Re: New to forum/CB650 and my first question!

Posted by rich on Sep 30, 2011; 10:27pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/New-to-forum-CB650-and-my-first-question-tp3381249p3383855.html

Now that you've got a good battery you should test your charging system out and make sure it is working properly. If it's not charging it'll run like crap (poor idle, missing, backfiring, high speed cutout) even with a new battery. This often gets people thinking they've got an ignition or fuel problem when it's actually being caused by low voltage.

You'll need a voltmeter to check the charging output. Connect it to the battery, make note of the battery voltage with the key in the off position. It should be 12.5 or maybe even 13 volts since you've got the AGM. If it's anything less, stop and charge your battery (Caution: Don't charge your motorcycle battery at any more than 2amps or you'll ruin it. If your charger doesn't have a 2amp or less setting get another one).

If your battery is fully charged, start the bike and note the voltage with the headlight on high beam and the engine running about 1700 RPM, you should be back up the 12.5 or 13 volts you started with. 1700 RPM is the initial charging point.

Rev the engine up to ~3000 to ~5000 rpm, you should see at least 14 volts at the battery now (14.4 to 14.7 is optimal). If it's over 15 - Stop! You've probably got a bad regulator and you're overcharging your new battery.

If your results are close to the above (13.5 to 14 volts at 5000 RPM) you probably just need to clean all the connections from the A.C. Generator to the regulator / rectifier, battery cables, etc. Heck, even if it's is charging or not charging at all you should clean the connections, you never know...

If it's not charging at all and all the connections are clean and tight, the primary suspect is the generator rotor. Remove the A . C. generator cover and check the resistance between copper rings on the rotor.  There should be more than 3.6 ohms resistance if it's good.  Most of the time when rotors are bad there will be either infinite resistance (completely burnt out) or less than 2 ohms resistance (internally shorted.)

Here's a link to a thread with a picture of the way to connect the leads to the rotor.

If it's not the rotor you can test the other components following the procedures in this write up on checking the charging system from http://www.oregonmotorcycleparts.com/FAQ.html