE FILLER AND FLUSHING HOLE SCREW
35	10-79953Q04	SCREW, GREASE FILLER AND FLUSHING HOLE
36	19643	WASHER, GEAR HOUSING VENT SCREW
37	10-28653	SCREW, GEAR HOUSING VENT
38	760394	CAM, SHIFT
39	20930	FOLLOWER, CAM
40	20843	SLIDE, CROSS PIN
41	24-20254	SPRING, CAM FOLLOWER PIN
42	15-20928A1	SHIM, BALL BEARING TO GEAR HOUSING
43	30-20840	BEARING, BALL - FORWARD GEAR
44	43-20975A5	FORWARD GEAR ASSEMBLY
45	31-20249	BEARING, ROLLER - FORWARD GEAR
46	52-32189	RATCHET, SLIDING CLUTCH
47	17-20841	PIN, CROSS - RATCHET TO PROPELLER SHAFT
48	53-20842	RING, RETAINING - CROSS PIN
49	44-25254	SHAFT, PROPELLER
50	43-20975A5	REVERSE GEAR ASSEMBLY
51	20864	RING, ADAPTOR - BALL BEARING
52	30-20839T	BEARING, BALL - REVERSE GEAR
53	15-20927A1	SHIM, ADAPTOR RING TO GEAR HOUSING
54	25-20863	"O" RING, BEARING CARRIER
55	20862A1	BEARING CARRIER ASSEMBLY
56	31-20249	BEARING, ROLLER
57	26-90562	OIL SEAL
58	12-22970	WASHER, GEAR HOUSING COVER
59	20865	COVER, GEAR HOUSING
60	12-25251	WASHER, BACKING (1/8")
61	12-25252	WASHER, BACING (1/32")
62	14-25250	TAB WASHER, PROPELLER NUT
63	11-29825	NUT, PROPELLER (NYLON)

▶MAGNETO ADAPTOR AND PILOT ASSEMBLY (66 parts)

