Topic: Bike Died, No Power!

[NewOldSchool]

My 1974 CB750 is my daily transportation. I've owned it about two years and it has never let me down until today. I maintain it religiously and never miss an adjustment or oil change. Its allllllmost at 30,000 original miles and today she let me down!

I have been riding it back and forth to work daily and round trip 70 miles a week. A little back story, I usually only use the high beam on the freeway because I know the old charging system has a weak reputation and I've put a modern Bosch headlight in it. My thinking is that the charging system can better cope with the high beam at sustained high rpm.

So tonight I hop on the freeway to head over to the west side to see my girlfriend and its running fine. (Ran fine all day doing errands) I flip on the high beam and the bike kind of bogs when I go to pass. It then begins to cut out a bit, so I flip it to low beam only. It runs ok for a moment, then begins to die again. I get off the freeway and when I come to a stop it dies. I turn the lights off and it will kick start (electric start wont work at this time) and stay running, but only above 3000 rpm.

I limp to a friends house with the lights off, which is quite an adventure at night in a large city.... and I pull the battery. We test it and it reads 11.36 volts with his multi tester. What gives??? Is it the voltage regulator, am I not charging, is it the battery, how do I test this?

HELP!?

[Duke McDukiedook]

How old is the battery?

[NewOldSchool]

About a year and a half. I have refilled it with distilled water once about 5 months ago when it was very low on electrolyte.

[TwoTired]

Fully charge the battery with an off-the-bike charger.  Let it rest unconnected for two hours after charging and measure the battery voltage; 12.6-12.8V is ok.
You could also take the battery to a shop to have it load tested, in order to see if it is still serviceable.

Anyway, put a known good battery back in the bike with lighting off and measure the voltage at idle, 2000, 3000, 4000, and 5000, RPM.  Record these readings.
Repeat the above test with the lights on.

Report your findings to us and we will give you the next steps toward finding the problem.

Of course there is the alternate method of replacing each part of the charging system in turn, until it no longer runs the battery down.  But, I prefer testing to find THE bad component and replacing just that.

You could also tells us what the wattage of your replacement headlight is.  The bike's alternator is not an unlimited source of power, even in pristine condition.

Cheers,

[bollingball]

I usually only use the high beam on the freeway because I know the old charging system has a weak reputation and I've put a modern Bosch headlight in it. My thinking is that the charging system can better cope with the high beam at sustained high rpm.

This makes no sense at all. Can you explain you logic of increasing the load to help your weak charging system 
Ken

[Duke McDukiedook]

Yeah, high beam on H4's are usually 60 watts compared to 50watts for low beam.

Nomakeadesensea.

If you burned off all or a good amount of your electrolyte you might have snicklefritzed some or all of the cells.

[iron_worker]

I had the same problem. I replaced my rectifier/regulator and it turns out it was just a super corroded/melted terminal inside one of the connections.

Check the inside of the white block connectors going to the reg/rect.

There are also instructions out there on how to test the function of each and also how to test the alternator itself.

But I agree, start with a fully charged battery and do the tests as mentioned.

Good luck.

IW

[Rgconner]

Just spent some time replacing a 12 inch red wire in the wiring harness. Engine would cut out just like I hit the kill switch. Headlight is much brighter at idle now as well.


It is time to start going through the harness down by the fuses/regulator and start cleaning things us. Test wires with an ohm meter. If it changes resistance as you flex it, it has broken internal copper strands.


Check and clean grounding connections. They corrode/vibrate loose and you will lose a lot of voltage there.

Check and clean the contacts on the switch. Mine dropped the voltage 4 to 5 volts. Teardown and cleaning of the contacts got that back up to proper voltages.

Look at a phillips eco bulbs. They draw 20% less wattage for a standard halogen H4, putting it much closer to the stock wattage.

http://www.amazon.com/Philips-9003-EcoVision-Headlight-Bulb/dp/B00480KPDA

 

[NewOldSchool]

I usually only use the high beam on the freeway because I know the old charging system has a weak reputation and I've put a modern Bosch headlight in it. My thinking is that the charging system can better cope with the high beam at sustained high rpm.

This makes no sense at all. Can you explain you logic of increasing the load to help your weak charging system 
Ken

Pardon my ignorance then, but I assumed more RPM = more wattage...

