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Dominick
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 1998 115hp johnson and at full throttle i have half

Customer Question

I have a 1998 115hp johnson and at full throttle i have half the power n sometimes it will just take off n run like it's suppose to then it shuts down Ive cleaned the carbs n replace fuel lines n bubble n spark plugs.
Submitted: 3 months ago.
Category: Boat
Expert:  Tan replied 3 months ago.

Hello Jason. My name is Tan.

This is a sign of an ignition failure. Do you have a timing light?

Could I get the engine model number also?

Customer: replied 3 months ago.
i do. J115tslecm
Expert:  Tan replied 3 months ago.

Ok what we need to do to start out with is check spark on all cylinders with the timing light. The way to do this is connect the timing light to each spark plug wire run engine and watch the flash of the timing light. The flash should be steady with no dead spots. If you find a cylinder misfiring swap that coil with a known good firing coil. Does the misfire move? If it moves the coil is bad if it stays then we have another ignition component failing.

If you have no misfire then you will have to do this test on the water running the boat.

Can you do these checks and do you understand the procedure?

Customer: replied 3 months ago.
Ive check it on the water by pulling off one spark plug wire at a time n u could tell on each of them when i did that I also pulled the linkage going under the flywheel forward n it ran better but not at full power i thought i had my timing light here but my brother has it
Expert:  Tan replied 3 months ago.

Do you have spark on all cylinders when you pull each plug wire? Does the engine slow down on each cylinder when you pull the plug wire?

Customer: replied 3 months ago.
it does slow down on each of them
Expert:  Tan replied 3 months ago.

Ok did you do this test when the engine was low on power? Have you tried choking the engine when low on power or squeezing the primer bulb?

Customer: replied 3 months ago.
n yes
Expert:  Tan replied 3 months ago.

Do this test advance the throttle and watch the timer base linkage. Does the timer base move when you advance the throttle at the same rate?

Customer: replied 3 months ago.
Expert:  Tan replied 3 months ago.

From your description you have an ignition issue. The choke and the primer bulb test eliminates fuel delivery. We really need to do the timing light test. So far by your tests there is nothing wrong with your engine. You have spark, fuel and compression.

Customer: replied 3 months ago.
This boat set for 3 years n when i parked it it was running fine n when i decide to redo the inside of the boat I started it up n it sounded fine it reved up n sounded good I was shocked. There is one more thing i did to it n that was change the ignition switch not all the wires matched up color for color and but it was the same amount of wires and it started up could that be a problem
Expert:  Tan replied 3 months ago.

Nope. The only thing the key switch does is turn the starter and ground the ignition. The rest of the wires to the engine are for the choke and the instrumentation. So the only thing that would cause an issue with the key switch wiring is the stop circuit. If that was an issue the engine wouldn't start.

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