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Dead/defective battery effect on 40 yamaha

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yammyfan

Member
I have twin 40's and twin batteries, one for each. One battery has been going flat and requiring a jump to get starter motor going. If this battery has collapsed, will it stop the motor running, ie; rob the CD's of spark, when demand is high, ie; at high throttle settings?
I had this motor stop suddenly at 5000 rpm the other day. I thought it had seized, but it ran again after jumping from the good battery and starting it. Oil is full, cooling fine, etc.
 
Even a weak battery or loose terminals will slowly kill your powerpak/cdi box/ecu/emm, etc...
The year/model no. of motors will help specify correct terminology. But anyways, a dead battery is badly/deadly for all electronic modules that circulate current (voltage) to and from. A rectifier won't like to charge a block of lead for an example.
Change the battery and hope that the old one hasn't done extreme damage to the electronic brain (computer).
 
I think you will find that the motor only needs the battery for cranking !!--------------The battery has nothing to do with spark for ignition.------------That is looked after by the magneto.
 
well, with good battery she's crackling away happily out of the water and up to 3000 or so with forward engaged (for some load on the crank)....I still need a definite answer about "will a dead/defective battery kill a motor running at high revs/demand", because I want to eliminate oil starve...there were no alarms to indicate an oil supply problem...but I noticed more steam coming from this motor (out of the upper leg port at the rear) after a run at middle revs, than the other motor. She didn't FEEL hot at all...still cool around the base of the housing and upper leg.
When it happens, at revs above say, 4000, sometimes his motor will suddenly start to get louder, that is, like more demand or resistance is being exerted, for a few seconds before this "seizure" takes effect, and if throttled off straight away, will run fine. My ear is acute to any change in the sound of these motors. Would spark deprivation stop one CDi, or all, or all intermittently, creating this "stressed" sound before she stops, ie; drop every 2nd or 3rd spark?
One would think that seizing due to oil starve would be permanent and definite...why would this motor exhibit a hotter condition than the other, when tell-tale is strong? What stops a motor running at 5000 revs in about four seconds? Fuel starve? Would sputter and die more slowly. Oil starve? Would get hot and seize completely. No spark? Would stop instantly, or die over a few seconds...LIKELY...
Thanks for your suggestions people, and happy boating.
 
If they are automatic oil injected 2 stroke motors, then have the oil pump tested to see if it is / was working properly.
 
yes turned out there was water in the oil reservoir and in the oil pump, and my port motor was getting hot over about 2500 rpm and seizing briefly. I switched her off after the 2nd incidence and trolled home on the other motor. Bugger! Turns out compressions still fine, no apparent damage, very lucky I didn't cook it completely. Will run 100:1 in the fuel mix to be sure from now on, rather than retire the oil injection system altogether, just yet.
Thanks for your help, and I will learn to fix the easy thing first so the serious things don't "hide" behind them.
 
Yamaha's oil system is one of the best. You need to service your oil tanks on a yearly basis. That means removal of all oil, cleaning and replacing the filter. As for your batteries, the charging system on your engine is more of a battery maintainer. If you have a bad battery IE plates shorting intermittently, you will damage your engine due to extreme amperage over draw.

As for seizing briefly, if that was the case, it would be cheaper to pull your engine apart now voluntarily and have the damage corrected or wait for the engine to take itself apart.
 
well, the outboard mechanic said that this motor is slightly noisier than the starbord one, maybe as a result of the hot/dry incidents, and it wouldn't have done the internals much good, but might run like that for the next 20 years anyway. I believe taking it apart and fixing any damage now would be the right thing to do, but when and if she does go bang, I'll be repowering anyway.
 
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