Yeah, high beam on H4's are usually 60 watts compared to 50watts for low beam.

Nomakeadesensea.

If you burned off all or a good amount of your electrolyte you might have snicklefritzed some or all of the cells.

I am bringing my battery to a dealer buddy to have it load tested this afternoon. While this is being done I will be going over any lose connections as this is usually the first problem and easiest to solve.

Fully charge the battery with an off-the-bike charger.  Let it rest unconnected for two hours after charging and measure the battery voltage; 12.6-12.8V is ok.
You could also take the battery to a shop to have it load tested, in order to see if it is still serviceable.

Anyway, put a known good battery back in the bike with lighting off and measure the voltage at idle, 2000, 3000, 4000, and 5000, RPM.  Record these readings.
Repeat the above test with the lights on.

Report your findings to us and we will give you the next steps toward finding the problem.

Of course there is the alternate method of replacing each part of the charging system in turn, until it no longer runs the battery down.  But, I prefer testing to find THE bad component and replacing just that.

You could also tells us what the wattage of your replacement headlight is.  The bike's alternator is not an unlimited source of power, even in pristine condition.

Cheers,

Will do! Soon as I eliminate the battery and/or simple loose connections as the source of the problem.


Thanks all! I will keep you posted!

[NewOldSchool]

I had the battery load tested at the local shop, then left on a charger all night. It passed as still being "good" according to the very experienced tech.

I brought it home and let it sit for about 4 hours after being taken off the charger. It read 12.05 volts with my meter. I installed it in the bike and it started right up. Ran it for about 5-10 minutes to fully warm it up (did not turn headlight on) and then turned it off.

I took a voltage reading again and the battery had dropped to 11.85 volts. So it definitely isn't charging. I will go through the charging system checks recommended above and report back!

[Rgconner]

If it was fully charged, then 4 hrs off the charger and dropping to 12.05, not 12.5ish, out of the bike means you are losing it internal to the battery.

So it has a short.

See if it continues to lose voltage while sitting unattached, that is how you can confirm.

[TwoTired]

I brought it home and let it sit for about 4 hours after being taken off the charger. It read 12.05 volts with my meter.

That is not a good reading. If it was left unconnected during that 4 hours, you have not proven the battery is good.  In fact, it shows rapid self discharge characteristics.

I installed it in the bike and it started right up. Ran it for about 5-10 minutes to fully warm it up (did not turn headlight on) and then turned it off.

Was it idling all that time?  (Without a fan on the cooling fins?)

I took a voltage reading again and the battery had dropped to 11.85 volts.

This bike will slowly discharge the battery while idling, and only charge the battery (slowly) above 2000 RPM.

So it definitely isn't charging. I will go through the charging system checks recommended above and report back!

Not at idle; normal, its those other checks to tell if it is doing anything.  But so far, your battery is suspect.  And, there is no definite data about the charging system.

Cheers,

[bollingball]

Quote from: bollingball on May 11, 2012, 05:44:32 am
I usually only use the high beam on the freeway because I know the old charging system has a weak reputation and I've put a modern Bosch headlight in it. My thinking is that the charging system can better cope with the high beam at sustained high rpm.

This makes no sense at all. Can you explain you logic of increasing the load to help your weak charging system   
Ken

Pardon my ignorance then, but I assumed more RPM = more wattage...

I don't think you understood me. You are talking about increasing RPM and you are correct under normal conditions increasing rpms will increase the voltage. What I was referring to in your post about using your high beams you are increasing the load or using more power What you want to do is decrease the load by using the low beam or no lights at all.

I took a voltage reading again and the battery had dropped to 11.85 volts. So it definitely isn't charging. I will go through the charging system checks recommended above and report back!

As others have said this in no way tells you it is not charging because it will not charge below about 2k rpms.

For under $10.00 you can get a hydrometer the small one for bikes.that has 4 or 5 balls that float. I think with that you will find a weak cell. WallMart has them in the auto section there are better ones but that one will do. If you end up buying a battery I highly recommend a AGM. Scorpion or Yuasa are two of the better ones.

Ken

[NewOldSchool]

Quote from: bollingball on May 11, 2012, 05:44:32 am
I usually only use the high beam on the freeway because I know the old charging system has a weak reputation and I've put a modern Bosch headlight in it. My thinking is that the charging system can better cope with the high beam at sustained high rpm.

