1996 Yam 115 Thermo switch question

[LewisB]

Hi Guys,

A quick summary of my engine snag and then the question.....Over the last summer my yamaha 115 (1996) has been running fine at 5200 rpm then intemittently dropping to about 3200. It doesnt come off the plane and nothing alarms, just loses about a 1/3 of the power. Sometimes it is for just a few seconds, others for 10 minutes.

I've cleaned the carbs (twice) checked the fuel lines, rebuilt the fuel pump and have checked that it still does this on both internal and external tanks (it does).

I've now noticed that on the stbd side thermo switch, the black wire connection looked corroded, i've cleaned it up and refitted it. Have not had the chance to run it yet.

My question is could this intermittently cause the loss of power? And if so should it be alarming? I am not hearing the alarm. I'm hoping that this is the root of the problem but the cynic in me tells me its gonna cost me more!

thanks in advance for any thoughts you guys have on this,

Regards,

Lewis

 

[JUSTINTIME]

Re: 1996 Yam 115 Thermo switch question

check alarm

 

[LewisB]

Re: 1996 Yam 115 Thermo switch question

I'll check the alarm as soon as i get to the boat - if the alarm is not working, do you think that the corroded connection could cause the intermittent loss of power?

Lewis

 

[JUSTINTIME]

Re: 1996 Yam 115 Thermo switch question

yes

 

[LewisB]

Re: 1996 Yam 115 Thermo switch question

Got to the boat and checked the alarm, it works fine - which is a relief as i was worried i was cooking the engine!

I'm still hoping cleaning that connection up would solve it but as i have not heard an alarm on loss of power i guess this wasn't the problem

Back to the drawing board again. I am thinking maybe about taking out the carbs for a 3rd time and rebuilding them with the kits rather then just taking them apart and cleaning them as i've done so far.

If you've got any more ideas on what to look for or previous experiences you could clue me up on I'd be very grateful.

cheers,

Lew

 

[rodbolt]

Re: 1996 Yam 115 Thermo switch question

I have to dissagree.
a corroded black wire at the thermo-swticth simply CANNOT and will not cause a miss nor any RPM reduction.
think about it,your dealing with a SWITCH, a simple on/off device.
its normally open(off), when the wax pellet inside expands enough with heat it closes(on) and allows a path from ground,through that black wire,through the thermo-switch,through the pink wire (turns to gray in the harness) to the CDI and the audible alarm horn that has key on 12V+ on the otherside.
so if that black wire was corroded and not making contact your CDI would simply always see the thermo-switch as off and never enter RPM reduction if the switch closed (on).
to test turn the audible, the key on,unplug the black and pink thermo-switch connectors,jump the two harness side connectors together. horn should sound and the visual indicate(if equipped) will illuminate.
but if one ground wire is corroded I would suspect others and they can cause an intermittant engine miss even on simple ADI ign systems.
I would also check the oil warning system,if applicable.
after that check all pulser coil outputs,charge coil,both high and low speeds,and CDI output voltages.
if all are stable at the problem RPM check for fuel restrictions or air leaks starting at the cowl connector.
and yes it wont be the first set of carbs that had to come apart a few times.

 

[LewisB]

Re: 1996 Yam 115 Thermo switch question

Thanks for the reply Rodbolt, I got it to alarm by doing just as you suggested. The issue i've got with trying to test the engine is that i can't reproduce the problem....driving me insane!! It is so intermittent.

I think I'll open up the fuel tank, and starting with the pick up pipe, check all the fuel system upto and including rebuilding the carbs again.

When it happens the boat seems to be under load, for example 6 to 8 people on board or heavier seas.

The electrics are something i've not had a look at as thats outside my comfort zone to be honest. I was thinking that as it is intermittent that it would not be electrical - is that nieve?!

I've checked all the wires that I can see and there was only the one corroded one (that i could see). All others seem fine and secure.

Other than the intermittant loss of power, it runs sweet. Frustrating.

Any advice would be great.

Lewis