Dead Battery - Performance Loss?? - Wrist Twisters
 
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post #1 of 7 Old 08-19-2008, 01:00 PM Thread Starter
 
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Question Dead Battery - Performance Loss??

Can someone explain to me why a dead battery (about 12% charge) would cause a bike with a Constant Velocity Carburetor (an '07 VT600CD in this case) to misfire/backfire after being bump started?

A buddy of mine called me yesterday for some help getting his VLX started after draining the battery. We were able to get it running easily enough even though neither of us had ever bump started a bike before, but it barely made it back to my place, putting along and backfiring the whole way. I assumed that there would be other issues he would have to address after his battery was recharged, but I fired it up this morning after disconnecting the charger and it seems to idle and rev normally in neutral . What's the deal? Are CV Carbs controlled by some sort of ECU? Is there something more that he should be concerned about now that the battery is recharged? I don't get it...

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post #2 of 7 Old 08-19-2008, 01:01 PM
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Not enough juice for the ignition most likely.

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post #3 of 7 Old 08-19-2008, 01:12 PM
 
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Quote:
Originally Posted by justintyme73 View Post
Not enough juice for the ignition most likely.
Low voltage = low spark , simply put .

Alot of bikes need a certian voltage to power the ignition system , if you dont get that voltage, the coils/ignition system arent working correctly, even if you get the bike running and chanrging, its still working from a deficit.I dont rember alot about this bike, but, this holds true for most of the CDi ignitions -What was your voltage ? Did it pick up after having it running for a while ? You may need ot get a new battery if it didnt hold that charge that running should have put into it .

The way your describing, it woulsds like this bike has been sitting for a bit. Are you sure the problem isnt crud in the carbs ? it doesnt take much time at all for fuel to go bad -

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post #4 of 7 Old 08-20-2008, 09:46 AM
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i think 2ohno explained it well. the alternater should have put out enuf juice to take care of that. if it didnt i would look at the alt to. hook up a meater to the cabels with the bike running but not connected to the bat, let us know what you get.

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post #5 of 7 Old 08-21-2008, 09:11 AM Thread Starter
 
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Better Understanding

It's been a couple of days now, and he's been running it with no problems, so the misfires were definitely being caused by the insufficient voltage. I didn't fully understand the part the battery plays in the ignition system I guess. Thanks for giving me the information/keywords I needed to do some further research.

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post #6 of 7 Old 08-21-2008, 09:14 AM
 
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Just found this - Should have put it up rather than subjecting you to my horrible typing -

Its from this site - http://www.dansmc.com/cdiignition.htm

Most Dirt bikes are a CDI magneto, and do not require a battery. Most street bikes are a battery charged CDI, and need a fully charged battery. That battery also has to run the starter, lights, radio, and other stuff in addition to the ignition. Different things require different power requirements from the battery. We think of the battery as supplying a steady 12 volts and it should. But, things can vary. What does all this have to do with electronic ignition ? Most electronic ignitions require a full 12 volts to give out a good spark. If you let the bike sit a long time or the battery is weak, you may not get a full 12 volts. Now the starter may spin just fine, but the starter requires amps more than volts. Think of it like this. Amps are volume, volts are pressure. Amps won't jump a spark plug gap and volts won't spin that starter. At least they won't in the numbers that we deal with. Anyway, the starter is spinning but the ignition is not getting enough volts to fire the spark plug. The moral ? Make sure you have a good, fully charged battery in the machine before you start hunting for ignition problems.

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post #7 of 7 Old 08-21-2008, 09:19 AM Thread Starter
 
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Quote:
Originally Posted by 2ohno View Post
That's exactly the page I found once I knew what to look for. Thanks again.

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