Cafe Racer Forum banner

1 - 5 of 5 Posts

·
Registered
Joined
·
5 Posts
Discussion Starter #1
I am a new member but have been reading on this forum for a while.
I came across an 81 cb750 and picked it up. Now it has some small issues I am slowly working through(haven't got the repair manual yet), but last week my turn signals quit working and today I went out to go for a ride and the battery was dead. I just ran it down the road and popped the clutch fired right up, but I was wondering what a comon reason for a dead battery might be on these bikes. I am not familiar with the charging system on these bike are or where to start. Any help would be appreciated. I guess I should put up some pictures as well but that will come later.
 

·
Registered
Joined
·
23,303 Posts
first off...which model? K, F, or C?

Turn signals could be the flasher, fuse, or bulbs. It could also be a short somewhere in the bike's electrical.

is it a new battery?

Honda's don't break even charge until 2000 rpm (unlike a car which breakeven charges at idle) so you can get a dead battery just from running it under 2000 rpm. Also you could have left the key in the park position (one position past lock) or you have a short that is drawing power.

if you want to be sure it is a short, put a volt meter on it and see if it is discharging over time with the bike off. While you are at it use said volt meter to make sure the charging system is working since these bikes are known to blow stators.
 

·
Registered
Joined
·
5 Posts
Discussion Starter #3
To be honest I am not sure if it is k, f, or c
edit it is an f
That is very helpful though i will check the charging system on it right away, What would the normal voltage be while charging?

I was thinking a short guess I will just have to start going through the wiring. I was more into the newer bikes but decided to learn how to do one myself. Thanks for the advice I am heading to the Driveway again
 

·
Registered
Joined
·
23,303 Posts
at around 2000 rpm (actual rpm will vary but it will be in the 2K range) the charging will be 12v. before that it will be less, after that more. Rev it all the way up an make sure it hits terminal charging at around 14V.
 

·
Registered
Joined
·
2,740 Posts
Before going down the endless road of troubleshooting, check to see if your battery can hold a charge first. These batteries have a bad habit of developing an internal short and eating themselves to death. I usually use the old fashion four beads in an eye-dropper tester and check each cell. Most local auto part stores can check your battery with a much more expensive test gear - and while your there, they'd be happy to sell you another battery.
 
1 - 5 of 5 Posts
Top