c90tlrv surfing before getting on plane

Joined
Mar 17, 2019
Messages
4
I have a 97 Yamaha 2 stroke 90hp. My motor will start and run at low rpms. But when I give it throttle it will only go about 7mph for maybe 20 minutes. After it warms up it will surge in and out for about 30 seconds and take off and go about 35-40mph. After that it will run good the rest of the day no matter how long I stop and fish or run for.
I have a new
-portable tank and fuel hose
-fuel joint connector
-fuel pump
-fuel filter
-2 new ignition cylinders
-spark plugs
also I just had the carbs rebuilt professionally.
After the guy rebuilt the carbs he said he took it out and ran 40mph right off the bat. Only thing I did was take off fuel tank off fill it up and put it back on afterwards and same problem.
Plese help (3 mechanics have had and couldn't fix it)
 

rejesterd

Petty Officer 2nd Class
Joined
Sep 20, 2018
Messages
142
Hello.

So it seems to be associated with the engine being cold, but after it heats up, the problem goes away. However, 20 minutes is a long warmup time. I'm wondering if your thermostat is stuck open (or not even installed). That would cause the engine to take a long time to reach the proper temperature. That's what I would check at this point, assuming that 20-minute period is like clockwork. Check the thermostat and the pressure control valve (both are in the same housing). It's right near the top of the cylinder head cover:

https://www.yamahaonlineparts.com/o...0ea08e/846a5252-406d-41b2-b4af-c7fa0365a45f/y

Good luck.
 
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