96 DT8C overheated?

nabiul

Petty Officer 2nd Class
Joined
Jul 18, 2015
Messages
131
Here is what happened in chronological sequence.

I had the motor on a test stand with the waterline about half an inch above the cavitation plate.
I tried to start the motor with the choke on, the motor started, spun up to a high speed and then cut out. After repeating this several more times while also priming and fiddling with the low speed adjustment, the motor started and ran.
It was a bit smoky and smoke or steam started coming out of the water discharge, after a while this turned into water spraying out.

I stopped the motor and then did some spark tests for a few minutes, got strong sparks from both cylinders, the motor was more difficult to start with one cylinder only. I stopped the motor again and left it alone for a few minutes.

I went to start the motor again, I could feel the powerhead was still warm so I didn't use the choke. The motor started and ran but no smoke/steam came out of the water discharge. After 30 to 45 seconds a puff of smoke came out of the water discharge, the motor 'sneezed' and then cut out.

I started it again, this time alot of smoke/steam came out of the water discharge but it wouldn't turn into a stream of water. I began to worry after about 30-45 seconds of this, then the motor 'sneezed' again and cut out.

I started to worry that maybe the sneeze was the pistons binding inside or something being caused by overheating, so I took some water and sprinkled it over the cylinder heads and the water sizzled away. I did this a couple more times to several areas of the head which were also hot and then called it quits; I put the cover back on and left it to cool until tomorrow.

Did I overheat the motor? I had this motor on the water just the other day and it was barely warm to the touch under WOT.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,211
my thoughts are you need to look up lean sneeze on a 2 stroke outboard on the web
 

nabiul

Petty Officer 2nd Class
Joined
Jul 18, 2015
Messages
131
I can try adjusting the carb, but what about the high amount of heat? I know that under normal operation you are supposed to be able to touch the powerhead for a few seconds before it feels too hot; from what I saw with the water it looked like I would've been burned instantly if I touched the head.
 

nabiul

Petty Officer 2nd Class
Joined
Jul 18, 2015
Messages
131
Ah crap, I fear I have made a critical error. Looking at the parts diagram, the water pump is clearly 4 or 5 inches above the water intake at the cavitation plate.
 

nabiul

Petty Officer 2nd Class
Joined
Jul 18, 2015
Messages
131
I put the pump back in and got a bigger bucket for the motor. The water appears to be coming out of the discharge at the same rate as when I bought it so maybe the pump was like that all along and the motor is no longer overheating.

EDIT: The motor is fine, it just needed to get the old gas out of the carburetor and some time to warm up. I was jumping to conclusions without being thorough.
 
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