Small engine starting problem


I need some ideas. It is a Yamaha atv. Battery shows 12.9 volts and turns the engine over fine, but won't start. When I hook up a battery charger it starts right up. Battery voltage when running is 14 volts.
Any ideas?
Hank <~~~knows something has to be wrong
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Hustlin' Hank wrote:

What's the voltage when it's turning over? Nearly zero I imagine. Get a new battery.
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I too think its a battery issue. I recently had an auxiliary battery with a bad cell. The surface voltage reading was about 12 volts, but as soon as you put a load on it, it would go down several volts. In your case, the voltage is enough to crank the engine, but if the voltage drops down simultaneously, it may not be giving the coil enough voltage to make a decent spark
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Hustlin' Hank wrote:

Try cleaning the battery cable, take them loose and clean where they contact the battery.
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On Jul 13, 6:49 pm, FatterDumber& Happier Moe

Put a known good battery in paralle with the ?? battery.
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Hustlin' Hank wrote:

Are you connecting the charger directly to the battery?
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14 v running means the charger system is probably good, you could check voltage as it starts, but its most likely a weak battery without any capacity, clean all connections first it could be something dirty corroded or loose now alllowing full amperage to the starter.
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I did replace a battery cable, and clean the terminals and also the terminals on the starter and solenoid no fix. I put in KNOWN good battery, no fix. I haven't tried jumping from another battery. I did find that the coil wire was twisted together and replaced it with a connector, no fix. I hook the battery charger directly to the battery, which is the only way to get it to start.
Starter turns just as fast with charger as without charger, or good battery. The coil was replaced thinking it was a weak coil.
I am sooooo confused.
Hank <~~~never seen this problem before
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Hustlin' Hank wrote:

I could be the valves need adjusting, there is a compression release on most small engines that allow for easier starting but the valves have to be adjusted to specs for it work properly. The added amperage from the additional battery might be enough to over come the extra compression. I've got an old riding mower with a twin cylinder B&S engine and it takes a three year battery to start it when the engine is hot, the one year batteries just don't have enough cranking amps. Check out some small engine forums. And it PMO that I can buy a car battery cheaper than the dinky battery for my riding lawnmower.
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On Jul 14, 4:18 am, FatterDumber& Happier Moe

I believe we've had the compression release debate before. It's common for engines that are started manually. I'm skeptical his atv has one but a look at an ipb would tell. Need the model number.
It sounds like a pretty strange problem. I would try taking some voltage measurements while cranking. At the battery and also at the ignition module. Most likely the 12v positive enters the ignition system at the module. As well as pull a plug and watch it for spark.
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Hustlin' Hank wrote:

Are you doing anything at all differently not related to the battery? It almost sounds like there is some safety device not allowing the engine to start. My motorcycle has a couple or so things like that.
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On my bike those all won't let it crank either. I've not seen a safety device that lets you crank the engine but prevents it from starting. That would be sort of stupid as the operator could easily run the battery down.
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Maybe a bad starter...loading a normal battery but having enough power with the charger to start?
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On Thu, 15 Jul 2010 04:24:41 -0700 (PDT), Bob Villa

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On Fri, 16 Jul 2010 17:10:42 -0400, snipped-for-privacy@snyder.on.ca wrote:

I had a "dragging starter" once. Armature bushings were bad and this seemed to cause problems. The starter and cable would get hot, acting foolishly.
I measured the Amp draw as the starter turned over ... I forget
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