1988 Johnson 70 HP Outboard: Problems & Solutions

by Alex Braham 50 views

Hey guys! If you're here, you're probably dealing with some issues with your 1988 Johnson 70 HP outboard motor. Well, you've come to the right place! This trusty engine has powered countless boats over the years, but like any piece of machinery, it can run into problems. Let's dive into some common issues, how to troubleshoot them, and potential solutions to get you back on the water.

Common Problems and Troubleshooting

First, let's talk about the kinds of problems you might run into with your 1988 Johnson 70 HP outboard. These old motors are known for their reliability, but time and use can take their toll. Fuel system issues, ignition problems, and cooling malfunctions are among the most frequent culprits.

Fuel System Issues

One of the most common headaches with any outboard, especially one of this vintage, is the fuel system. Old fuel lines can crack, carburetors can get clogged, and fuel pumps can weaken over time. Any of these issues can lead to hard starting, poor performance, or even a complete failure to run.

  • Symptoms: Hard starting, rough idling, stalling, lack of power, or the engine not starting at all.
  • Troubleshooting Steps:
    1. Check the Fuel: Start with the basics. Is the fuel fresh? Old fuel can gum up the works. Drain the fuel tank and replace it with fresh gasoline.
    2. Inspect Fuel Lines: Look for cracks, leaks, or kinks in the fuel lines. Replace any damaged lines.
    3. Fuel Filter: A clogged fuel filter restricts fuel flow. Replace the fuel filter regularly as part of your maintenance routine.
    4. Fuel Pump: The fuel pump delivers fuel from the tank to the carburetor. If it's weak, the engine won't get enough fuel, especially at higher speeds. Test the fuel pump's output. If it's below spec, replace it.
    5. Carburetor: The carburetor mixes fuel and air. Over time, it can become clogged with varnish and deposits. Clean the carburetor thoroughly. If cleaning doesn't solve the problem, you might need to rebuild it with a carburetor kit.

Ignition Problems

Next up, let's tackle ignition issues. The ignition system is responsible for creating the spark that ignites the fuel-air mixture in the cylinders. Problems here can range from a weak spark to no spark at all, resulting in a no-start condition or poor running.

  • Symptoms: Engine won't start, misfires, runs rough, or lacks power.
  • Troubleshooting Steps:
    1. Spark Plugs: Start by inspecting the spark plugs. Are they fouled, cracked, or worn? Clean or replace them as needed. Make sure you're using the correct spark plug type for your engine.
    2. Spark Plug Wires: Check the spark plug wires for damage or corrosion. Make sure they're securely connected to the spark plugs and the distributor (if equipped) or coil packs.
    3. Coils: The coils provide the high voltage needed to create a spark. Test the coils with a multimeter to check their resistance. If a coil is bad, replace it.
    4. Timer Base/Sensor: The timer base/sensor tells the engine when to fire the spark plugs. If this is faulty it can cause all kinds of issues.
    5. CDI Unit: The CDI (Capacitive Discharge Ignition) unit controls the timing and intensity of the spark. If the CDI unit is failing, it can cause intermittent or complete spark loss. Testing a CDI unit can be tricky, and you might need specialized equipment. Sometimes, the easiest way to diagnose a CDI problem is to replace it with a known good unit.

Cooling System Malfunctions

Overheating is a major killer of outboard motors. The cooling system keeps the engine at the proper operating temperature. If it's not working correctly, the engine can overheat, leading to serious damage.

  • Symptoms: Overheating, steam or excessive heat from the engine, temperature alarm sounding.
  • Troubleshooting Steps:
    1. Water Pump Impeller: The water pump impeller is responsible for circulating water through the engine. Over time, the impeller can wear out or become damaged. Inspect the impeller and replace it if necessary. This is a routine maintenance item that should be done every few years.
    2. Thermostat: The thermostat regulates the engine's temperature. If it's stuck closed, the engine will overheat. If it's stuck open, the engine might run too cool. Test the thermostat and replace it if it's not working properly.
    3. Water Passages: Check the water passages in the engine block and cylinder head for obstructions. Salt, sand, and corrosion can build up over time, restricting water flow. Flush the cooling system with a descaling solution to remove deposits.
    4. Check the telltale: The telltale (the small stream of water that comes out of the engine) indicates that the water pump is working. If there is no water coming out of the Telltale, it means there is a blockage or the water pump is not working correctly.

Other Potential Issues

Beyond the big three (fuel, ignition, and cooling), here are a few other areas to investigate:

  • Low Compression: Low compression in one or more cylinders can cause poor performance. Use a compression tester to check the compression in each cylinder. If compression is low, it could indicate worn piston rings, damaged valves, or a blown head gasket.
  • Electrical Problems: Check all electrical connections for corrosion or damage. Clean and tighten any loose connections. Use a multimeter to check for voltage drops in the wiring.
  • Mechanical Issues: Inspect the propeller for damage. Check the lower unit oil for signs of water intrusion. If the lower unit oil is milky or discolored, it indicates a leaking seal.

Maintenance Tips for Your 1988 Johnson 70 HP

Preventive maintenance is key to keeping your 1988 Johnson 70 HP running smoothly for years to come. Here are some essential maintenance tasks:

  • Regularly change the lower unit oil.
  • Grease all moving parts.
  • Inspect and replace the water pump impeller every two years.
  • Use fuel stabilizer, especially when storing the motor for extended periods.
  • Flush the engine with fresh water after each use, especially in saltwater environments.
  • Keep the engine clean and protected from the elements.

Parts and Resources

Finding parts for a 1988 Johnson 70 HP outboard is usually not too difficult. Many online retailers and local marine shops carry parts for older outboards. Be sure to have your engine's model number handy when ordering parts to ensure you get the correct ones.

  • Online Retailers: Websites like MarineEngine.com, eBay, and Amazon are great resources for finding parts.
  • Local Marine Shops: Your local marine shop can often order parts for you or provide advice on troubleshooting.
  • Service Manual: A service manual is an invaluable resource for repairing your outboard. It contains detailed instructions, diagrams, and specifications.

Conclusion

Troubleshooting a 1988 Johnson 70 HP outboard motor can seem daunting, but with a systematic approach and a little patience, you can often diagnose and repair many common problems yourself. Remember to start with the basics, check the easy things first, and don't be afraid to ask for help from experienced mechanics or online forums. With proper care and maintenance, your trusty Johnson 70 HP will keep you boating for years to come. Happy boating, and may your wrenching always lead to smooth sailing!