Ref	OEM Part #	Part Name
-	29321A7	MAGNETO ADAPTOR AND PILOT ASSEMBLY, COMPLETE
--	12-20533	WASHER, MAGNETO STOP FASTENING SCREW Comment: SERIAL 00000000-01231089
1	394-2271A2	MAGNETO ASSEMBLY, COMPLETE
2	45-27951	SHAFT, MAGNETO DRIVE
3	39560A1	MAGNETO PILOT ASSEMBLY Comment: SERIAL 01231090-09999999
4	30-20066	BEARING, BALL-MAGNETO PILOT
5	24-27944	SPRING, HORSESHOE-MAGNETO PILOT
6	17-27962	PIN, ANCHOR-AHORSESHOE SPRING TO PILOT
7	12-8M0204649	WASHER, HORSESHOE SPRING TO ANCHOR PIN
8	27946A1	ECONOMIZER COLLAR AND PIN ASSEMBLY
9	17-27961	PIN, ECONOMIZER COLLAR-SPRING RETAINER
10	22-25094	FITTING, GREASE-ECONOMIZER COLLAR
11	38230A1	THROTTLE ACTUATOR ASSEMBLY
12	23-26602	BUSHING, NYLON-THROTTLE ACTUATOR
13	10-20665	SCREW, THROTTLE ACTUATOR TO ECONOMIZER COLLAR
14	12-847883	WASHER, THROTTLE ACTUATOR SCREW
15	27947	SWIVEL, LINKAGE-ECONOMIZER COLLAR
16	25996A1	SWIVEL AND LINK ROD ASSEMBLY
17	66856A1	ADAPTOR, MAGNETO
18	22-25094	FITTING, GREASE-MAGNETO ADAPTOR
19	12-27939	WASHER, MAGNETO PILOT
21	13-27959	WASHER, WAVE-MAGNETO BALL BEARING TENSION
22	27955	CAP, MAGNETO ADAPTOR AND PILOT FASTENING
23	10-30110	SCREW, ADAPTOR AND PILOT TO MANGETO
24	10-78841	SCREW, ADAPTOR AND PILOT TO CRANKCASE
25	12-20084	WASHER, ADAPTOR AND PILOT TO CRANKCASE SCREW
26	11-22053	NUT, ADAPTOR AND PILOT TO CRANKCASE SCREW
27	53458	PLATE, THROTTLE STOP Comment: SERIAL 01231090-09999999
28	37-29315	DECAL, THROTTLE STOP PLATE Comment: SERIAL 01231090-09999999
29	10-24933	SCREW, THROTTLE STOP ADJUSTING Comment: 2 EACH REQUIRED WITH A-27943 PLATE
30	11-20088	NUT, THROTTLE STOP ADJUSTING SCREW Comment: 2 EACH REQUIRED WITH A-27943 PLATE
31	26852	CAP, NYLON-ADJUSTING SCREW Comment: 2 EACH REQUIRED WITH A-27943 PLATE
32	10-69035	SCREW, THROTTLE STOP PLATE TO ADAPTOR
33	28-28657	KEY, MAGNETO DRIVING
34	23-27957	SPACER, PULLEY TO MAGNETO ADAPTOR CAP - OLD STYLE
35	29783A2	PULLEY, DRIVEN - OLD STYLE
36	20136	FLANGE, DRIVEN PULLEY - OLD STYLE
37	29784	HUB, DRIVEN PULLEY - NEW STYLE-SEE NOTE BELOW
38	29783A1	DRIVEN PULLEY ASSEMBLY - NEW STYLE-SEE NOTE BELOW
39	17-24873	ROLL PIN, FLANGE LOCATING - NEW STYLE-SEE NOTE BELOW
40	29785	FLANGE, DRIVEN PULLEY - NEW STYLE-SEE NOTE BELOW
41	12-20138	WASHER, PULLEY CLAMPING SCREW
42	10-32228	SCREW, PULLEY CLAMPING
43	20140	BELT, TIMING
44	27949	ROD, LIN-UPPER
45	11-25168	NUT, UPPER LINK ROD ADJUSTING
46	27948	SWIVEL, UPPER AND LOWER LIND RODS
47	28061	LEVER, LINKAGE-UPPER
48	27941	LEVER, LINKAGE-LOWER
49	27950	ROD, LIN-LOWER
50	27940	SHAFT, VERTICAL
51	23-22981	BUSHING, NYLON-VERTICAL SHAFT
52	17-25870	ROLL PIN, VERTICAL SHAFT AND LINKAGE LEVERS
53	12-8M0204649	WASHER, UPPER AND LOWER SWIVEL
54	11-8267089	NUT, UPPER AND LOWER SWIVEL TO LEVER AND BRACKET
55	10-25781	SCREW, SET-LINKAGE LEVER
56	12-25866	WASHER, VERTICAL SHAFT-CENTER
57	33-813416	SPARK PLUG
58	85-63709A1	PROTECTOR, SPARK PLUG
59	84-821945A46	CABLE, HIGH TENSION LEAD-SPARK PLUG
60	25-25429	"O" RING, HIGH TENSION LEAD CABLE TO END CAP COVER
61	54-20534	CLIP, HIGH TENSION LEAD CABLE FASTENING
62	54-25231	CLIP, MERCURY SWITCH AND HARNESS LEADS
63	10-20401	SCREW, LEAD CLIP TO MAGNETO
64	8M0084613	"D" WASHER, CLIP FASTENING SCREW
65	394-1134A1	GROUND STRAP ASSEMBLY, MAGNETO TO CRANKCASE

▶MAGNETO ASSEMBLY (INTERNAL PARTS) (47 parts)

