A 1989 Johnson GT150 outboard motor underwent extensive repairs, including carburetor, water channel, and fuel tank cleaning, along with replacement of the power pack, timer base, stator, and rectifier/regulator. After these repairs, the motor initially started and ran smoothly. However, after removing and reinstalling the middle carburetor to address a fuel leak, the motor no longer starts. Instead, it backfires several times before ceasing to make any attempt to start. The engine spins freely and exhibits normal exhaust flow through the propeller.
Several troubleshooting steps have already been taken:
- Power Pack: Tested and one replaced.
- Spark Plugs: New Champion plugs installed, inspected for rich condition, cleaned, and reinstalled.
- Kill Switch: Disconnected to rule out as a cause.
- Solenoid: Bypassed by jumping the red plug to ensure proper engagement.
Despite these efforts, the Johnson GT150 still refuses to start. The problem seemingly arose after addressing a minor fuel leak on the middle carburetor. This suggests the issue may lie within the fuel system or ignition system related to the carburetor.
Possible causes for this no-start condition after carburetor work on a Johnson GT150 include:
- Incorrect Carburetor Reassembly: Double-check the reassembly of the middle carburetor, ensuring all components are correctly installed, gaskets are properly seated, and linkages are functioning smoothly. Pay close attention to the float and needle valve, as these components regulate fuel flow into the carburetor bowl.
- Fuel Delivery Issues: While new fuel lines and pumps were installed, it’s possible an issue has developed within the fuel system, especially considering the prior fuel leak. Verify proper fuel flow from the tank to the carburetors. Check for clogged fuel filters, pinched lines, or a malfunctioning fuel pump. Ensure the primer bulb is firm and pumping fuel effectively.
- Air Leaks: An air leak in the intake manifold or carburetor gaskets can disrupt the fuel-air mixture, preventing combustion. Inspect for cracks or damage to these components.
- Ignition Timing: Although the timer base was replaced, it’s possible the ignition timing is still incorrect. Verify the timing is set according to the manufacturer’s specifications.
- Carburetor Synchronization: With multiple carburetors, ensuring they are synchronized is crucial for proper engine operation. Improper synchronization can lead to uneven fuel distribution and starting problems.
Further diagnostic steps to consider:
- Compression Test: Perform a compression test on all cylinders to rule out internal engine damage.
- Spark Test: Verify strong spark at each spark plug using a spark tester. This will confirm the ignition system is functioning correctly.
- Fuel Pressure Test: Test the fuel pump pressure to ensure it meets the manufacturer’s specifications.
Resolving the no-start issue on this Johnson GT150 likely requires a systematic approach focusing on the fuel and ignition systems, particularly around the recently serviced middle carburetor. Addressing potential problems related to fuel delivery, air leaks, ignition timing, and carburetor synchronization should be prioritized. If the problem persists after these checks, a compression and spark test will help determine if further internal engine diagnosis is necessary.
