Bike won't start unless battery is fully charged.

I bought a brand new gel battery. I charged it fully and the bike fires right up and runs like a dream. I shut it off, put the tender and extension cord away and then it just cranks great but won't start. I checked the voltage and it's 12v. I hooked the tender to it and left it on until the green light comes on. Then it fires right up. I'm lost. I'm afraid to take the bike out because if I shut it off or stall it I will be stranded. Where should I start?

 

A fully charge battery at rest should be 13.8 V, not 12. Hook up voltmeter to the battery terminals. You should see ~14.8V at 2000 RMP; if not then the battery isn't being charged. Possible culprits: alternator brushes worn past the service limit, voltage drop due to corrosion at the electrical connectors, faulty voltage regulator.

 

I will check that out today. Beautiful day for a ride. Thank you for the quick
response.

 

It could also be a gummed-up starter drawing so much current that it won't leave enough juice to fire the bike unless the battery is fully charged.

Try going for a SHORT ride that ends up back home; remember that it's not charging until above 2200rpm or so.

Are you sure that particular gel battery is compatible with the bike's rather primitive electrical system? Depending on spec, the bike may not be capable of fully charging it.

 

I have gone through the starter. It was nasty and had a hard time turning the bike over to begin with. It spins real nice now. I got the gel battery through a local Yamaha dealer. So, hopefully they got the right one. It fits fine anyway.

 

I left it on the tender overnight. Voltage around 13v before starting. Fired right up (it's about 90degs here today). While running i get 13.8v. Ran it for a few minutes. Got 14v at 2000rpm when warm. Shut it down and it started right up. After shutting it down I got 13v. I'm letting it sit off the tender and I'll go back and check the voltage and hopefully start it again.