This is a basic wiring diagram for a Mercury Racing V6 2-stroke 2.0, 2.4, 2.5 Liter race outboard running a 12v ignition system along with 24 volts for faster trim and faster starting.

These are the original Mercury Racing Factory OEM Specs for the V6 2.5 Liter 300 Drag outboard. It also includes other recommendations for oil, spark plugs, timing advance, rpm rev limiter, water pressure at WOT, battery sizing, charging system output.

To check the compression on a 2-stroke outboard, you can try these steps: Remove all spark plugs, clean, and dry the spark plug Screw in the compression tester finger tight, one cylinder at a time Ignition off, open the throttle to 100% Crank the engine about 4x, until the gauge stops increasing Record the reading Repeat for each cylinder Here are some tips for checking compression on an outboard engine: Warm the engine before doing the test Count the pulses when cranking Use the same amount of pulses for each cylinder A good compression reading for a 2-stroke engine is between 110 and 130 psi, as the color change from red to green indicates on the Buckshot Racing #77 Compression Gauge. The difference between the highest and lowest readings should be no more than 10%. Low compression can be caused by a leaking piston, piston ring, camshaft, head gasket, or valves. To test for this, you can add some oil to the cylinder. If compression is low, it's recommended not to run the engine. Pull the cylinder for further inspection. It could be time for a build before more damage is done by running the motor.

These are the factory Mercury Racing 2.5 Liter Torque Specs for rebuilding a V6 2-stroke race outboard.

This wiring harness color chart is for all 1991 to 2000 EFI "Laser" front-injected Mercury ​2.5 Liter​ 2-Strokes. ​Most of this fuel injection wiring diagram is common with other Mercury models with ECUs including the 2.4 Liter.

Mercury Marine Mercruiser Mariner ​3-Wire ​Trim, Tilt, K-Plane Tabs Pump​ Wiring Harness Diagram

Detonation in a 2-cycle outboard engine resembles the “pinging” heard in an automobile engine. It can be otherwise described as a tin-like “rattling” or “plinking” sound but most of the time you can't hear it to due to the engine, wind, and water noises. Detonation is an explosion of an unburned portion of the fuel/air charge after the spark plug has fired. Detonation creates severe shock waves in the engine and these shock waves often find or create a weakness that can quickly destroy the top of a piston, cylinder head/gasket, piston rings or piston ring lands, piston pin, and roller bearings. A few of the most common causes of detonation in a marine 2-cycle outboard or jet boat powerhead are as follows: 1. Over-advanced ignition timing. This could happen simply by the top throttle arm or the linkage becoming loose and moving the timing adjustor. Or the timing advance box malfunctioning, all unsuspectedly. 2. Use of low-octane gasoline. The lower the octane the faster the fuel burns, and if the fuel burns before the piston has a chance to reach top dead center, it pounds the top of one or more pistons. 3. Propeller pitch too high (engine RPM below recommended maximum range). AKA lugging the motor. 4. Lean fuel mixture at or near wide-open throttle. 5. Wrong or bad spark plugs (heat range too hot, incorrect reach, gap, or cross-firing). 6. Inadequate engine cooling (deteriorated cooling system, or bad water pump). 7. Combustion chamber/piston deposits (result in higher compression ratio). There are other reasons for blown outboard motors, stuck or melted pistons, and broken rods; feel free to email STVracer @yahoo.com photos and we can help you identify what went wrong.

Your Throttle Position Sensor (TPS) TPS can be adjusted using a digital meter and our is available for sale on this site. Analog (needle) type may be used although it may be difficult to read the low voltage setting accurately with most meters. 1. Disconnect TPS from the EFI harness. 2. Connect digital using TPS Test Lead Assembly (a) (P/N 91-816085) between TPS connector (b) and EFI harness connector (c). Set voltmeter to 2 DC volts. 3. Disconnect the TAN/BLACK engine head temperature sensor leads located on the port cylinder head. 4. Turn the key to the “ON” position. 5. Loosen screws (1) securing TPS to manifold. 6. Rotate TPS fully clockwise (holding the throttle shaft in a closed position). Your voltmeter should read .200 - .300. If the readout is not within specifications, adjust TPS to obtain a readout of .240 - .260. 7. Tighten TPS screws to 20 lb. in. (2.0 N·m) holding the correct tolerance. 8. Disconnect the remote control cable from the throttle lever. 9. Slowly move the throttle lever to the full open position while monitoring the voltage reading. The voltage reading should increase and decrease smoothly. 10. Set the volt meter to 20 DC volts. Maximum voltage reading at full throttle is approximately 7.46 volts. 11. Remove the test leads and reconnect the TPS harness to the EFI harness. 12. Reconnect TAN/BLACK engine head temperature sensor leads located on the port cylinder head. NOTE: If the engine appears to run too rich or too lean, TPS can be readjusted. Decreasing voltage yields a leaner mixture. Increasing voltage yields a richer mixture.