This makes no sense at all. Can you explain you logic of increasing the load to help your weak charging system   
Ken

Pardon my ignorance then, but I assumed more RPM = more wattage...

I don't think you understood me. You are talking about increasing RPM and you are correct under normal conditions increasing rpms will increase the voltage. What I was referring to in your post about using your high beams you are increasing the load or using more power What you want to do is decrease the load by using the low beam or no lights at all.

I took a voltage reading again and the battery had dropped to 11.85 volts. So it definitely isn't charging. I will go through the charging system checks recommended above and report back!

As others have said this in no way tells you it is not charging because it will not charge below about 2k rpms.

For under $10.00 you can get a hydrometer the small one for bikes.that has 4 or 5 balls that float. I think with that you will find a weak cell. WallMart has them in the auto section there are better ones but that one will do. If you end up buying a battery I highly recommend a AGM. Scorpion or Yuasa are two of the better ones.

Ken

I appreciate your advice Ken! I was not clear, I did not let it idle for 10 min, I went on a 10ish minute ride around my city, major streets, varied riding almost constantly between 3 and 5000 rpm.

To elaborate on my High beam usage habits.... while riding at night, I use low beam around town and once on the freeway, with constant high rpm, I will use high beams as it was my reasoning that cruising around at 2-3k rpm with high beams on will really tax the battery. Where as freeway riding at a constant 5000rpm will easily keep the battery replenished.

[NewOldSchool]

I brought it home and let it sit for about 4 hours after being taken off the charger. It read 12.05 volts with my meter.

That is not a good reading. If it was left unconnected during that 4 hours, you have not proven the battery is good.  In fact, it shows rapid self discharge characteristics.

I installed it in the bike and it started right up. Ran it for about 5-10 minutes to fully warm it up (did not turn headlight on) and then turned it off.

Was it idling all that time?  (Without a fan on the cooling fins?)

I took a voltage reading again and the battery had dropped to 11.85 volts.

This bike will slowly discharge the battery while idling, and only charge the battery (slowly) above 2000 RPM.

So it definitely isn't charging. I will go through the charging system checks recommended above and report back!

Not at idle; normal, its those other checks to tell if it is doing anything.  But so far, your battery is suspect.  And, there is no definite data about the charging system.

Cheers,

Sorry I was not clear, I let it warm up for a moment then rode around town, varying rpm between 3 and 5k. The lights were off while doing so and the ride was maybe 5 or 6 miles. Probably closer to 15 or minutes or so. I understand that it is not good to let an air cooled motorcycle sit and idle for long periods of time, and I did not expect the battery to charge while idling.

Thanks for your advice, I will try and source a battery which is known to be good. I took my tech's word as truth when he told me he tested the battery at his shop and found it to still be in good condition.

From what I am being told by you and others the battery is still absolutely suspect.

[NewOldSchool]

FIXED!

So I recharged the battery, and while doing so I began to unplug and blast out all the connectors with contact cleaner. It was going smoothly until I got to the connector for the rectifier. It WOULD NOT BUDGE. I eventually was able to leverage it out with a screwdriver and noticed why it would come unconnected.

The connection where the green wires meet at the plug had melted quite a bit and was very corroded. I had already ordered a rectifier from Oregon Motorcycle Parts because I was getting some strange (I'm sitting at my computer and do not remember specific numbers) readings from the rectifier with my voltage tester.

I cleaned up the connection as best I could and popped in the new rectifier (the green wire on the old rectifier was actually split open and very dirty/greasy in two places near the plug and near the rectifier plate) The bike now charges at a little over 14.5 volts and then drops back down when revved over 5000rpm, so its charging properly.

QUESTION: How hot does a rectifier typically get under normal operating conditions?

 After running the bike for 3 or 4 minutes it was too hot to leave a finger on without burning me. I have ordered a new connector for the harness side of the plug from the same guy to alleviate my concerns that there is too much resistance at the plug.

[TwoTired]

It can dissipate about 10-25Watts more or less.  But, it depends on battery state/ lighting selection/ other electrical mods and engine RPM.

Ever grab a 10-25 watt lamp?

Now you know why there is a heat sink on the rectifier. 

Cheers,

[NewOldSchool]

Understood, thanks!