GT750 - Battery required?

73buffalo · Post by **73buffalo** » Tue Nov 04, 2008 9:23 am

I recently acquired a 1973 GT750 K. I was working on the turn signals and the battery was weak. I kick started the bike and was running with lights on, testing signals, ect, and the bike died. Felt like I lost spark. Lights were really dim. I took the battery out to charge, and the bike would not fire up at all. Fully charged battery and the bike runs fine again. Is the battery required to run this bike, or is there something wrong with my charging/ignition system?

TLRam1 · Post by **TLRam1** » Tue Nov 04, 2008 9:34 am

I think the battery is required and the charging system can not overcome your weak battery. It is on my GT380 and it does need to be in pretty good shape.

tz375 · Post by **tz375** » Tue Nov 04, 2008 10:16 am

terry is spot on. The charging system on a GT750 uses the battery to create a magnetic field in the alternator. It doesn't have permanent magnets.

So without a good battery, no charge.

73buffalo · Post by **73buffalo** » Tue Nov 04, 2008 10:22 am

Thanks for the quick responses. Glad to know its not something else that needs repair/replace. Makes the kick start seem a little pointless though...

jeff g · Post by **jeff g** » Mon Nov 24, 2008 6:30 pm

73buffalo wrote:Thanks for the quick responses. Glad to know its not something else that needs repair/replace. Makes the kick start seem a little pointless though...

Not really. The GT's really like fully charged batteries and need 10+ volts to fire the points. If the battery is weak and you try the electric start, the motor may spin, but the battery voltage drops too much to fire the points.

Here's a tip to help see if you need to kick start your bike. Turn the key to "on" and check your headlight. If it's dim, turn off the light and kick start. If it's really dim, put the battery on charge.

Coyote · Post by **Coyote** » Tue Nov 25, 2008 8:03 am

+1

These old bikes had what is commonly referred to as a battery excited ignition. If the battery is low or weak, the engine will perform like crap. If your battery is old and doesn't seem to hold a good charge, replace it. The difference is worth the price.
To check your charging system you will need a volt meter. If you don't have one, borrow one. Set it to DC volts and fire up the bike. Apply the probes to the battery terminals, with the red lead on the + side. You should see about 12 volts at idle. Now rev the engine some while watching the meter. As you get to around 3 grand you should see around 13 volts. As high as 13.6 at 4 grand plus. If the readings are similar, your charging system is working. If revving the motor shows no voltage increase, try a different regulator, rectifier and your ground connections. If you see upwards of 15 volts, the system is overcharging and probably the fault of the regulator. Over charging will toast a battery in pretty short order.