Ref	OEM Part #	Part Name
-	394-2271A2	MAGNETO ASSEMBLY, COMPLETE (4 D-3) SEE NOTE BELOW
--	10-25509	SCREW AND LOCKWASHER, BRACKET LOCKING
1	394-1570	FRAME, MAGNETO HOUSING
2	10-25510	SCREW, SET-COIL BRIDGE
3	394-1051	LOCKWIRE, COIL BRIDGE SET SCREW
4	30-24998	BEARING, BALL (DRIVE END)
5	394-1067A1	MAGNETO ROTOR AND SHAFT
6	30-49090	BEARING, BALL (OPPOSITE DRIVE END)
7	394-1637	SUPPORT, BALL BEARING
8	10-25509	SCREW AND LOCKWASHER, SUPPORT TO FRAME
9	84-60466A13	WIRE ASSEMBLY, PRIMARY GROUND LEAD
10	10,10-29182	SCREW, PRIMARY GROUND
11	394-1579	INSULATOR, PRIMARY GROUND TERMINAL
12	12-29099	WASHER, INSULATING-PRIMARY GROUND SCREW
13	23-62769	BUSHING, INSULATING-HOUSING FRAME
14	12-26014	WASHER, PRIMARY GROUND SCREW
15	11-24656	NUT, LOCK-PRIMARY GROUND SCREW
16	11-68219	NUT, PRIMARY GROUND SCREW
17	394-1128A1	COIL ASSEMBLY
18	394-1050	CLIP, COIL-HIGH TENSION
19	13-23836	LOCKWASHER, COIL TERMINAL
20	394-1131	NUT, COIL CLIP FASTENING
21	393-1504A11	BREAKER ASSEMBLY
22	393-1586	GROMMET, PLASTIC-BREAKER BRACKET
23	16-29230	STUD, PRIMARY LEAD AND TENSION SPRING FASTENING
24	11-29236	NUT, PRIMARY LEAD FASTENING
25	394-1106A1	HOLDER AND CAM WICK ASSEMBLY
26	12-26439	WASHER, BREAKER PIVOT PIN
27	18-26953	COTTPER PIN, BREAKER TO PIVOT PIN
28	10-20597	SCREW, BREAKER HOLDER TO HOUSING
29	394-1130A1	CONDENSER
30	10-25509	SCREW AND LOCKWASHER, CONDENSER FASTENING
31	27-29166	GASKET, MAGNETO COVER
32	394-1577A2	COVER, MAGNETO
33	10-29418	SCREW, COVER TO FRAME
34	14-38359	TAB WASHER, COVER FASTENING SCREW
35	394-2602A1	MAGNETO ROTOR ASSEMBLY
36	394-1110	CLIP, SPRING
37	27-25725	GASKET, END CAP COVER
38	394-1561A2	END CAP COVER ASSEMBLY
39	394-1065A1	LEAD ASSEMBLY, HIGH TENSION
40	394-1056A1	BRUSH AND SPRING ASSEMBLY
41	10-25517	SCREW, HIGH TENSION CABLE FASTENING
42	29121	PIPE PLUG, END CAP COVER
43	10-29418	SCREW, END CAP COVER TO MAGNETO COVER
44	14-38359	TAB WASHER, COVER FASTENING SCREW
45	22-996642	ELBOW, PLASTIC-MAGNETO COVER VENT

▶MISCELLANEOUS PARTS/ACCESSORIES (1 parts)

Ref	OEM Part #	Part Name
-	90-45772	MARK 35A, MERC 300, MERC 350 PARTS LIST

▶RECTIFIER, STARTER SOLENOID AND WIRING HARNESS (26 parts)

Ref	OEM Part #	Part Name
--	13-26992	LOCKWASHER, SOLENOID FATENING SCREW
1	32177A2	RECTIFIER ASSEMBLY
2	32-26693A1	SLEEVE, RECTIFIER LEAD (RED)
3	22647	DISCONNECT, KNIFE SPLICE - RECTIFIER LEAD WIRES
4	13-8M0204647	LOCKWASHER, RECTIFIER MOUNTING SCREW
5	11-21929	NUT, RECTIFIER MOUNTING SCREW
6	28597	BRACKET, RECTIFIER MOUNTING
7	10-21091	SCREW, RECTIFIER BRACKET TO BOTTOM COWL
8	11-24652	NUT, BRACKET MOUNTING SCREW
9	54-24836	CLAMP, LEAD WIRE TO RECTIFIER BRACKET - UPPER (1/4")
10	54-22740	CLAMP, LEAD WIRE TO RECTIFIER BRACKET - LOWER (3/8")
11	10-8M0113176	SCREW, LEAD WIRE CLAMP TO BRACKET
12	8M0084613	"D" WASHER, CLAMP FASTENING SCREW
13	32445A1	SOLENOID, STARTER
14	28016A1	GROUND STRAP ASSEMBLY, SOLENOID TO STARTER
15	84-93389A12	WIRE, STRTER TO STARTER SOLENOID
16	13-8M0204647	LOCKWASHER, SOLENOID TERMINAL (5/16")
17	11-26062	NUT, CAP - SOLENOID TERMINAL - OUTSIDE (5/16")
18	10,13-26996	LOCKWASHER, SOLENOID TERMINAL
19	10,11-68219	NUT, SOLENOID TERMINAL
20	10-29238	SCREW, SOLENOID TO STARTER MOTOR
21	33401	WIRING HARNESS (INTERNAL)
22	24-28975	SPRING, GARTER - INTERNAL WIRING HARNESS
23	26079A2	PLATE, BACKING - WIRING HARNESS
24	10-45893	SCREW, BACKING PLATE TO BOTTOM COWL
25	54-22783	"S" CLIP, WIRING HARNESS LEADS TO BOTTOM COWL

