Topic: 76 CB750 hard starting. Battery drains in 10 seconds!

[redjet]

When I got this bike 6 months ago, it would fire right up when I pressed the ignition button and ran smoothly. This bike came to me with Dyna S ignition and coils already installed but rest of electrical system was shot.

Installed:
New wiring harness
New regulater/rectifier
Blade fusebox from Hondaman
New starter solenoid
New battery

     Its now 6 months later and she's ready to start. Hit the ignition button and she fire right up! Runs smoothly for about 20 seconds and dies. Try to restart but cranks for only 10 seconds and battery is dead. Hmmmmm. Recharge battery and try again. Same result. 10 seconds cranking and then drained battery. Ok, recharge battery and put on meter. Yup, full charge. Try to start again. Same result. Drained in 10 seconds. I must have a bad battery.
     Ordered new battery, different brand this time (Yuasa), charged it to max and gave it a shot. Same result. 10seconds of cranking and drained battery. Borrowed friends charger. Recharged battery, checked it on meter to make sure it had full charge and tried again.  This time it turned over only once (really struggling) and I started to smell rubber burning.
     I'm stumped. What could possibly drain a battery in 10 seconds?

[Stev-o]

Could be a short in the wiring, maybe grounding out?  I would go though all of the wiring, obviously something is wrong. 
Good luck.

[thrutheframe]

  Disconnect the battery, disconnect the black wire from both coils, make sure the black wire isn't touching the frame.  Turn the key to the run position and do a continuity test between the frame grounding point and the hot lead of the battery.  If you get nothing, do the same test with the starter button pressed in.  I suspect you'll get continuity between ground and hot on the "pressed in" scenario.  If that is the case you've isolated the problem to either the key switch, starter safety unit, starter relay or the wiring coming back from the start button.  Unplug each unit until the condition goes away.  If you don't get continuity either way try the same test with the battery connected, that will supply power to the relay and send current to the starter.  If you get continuity this way, you know that the problem is the heavy gauge wire past the relay.

Good luck.

[ekpent]

Sure the battery isn't toast ? Take it somewhere for a test to eliminate that variable.Should last longer than 10 seconds after a charge.

[thrutheframe]

Sure the battery isn't toast ? Take it somewhere for a test to eliminate that variable.Should last longer than 10 seconds after a charge.

+1 on that.  Make sure you charge it AND let it rest for 20 or 30 minutes after you charge it.  You may have already fried two good batteries if it's dead shorting to the frame under the high current demand of running the starter motor.

[bollingball]

  Disconnect the battery, disconnect the black wire from both coils, make sure the black wire isn't touching the frame.  Turn the key to the run position and do a continuity test between the frame grounding point and the hot lead of the battery.  If you get nothing, do the same test with the starter button pressed in.  I suspect you'll get continuity between ground and hot on the "pressed in" scenario.  If that is the case you've isolated the problem to either the key switch, starter safety unit, starter relay or the wiring coming back from the start button.  Unplug each unit until the condition goes away.  If you don't get continuity either way try the same test with the battery connected, that will supply power to the relay and send current to the starter.  If you get continuity this way, you know that the problem is the heavy gauge wire past the relay.

The way this is worded.You are saying to do a continuity test with power on. Or am I reading this wrong?

[thrutheframe]

  Disconnect the battery, disconnect the black wire from both coils, make sure the black wire isn't touching the frame.  Turn the key to the run position and do a continuity test between the frame grounding point and the hot lead of the battery.  If you get nothing, do the same test with the starter button pressed in.  I suspect you'll get continuity between ground and hot on the "pressed in" scenario.  If that is the case you've isolated the problem to either the key switch, starter safety unit, starter relay or the wiring coming back from the start button.  Unplug each unit until the condition goes away.  If you don't get continuity either way try the same test with the battery connected, that will supply power to the relay and send current to the starter.  If you get continuity this way, you know that the problem is the heavy gauge wire past the relay.

The way this is worded.You are saying to do a continuity test with power on. Or am I reading this wrong?

yep.  you are right... bad idea wasnt thinking

  Disconnect the battery, disconnect the black wire from both coils, make sure the black wire isn't touching the frame.  Turn the key to the run position and do a continuity test between the frame grounding point and the hot lead of the battery.  If you get nothing, do the same test with the starter button pressed in.  I suspect you'll get continuity between ground and hot on the "pressed in" scenario.  If that is the case you've isolated the problem to either the key switch, starter safety unit, starter relay or the wiring coming back from the start button.  Unplug each unit until the condition goes away.  If you don't get continuity either way try the same test with the battery connected, that will supply power to the relay and send current to the starter.  If you get continuity this way, you know that the problem is the heavy gauge wire past the relay.

The way this is worded.You are saying to do a continuity test with power on. Or am I reading this wrong?

yep
You're right BAD IDEA  I wasn't thinking.  This will toast you meter.