Topic: CB 750 : Was running fine, now its not??? Help!

[91greg325i]

I just had some work done on my 79 cb750 10th anniversary edition. I know this is a DOHC, but I figured someone here may be able to help me find out whats wrong. I had the Carburetors rebuilt as well as the electrical connections cleaned up. After that it was running great for a few days, but then started having trouble. It would simply start and die unless I kept it above ~2000 RPM. I've searched on here, and the charging system seems to be a common problem. What exactly would the likely problem be. I'm at wits end and I'm hoping someone here can provide some much needed advice!

Thanks in advance!

Greg

[the technological J]

are we to assume that you have done all the tuning? is the bike properly tuned are the carbs synched?are all of your exaust pipes the same temp? i would check into your 3000 mile tune-up and sunch the carbs and see if you have better luck

[91greg325i]

Yes, they were tuned after being rebuilt. And I don't have an infrared temp. sensor, but it is definitely firing on all four. The thing that leads me to believe charging, is that it was fine for a few days (battery was charged). Now that it has to be kept above 2000 to run, maybe the battery is low and the charging system is too inadequate for the battery? Again, I'm not really sure about the charging system being the culprit, it just seems that it is for so many other people. What exactly causes the drain on the battery @ low RPMs? I want to get her running again!!! 

[ev0lve]

Again, I'm not really sure about the charging system being the culprit, it just seems that it is for so many other people.

Easy enough to get a multimeter and find out for sure?

[the technological J]

you should unplug and replug all your connections make sure its nice and tight...  u might have a short also..... but focus and eliminate one prob at a time... did u have a charging issue before this prob?

[91greg325i]

Again, I'm not really sure about the charging system being the culprit, it just seems that it is for so many other people.

Easy enough to get a multimeter and find out for sure?

Well, Ive never had charging issues before, so I'm not sure what to do when I get the multimeter from a friend (i.e. where to hook it up, what to read, etc.). I know, I'm a noob when it comes to electronics, so forgive me if the answer to you seems simple. Thanks for all of the replies so far!

[ev0lve]

I'm still a noob myself  Just take the leads to the battery and find out what it's reading volts/amps - then run the bike and note the change. If the battery is less than 12.x volts with the bike not running that's a clue. If it's 12v, you turn the key and it's less with the headlight off that'll be a clue as well - and so on with the bike running at various RPM

[91greg325i]

I'm still a noob myself  Just take the leads to the battery and find out what it's reading volts/amps - then run the bike and note the change. If the battery is less than 12.x volts with the bike not running that's a clue. If it's 12v, you turn the key and it's less with the headlight off that'll be a clue as well - and so on with the bike running at various RPM

Thanks, thats a big help! I'll see if my friend can come over sometime soon and hopefully we can get to the bottom of this.