▶TOP COWL AND STARTER ASSEMBLY (36 parts)

Ref	OEM Part #	Part Name
--	11-28968	NUT, SPEED-VENT SCREEN TO TOP COWL - SEE NOTE #1 BELOW
1	177-1600A2	TOP COWL ASSEMBLY
2	16-20500	STUD, REAR - TOP COWL TO COVER
3	16-20353	STUD, FRONT-TOP COWL TO CRANKCASE
4	25-20116	GROMMET, CHOKE KNOB
5	37-46023A1	DECAL SET, TOP COWL
6	23-20326	SPACER, TOP COWL STUD
7	12-69057	WASHER, TOP COWL STUD (3/4" O.D.)
8	12-20583	WASHER, TOP COWL STUD (1/32" THICK)
9	11-8267089	NUT, TOP COWL FASTENING
10	20155	RETAINER, STARTER SPRING
11	24-29340T02	SPRING, STARTER REWIND
12	23-28912	BUSHING, SPRING GUIDE
13	50-30994	SHEAVE ASSEMBLY
14	30596	PAWL, STARTER
15	13-36206	WASHER, WAVE-STARTER PAWL
16	23-28919	BUSHING, NYLON-SHEAVE SHAFT SPACER
17	45477A1	SPACER, SHEAVE SHAFT
18	26179	RETAINER, WAVE WASHER
19	12-26180	WASHER, WAVE WASHER RETAINER
20	13-20160	WASHER, WAVE-RETAINER TENSION
21	30595	PLATE, RETAINER STARTER PAWL
22	45477A1	SHAFT, SHEAVE
23	50-12066Q10	STARTER CABLE ASSEMBLY
24	28747	HANDLE, STARTER CABLE
25	79470A1	RETAINER, STARTER CABLE AND HANDLE
26	28944	HANDLE, TOP COWL
27	10-28667	SCREW, HANDLE TO TOP COWL
28	10-56500	SCREW, HANDLE TO TOP COWL
29	11-8267089	NUT, HANDLE FASTENING SCREW
30	28967	SCREEN, VENT-TOP COWL
31	10-26668	SCREW, VENT SCREEN TO TOP COWL - SEE NOTE #1 BELOW
32	14-20165	TAB WASHER, SHEAVE SHAFT NUT
33	11-20166	NUT, SHEAVE SHAFT (LEFT HAND THREAD)
34	30045	PLATE, ROPE GUIDE (SEE NOTE #2 BELOW)
35	10-28642	SCREW, DRIVE-ROPE GUIDE PLATE TO TOP COWL

100-Hour / Annual Service Checklist

Regular maintenance keeps your Mercury 300 350 running reliably season after season. Most of these tasks can be performed with basic tools and the factory service manual.

Replace water pump impeller and inspect wear plate
Change engine oil and oil filter (check drain plug washer)
Replace spark plugs and check ignition timing
Drain and refill lower unit gear oil; inspect for water contamination
Inspect fuel lines, primer bulb, and fuel filter for deterioration
Check and replace sacrificial anodes (zinc or aluminum)
Inspect propeller for damage; check shaft seal and cotter pin
Check valve clearance (refer to service manual for specifications)
Lubricate all grease points (steering, tilt tube, shift linkage)
Inspect control cables and throttle/shift linkage for smooth operation

Pro Tip: Always flush the engine with fresh water after saltwater use — even a quick 10-minute flush significantly extends component life.
Pro Tip: Use fuel stabilizer in the tank before winter storage, and fog the cylinders to prevent internal corrosion during extended periods of non-use.

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