97 2 stroke 40 hp 3 cyl. bogging after 1-2 mins at WOT

[wdrennan09]

Hey guys new to the forum but I have heard there are some guys on here that have a wealth of knowledge and I need some help diagnosing a problem. C40TLRV 40 hp 2 stroke 3 cylinder will crank on first turn, idle fine for an extended amount of time and open up, get on plain but after about 1-2 minutes running wide open it begins to bog down and will stay like this. However if you come back down to idle speeds for a couple of minutes and open her back up it will run like a top again only to start it again after another 1-2 minutes.


To give you a little background, I am a do It your selfer but very green to outboard motors, however have managed to recently clean he carbs and replaced impeller. Changed impeller bc his summer I was on the MS river ad ran it through some pretty shallow water on san bar and took in quite a bunch of sand, clogged lines and had to clean it out and replaced impeller. Carb and fuel system seemed to be running fine but left ethanol gas in the motor for quite while and decide to clean as preventable maint. I did not have this bogging problem until I cleaned the carb. and changed impeller/clogged it with sand. Also to note I tinkered with the idle screw and reset the air screws on the carb to 1-3/4 turns (factory recommendations) they were at somewhere around 3 turns. I also replaced fuel pump and filter.

I have heard these older motors have a safe mode and run at only lower rpm when they run hot, which Is why I am putting info about the impeller/cooling problem.

Another strange note I have also noticed it does start to bog down like this a couple of times when you turn it real sharp while on plane, May be a strange coincident.

Any idea what this could be ? Any help would be appreciated.
Thanks in advance.

[99yam40]

Being it is remote control ,you should have a buzzer in the control unit that should sound if it overheats.
Test to see if it works.
There is a pink wire on one of the temp switches on the head, take it loose and ground it with the key turned to the on position. The buzzer should sound.
If it does not fix it so you can tell if it is overheating.

When you replaced the impeller did you use the kit?
cup and wear plate along with orings and gaskets need replacing also to make sure it seal properly.
If there is any sign of melting on the plastic housing, replace it also.

Thermostat and temp switches can be tested to see if they meet spec.

Sometimes pulling the stat and dropping lower unit so you can hook a hose to the pipe leaving the water pump and flushing with lots of water and shooting some compressed air into the water stream going in will move stuff around inside the motor enough to flush it out, if there is sand etc settled into places that restrict flow
Let us know what you find.

[wdrennan09]

I only replaced the impeller and did not buy the kit. This motor has been converted to a tiller steer however it still has the plug for a remote steer controls. So I am going to assume I do not have an alarm on the actual motor if not pluged to a remote steer ?

I did flush the pipe out going to motor when I changed impeller and when running the motor seems to have a good stream coming from it.

In your personal opinion, does this sound like a fuel problem or a cooling problem ?

I was leaning more toward cooling but could be very wrong.

[ausnoelm]

Is the fuel tank vent open and clear?

[wdrennan09]

Yes it is opened and seems to be clear.

[99yam40]

the temp switch is normally open contact, closed when temp is too high.
Check it when the problem shows up to see if it is open or closed.

Or disconnect the pink wire while problem is there to see if that make a difference
Or use a temp gun to check temp of area the switch is looking at