My bike just quit on me! Please help!

[sb750]

So I got my 1978 cb750f last week and it has been running great. Had the last couple days off so I went over everything tuning it up. New plugs, new oil, new oil filter, cam chain adjustment, valve adjustment. The wife and I were off today so we decided to take the freshly tuned cb for a cruise around Santa Barbara.

We cruised around a bit and stopped by the ocean, bike was running great. Went to get back on and I noticed that the neutral and oil pressure light did not come on when I turned the key. Pushed the starter and nothing. Pulled the side cover and wiggled the fuses a bit (I have zero electrical experience and no clue how to tell if one is bad) and bam the lights came on. Tried the starter, it cranked but barely, like a low battery, so I kicked it over and it fired right up. We were back on the road. Cruised a bit more to try to charge up the battery, we were driving along slowly no problems what so ever and the bike just died on me. This time the neutral and oil lights were still on but the electric Start wouldn't do anything. Tried to kick start it and nothing. Made sure there was plenty of gas in the tank. Let it sit, tried to kick start it some more and nothing. Electric start won't do anything. Tried to play with the fuses some more. I can't get it to start for anything!

I have no idea what to do, and what to start checking!

Could a bad battery be causing this? Bad fuses? Even if the battery is dead shouldn't it still kick start?

Please help a newb figure out what to do and what to try

 

[grepper]

>Could a bad battery be causing this?
Yes

>Even if the battery is dead shouldn't it still kick start?
No


These bikes don't have a permanent magnet alternators, they need electricity to start charging and you need power to the coils to get it running. Some coils will fire with very low power and you'll be able to kick it over.

Could be a short, loose fuse or something like that too. Could be real simple, like a loose battery connection.

First fully charge your battery. Then get it running, at idle you should be around 12 volts, then at 3 or 4 K it should be about 14 volts. If the volts are not going up as you rev it, it's not charging. If it is, possible your battery is bad and not holding a charge. You can take it to an auto parts store and they can test it, just like a car battery.

If it's not charging, then it could be a few things. There's trouble shooting guides online for troubling shooting charging problems so you can narrow down what's broken so you don't end up replacing parts unnecessarily.

 

[sb750]

Thanks grepper. I have the battery on a charger now so I will let you know if that gets it running. To check and see if the volts are going up do I just buy a voltmeter and hook it up to the battery connections?

 

[Stabler]

Yes. While idling and then revving.

 

[grepper]

Yeah, I have been using one of these http://www.harborfreight.com/7-function-multimeter-98025.html cheap multimeters from Harbor Freight for years. They work just fine for the weekend tinkerer.

 

[sb750]

Put the battery on the charger last night and bike on the bike this morning and it fired right up no problem! Thanks for the direction guys. I'm gonna pick up a multimeter after work and I'll let you know the results with that. I'm thinking after working in the bike the last few days without ever giving the battery a chance to charge back up. Then cruising around town at lower Rpms u may have just ran the battery down to nothing. Well it's back alive and I'm learning more and more about this bike every day and loving it all! Thanks so much for the guidance

 

[motogtp]

You may also want to check the fuses to see if they get hot when running. I had a main fuse that did not blow but I saw a little ball of solder inside. It got hot! After I cleaned and scraped the terminal holders I never had a problem.