Yamaha C90TLRY Looses power and shudders, then boat drops off plane.

[jkingry1]

Hello,

Motor: 1999 Yamaha C90TLRY 90hp 2 Stroke
Boat: 1996 Carolina SKiff 2180
Portable 6 gallon and 12 gallon gas tanks, problem occurs on either tank.

So this problem started occuring last week, I will plane the boat off and start cruising at speed and after a minute the engine start shuddering and shaking the boat as the rpms drop between 2 and 3k, the boat falls off plan and the shuddering continues until you pull back on the throttle to idle. After a few more tries like this you can not ever plane off it just shudders immediately and you have to idle home at around 7.5mph.

The gasoline is brand new and fresh. There is no external water seperator but there is no water in the fuel filter on the engine and everything looks clean.

I do not even know where to begin looking or how to test for issues, I have the service manual so I will be reading it tonight but if anybody can maybe share some tips for me to rule out things it would be great as the boat is in the water right now.

Thanks

jkingry

 

[robert graham]

Re: Yamaha C90TLRY Looses power and shudders, then boat drops off plane.

I run the same motor and first place I'd check would be fuel line restrictions and/or fuel line venting....Have you checked your fuel pump diaphragm for holes?...

 

[Capt Ken]

Re: Yamaha C90TLRY Looses power and shudders, then boat drops off plane.

Probably your alarm isn't working to warn you of overheating and it's going into safe mode.

 

[jkingry1]

Re: Yamaha C90TLRY Looses power and shudders, then boat drops off plane.

Hey guys,

Thanks for the replies, here is where I am at currently. I pulled the thermo switch and tested it with a pot of boiling water, it opens and closes perfect both times I tested it. I then checked the buzzer and just like Capt. Ken said it is dead, I tested it both by jumping the thermo switch wires and taking the buzzer off and wiring it straight to a battery.

So step 1 I have ordered a new buzzer, thermostat (it just needs this I am sure) and will change those out. Once I have the buzzer working I can narrow down if the engine is really overheating, I ran over the engine with a laser thermometer and found nothing over 110 degrees F but maybe it is somewhere I could not get to.

I will keep asking questions as I get further down the road.

Thanks

jkingry

 

[99yam40]

Re: Yamaha C90TLRY Looses power and shudders, then boat drops off plane.

not sure about the C90 but the pink wire on one of the switches going to ground is the one that was for the over heat on my C40 that caused it to go into RPM reduction and sound alarm

if it is not truly overheating then maybe a wire problem( going to ground).
measuring head area where temp switches are located should show if there is a over heat.
scale build up can cause hot spots
Stat can be tested in pot of water also to see if it functions in spec