[Ducati Scotty]

Newer bikes or vintage?  I know that there were many bad incidents back in the day connecting 6V bikes to 12V cars.

Scott

[gremlin]

     Every year several customers come in that jump started their bike from a car. Most get away with it. Occasionally I get a big repair bill. I have seen fires, melted wiring, damaged/burned out electronic ignitions and regulator/rectifiers. Hardly seems worth it. You can safely jump it off another bike or small battery.

And, to what do you attribute the damages ?  (too many AMPs is self-evident) what caused all those AMPS to flow ?

[Ducati Scotty]

Indeed.  I couldn't see this happening with a modern bike but an older one, well, motorcycle starters weren't always built so well and sitting around for 30+ years probably doesn't make them better.

Scott

[gremlin]

.......motorcycle starters .........

I SEE !   said the (formerly) blind man ......

[barenekd]

Rich, learn to push start it.  Key on, ignition on, put it in second gear and pull in the clutch.  Now get it moving: roll down a hill, push from a friend, or push next to it.  Once it's rolling get on the seat and let the clutch out gently.  The turning wheel will force the engine to turn and should get it started.  As soon as it starts pull in the clutch and give it a little gas to get rolling.

This is all fine to a point. When you've jumped on the bike and are ready to drop the clutch, stand up and drop your butt on the seat  as you drop the clutch.
If you don't, chances are real good that the rear wheel will just lock up! Then you have to start over and do it all again!
This was a starting technique used by road racers in the old days. (that's before the '80s). They called it bump starting. As the rider came to the starting grid, he'd put the bike in second gear and then back the bike up so the piston was backed up against compression. If the bike had a manual compression release, he could use that to unload the cylinder. Two strokes didn't generally have this option. This gave the piston some free movement when the rider started pushing. When the flag dropped the riders started pushing there bikes. they usually only took 3 or four steps and jumped on side saddle and popped the clutch as they hit the seat. The bikes hopefully started, and they got on properly. If it didn't start, they were in a position to get off and continue pushing.
Had a lot to do with why I never got into road racing, until much later!
Bare

[kammersangerin]

All helpful because I brought my bike home but due to a nasty infection haven't been able to get it off the truck. The weather was just to yucky. Now after being in the cold all these nights, I hope it fires. It was stored for a month while I was gone, and I don't know if they fully charged the battery or not. I will say my Vespa is very good about starting after sitting in the cold for several days. As in touch the starter start.

[barenekd]

It basically comes down to how good a battery do you have. My bike sat for a few weeks several times usually when I was working on it and even using battery power and it never needed to be charged. Still started the bike up straightaway.
A good AGV kinda takes the worry outa that crap!
Bare

[Rich Mintz]

OK, here's a related question:

I'm now plugging into the Battery Tender whenever I'm in the garage. Today I took the bike right off the Battery Tender and went for a 12-mile round-trip (with a stop in the middle for lunch). When I got back to the garage and plugged in, the red light lit up (meaning: charging; less than 80% full). In a couple hours the blinking green light (80%+) will go on, and then eventually later today it'll be solid green (100%).

Is this normal -- that is, is it normal that after starting up the bike and riding 12 miles, the battery is "less than 80% full"?

[Gypsyjon]

My G5 has a gel battery but often will not turn the engine over if it has been sitting for a week or so. With the bike in neutral, pulling in the clutch seems to take enough weight off for it to turn over and start.

[gremlin]

OK, here's a related question:
..........is it normal that after starting up the bike and riding 12 miles, the battery is "less than 80% full"?

excellent question.   
short answer = no, but, kinda yes.

slightly longer answer:
batteries charge to 67% very fast, then, they charge 67% further (89%) quite a bit slower (10 times as long) the final 10% charge is rarely provided by vehicles except on cross-country excursions.

free advice:
to avoid overcharging your battery, give it time to cool down to room temperature before you connect it to consumer-grade battery tenders.
 

[Gypsyjon]

excellent question.   
short answer = no, but, kinda yes.

slightly longer answer:
batteries charge to 67% very fast, then, they charge 67% further (89%) quite a bit slower (10 times as long) the final 10% charge is rarely provided by vehicles except on cross-country excursions.

free advice:
to avoid overcharging your battery, give it time to cool down to room temperature before you connect it to consumer-grade battery tenders.
 

Gremlin, why is that? i.e to let battery cool off before putting on charger?

[gremlin]

Gremlin, why is that? i.e to let battery cool off before putting on charger?

".....battery voltage shifts with temperature. Warmer surroundings require slightly lower voltage thresholds and a cold ambient prefers a higher level. Chargers exposed to temperature fluctuations should include temperature sensors to adjust the charge voltage for optimum charge efficiency. If this is not possible, it is better to choose a lower voltage for safety reasons...."

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

[Royalista]

Under normal conditions a battery needs a ride of about 12 miles to recharge the loss through starting. Given the fact that you stopped for lunch, your ride of 12 miles (in winter city traffic?) with 2 start ups would drop the battery close to or just below the 80% mark.
If my math at this hour is still reliable that is. 

[Rich Mintz]

Thanks Gremlin and Royalista.

For whatever it's worth, 4 hours later the Battery Tender was showing "fully charged." So I won't read more precision from the blinking lights than is appropriate.

[Ducati Scotty]

Rich, do you have the stock headlight or the 7"?

Scott