Mercury 90-HP Starting Problems
Posted: Mon Jul 17, 2023 8:52 am
My 2002 Mercury 90 two-stroke-power-cycle outboard engine with less than 200 hours has failed to start twice in the last week. To me this indicates the cause of the no start is due to the gasoline fuel, or due to the carburetors, or due to the spark ignition.
Q1: where can I start the diagnosis of the cause of the no start condition?.
BACKSTORY
The Mercury 90 typically will initially start, but stall after running for five seconds. Any attempts after that to start will fail without even even a hint of ignition. Fuel drips into the lake.
The first occurrence of non-starting start like this, I waited five minutes before trying again. I set the throttle at half-throttle. The engine begrudgingly started, but ran very roughly. I got underway; I could feel that we only had two cylinders firing, then the third cylinder came on. My impression was a carburetor was flooded and was clearing out, or a spark plus was bad.
I replaced all three spark plugs.
The second occurrence of rough starting was similar. Gasoline dripped into the lake. On this occassion, I waited 30-minutes before trying again, but the engine did not start. A buddy towed me back to my dock.
[Back at the dock] I pulled off the air box cover and tried tilting the motor up. A steady but small stream of gasoline ran out of the lower carburetor air intake. The fuel continued to spill for 15 seconds, and then I tilted back to level.
I let the engine sit overnight. The next morning it started immediately, although it's idling rough and I didn't leave the dock. I should point out that in between these two incidents the engine started and ran normally.
[Survey question about how often this has happened to any reader has been removed.]
It seems like the abundance of fuel indicates a fuel control problem.
Q2: what regulates fuel flow to the carburetors?
Q3: is excess fuel a normal result of the repeated attempted starts and this is a spark problem, especially since when failing to start there is not a hint of anything firing?
If the cause is electrical, it's obviously intermittent, and has not ever happened when running - only when starting - so it's hard to imagine a root cause.
Q4: where do I look?
Q5: fuel or spark?
Q6: what can I check without waiting for another failure?
I should add that the boat lives here permanently; there is no trailer; there is no trustworthy Mercury service on the lake. I'm probably on my own here.
Many thanks for ideas.
Q1: where can I start the diagnosis of the cause of the no start condition?.
BACKSTORY
The Mercury 90 typically will initially start, but stall after running for five seconds. Any attempts after that to start will fail without even even a hint of ignition. Fuel drips into the lake.
The first occurrence of non-starting start like this, I waited five minutes before trying again. I set the throttle at half-throttle. The engine begrudgingly started, but ran very roughly. I got underway; I could feel that we only had two cylinders firing, then the third cylinder came on. My impression was a carburetor was flooded and was clearing out, or a spark plus was bad.
I replaced all three spark plugs.
The second occurrence of rough starting was similar. Gasoline dripped into the lake. On this occassion, I waited 30-minutes before trying again, but the engine did not start. A buddy towed me back to my dock.
[Back at the dock] I pulled off the air box cover and tried tilting the motor up. A steady but small stream of gasoline ran out of the lower carburetor air intake. The fuel continued to spill for 15 seconds, and then I tilted back to level.
I let the engine sit overnight. The next morning it started immediately, although it's idling rough and I didn't leave the dock. I should point out that in between these two incidents the engine started and ran normally.
[Survey question about how often this has happened to any reader has been removed.]
It seems like the abundance of fuel indicates a fuel control problem.
Q2: what regulates fuel flow to the carburetors?
Q3: is excess fuel a normal result of the repeated attempted starts and this is a spark problem, especially since when failing to start there is not a hint of anything firing?
If the cause is electrical, it's obviously intermittent, and has not ever happened when running - only when starting - so it's hard to imagine a root cause.
Q4: where do I look?
Q5: fuel or spark?
Q6: what can I check without waiting for another failure?
I should add that the boat lives here permanently; there is no trailer; there is no trustworthy Mercury service on the lake. I'm probably on my own here.
Many thanks for ideas.