The mechanical fuel pump on 1976 to 2005 Mercury 135, 150, 175, 200, 225 HP 2-Stroke V6 outboards (Black Max 2.0 and 2.4 Liter and 2.5 Liters) is a crankcase-pressure-operated, diaphragm-type pump. Crankcase pulsating pressure (created by the up-and-down movement of the piston) is transferred to the fuel pump by way of a passage (hole) between the crankcase and the fuel pump. Some symptoms of a bad fuel pump or restricted (lean) fuel flow include: 1 - Loss of fuel pump pressure 2 - Loss of power 3 - High-speed surging 4 - Preignition/detonation (piston dome erosion) 5 - The outboard cuts out or hesitates upon acceleration 6 - Outboard runs rough 7 - Outboard quits and cannot be restarted 8 - Outboard will not start 9 - Vapor lock Remove, Clean, Inspect, Rebuild, Install: 1. Clean fuel pump housing, check valves, pulse chamber and pump base in solvent, and dry all but check valves with compressed air. 2. Inspect each check valve for splits, chips, and proper sealing against the pump housing. 3. Inspect boost springs for weakness or breakage. 4. Inspect the fuel pump housing, pulse chamber, and base for cracks or rough gasket surface and replace if any are found. 5. Inspect the fitting on the fuel pump housing for loosening or any signs of fuel or air leaks. Replace or tighten the fitting if a leak is found. 6. Insert new retainer from the rebuild kit through plastic disc and rubber check valve. 7. Install new check valves and retainers into the fuel pump body. 8. With the new retainer installed in the pump body, break the retainer rod from the retainer by bending sideways. 9. Install the new rod into the retainer cap and, use a small hammer and punch to tap the rod down into the retainer until flush with the top of the retainer. 10. Place the boost spring into the pump body and place the cap onto the boost spring. 11. Assemble the remainder of the components as shown and install retaining screws thru to align. 12. Install the rebuilt pump onto the powerhead. Torque to 55 Ib. in. (6.0 N·m). 13. Install hoses onto proper fittings and secure them with straps. 14. Make sure you run the engine and check for leaks before launching the boat.

Here is a simple way to check the condition of a 12-volt outboard marine battery in your boat with a simple battery checker. The motor is off: 1. Connect the battery checker to the battery terminals. The red connector goes to the positive terminal and the black connector goes to the negative terminal. 2. The light that illuminates under the "battery condition" will indicate the battery's approximate voltage charge. 3. A fully charged and healthy battery should read 12.6V. A partially discharged battery that needs recharging would have a 12.1V to 12.5V level. The motor is running: 1. Connect the battery checker to the battery terminals. The red connector goes to the positive terminal and the black connector goes to the negative terminal. Make sure it is safe to run the motor. 2. The light that illuminates under the "charger output" will indicate the stator's approximate voltage charge. 3. A healthy charging system should read 13.2V to 14.5V. A charging system that may need attention might read under 13.1V or over 14.6V at idle. Please note, as a reference, a 12-volt lead acid battery will deliver about 12.7 volts when fully charged, but only about 11.6 volts at 20% capacity. Meanwhile, a lithium battery will deliver 13.6 volts when fully charged, and 12.9 volts at 20% capacity.

This is a printable Mercury V6 Outboard Single Trim Tilt Ram (Long) Assembly​ and exploded view parts diagram.

Instructions: 1. Connect one lead to the yellow/red wire on the terminal of the solenoid. Be careful as these connections are close to the hot terminal! 2. Connect the other lead to the 5/16" terminal on the solenoid with the HOT battery cable. This is the heavier gauge RED cable coming from the positive side of your battery. 3. Once clear of the powerhead, moving parts, propeller, and opened gas fumes, push the Remote Outboard Starter Switch to crank over the motor.