1989 70 hp Evinrude Overheating:

[TwoRivers]

Over the past winter I replaced the water pump and fuel pump on my1989 70.
Both pumps are OEM.
The original fuel pump was a bi passed vro replaced with non vro pump.
Changed all the fuel lines.

Compression is 120 across all cylinders.
Good spark. Motor is peeing strong. I removed tstat and checked in hot water.
Motor starts instantly and runs well at low rpm’s. Get up to or over 4k and shortly the steady overheat horn goes off and motor dies down.
I’m thinking it’s leaking air somewhere?
When the overheat horn goes off I check the top of the motor temperature with a surface thermometer and it’s hot. Around 172.
When I pull the plugs it looks like number 2 cylinder is running lean.
I pulled the main jet from number 2 carb it didn't appear to be dirty but I cleaned it anyways.
At idle when I spray carb cleaner around the #2 carb gasket the motor will stumble. I've ordered new carb gaskets.
I've gone over the fuel lines and none appear to be leaking fuel or air.
I relocated the tell tale to the top of the engine years ago. My new water pump kit included two plastic elbows for the tell tale. One has a larger orifice that the other. The one I've been using appears to be the larger one. Does it matter which one I use? Could it be an issue?
Any ideas how to troubleshoot?
Could it be something other than an air leak?
Thanks in advance for your consideration.

 

[cwella]

The lean #2 plug and carb cleaner test are the biggest clues. It sounds more like a fuel/air issue on #2 than a cooling problem.

I would start with:
• Replace the #2 carb gasket since spraying it affects idle
• Check #2 float height, needle/seat, and all internal carb passages
• Verify the main jet size matches the other carbs
• Inspect reeds if the carb repair does not fix it

The tell tale elbow size is unlikely to cause this; it only shows water flow, not full cooling system performance.

Also check the water pump installation, water tube seals, and cooling passages, but fix the lean condition first. Running lean at 4000+ RPM can quickly damage a 2 stroke.

 

[TwoRivers]

The lean #2 plug and carb cleaner test are the biggest clues. It sounds more like a fuel/air issue on #2 than a cooling problem.

I would start with:
• Replace the #2 carb gasket since spraying it affects idle
• Check #2 float height, needle/seat, and all internal carb passages
• Verify the main jet size matches the other carbs
• Inspect reeds if the carb repair does not fix it

The tell tale elbow size is unlikely to cause this; it only shows water flow, not full cooling system performance.

Also check the water pump installation, water tube seals, and cooling passages, but fix the lean condition first. Running lean at 4000+ RPM can quickly damage a 2 stroke.

Thanks for your reply.
New gaskets came in today. I'll install tomorrow and try to take the boat out for a spin.
What do you think about timing?
My motor calls for 19 degrees BTDC.
Either 1990 or 91 they changed to 17 BTDC.
Was there a SB regarding changing the 1989 model timing?
I agree with you that it's not a cooling issue.