Is it my alternator or my reg rect?


Active Member
Got my bike running this week fir the first time and took it for a spin. I had a new battery in it fully charged it measured about 12.9 V. After a few mins it died and would not start up again. I recharged the battery which had depleted to about 11.5V put it bavk in and did the standard tests while revving the bike to 5k the battery did not read over 12.9V I then unplugged my alternator cables and checked them. They did not read over 75V that the manual states. So I am quite sure the problem is my alternator. But how can I be sure my reg rect isnt also gone? Cheers. I jave a 1981 suzuki gsx250 and this is my first build.

Sent from my GT-I9300 using Tapatalk 2
75v AC is MORE then enough from the alternator. What does the meter read on the battery terminals @5000rpm?

Tape the meter to the tank and take her for a spin ;)
Ok I think I have diagnosed my problem. The battery was reading 12.8v whike running at 5k and so I pulled off the alternator cover and about 10oz of oil spilled out. Im not sure if its supposed to have oil behind that cover but once I gave every thing a wipe down and put the xover back on I fired her up and was getting good voltage from the alternator terminals and also around 13.5v on the battery at 5000rpm. So now I nees to figure out if there is supposed to be oil there and if not where is it coming from?

Sent from my GT-I9300 using Tapatalk 2
Ok still not sure. Apparently the alternator on this bike is supposed to run wet. It helps with cooling. So I got it running again and tested volts on battery and again 13.5 ish so I took her for a spin and after 5 mins she was sounding like she was going to cut out and then all of a sudden nothing. Tried to push start it but didnt want to go. Not sure what my issue is here?

Sent from my GT-I9300 using Tapatalk 2
I had a similar problem with my charging system as well. Check the ground wire of the regulator and be sure it's properly grounded, that fixed my problem. Also the book should have a series of tests for you to check weather its good or bad.
If you go here...
*Edit: you would be lost, I misdirected you thinking Honda CB... sorry*

12.6 is you battery voltage. Apperently during you test ride, the charging system quite working and the engine depleated the battery until it could no longer run. Then on your way home, without the load from your engines electrical system the battery recovered.
Ok so I walked down today with a charged battery and some new oil. Checked the oil level. It was low but not empty. So I put more oil in. Plugged in the battery tried to fire her up but no prevail. The starter was going but she wouldn't fire up? The motor still turns. I had pretty dodgy leads that I thought I may have fixed but it is possible that maybe they have come loose. I am waiting for my nate to come over now to help me push it home as it just so happened to die about half a km down hill from my house.
And bert. Are there any tests I can do to see if I did any damage to my engine? Thanks guys. Again my first build so its a steep learning curve

Sent from my GT-I9300 using Tapatalk 2
If you have an oil pressure gauge, all Suzuki four strokes have a take off point.
If oil was only down to lower level everything should be fine
What have you done to carbs?
Bert, 75v is no load AC voltage, not sure if tests were done properly.
It would probably be better to do continuity tests first
i'm sorry i can not help you any further as i have not enough knowledge of suzuki's. Good luck! I'm sure another member will give you the answer, or even better, you'll find it out yourself!
crazypj said:
It would probably be better to do continuity tests first


...and, whatever the problem turns out to be, it's a good idea to eliminate the NipponDenko R/R this bike started out with, in favor of a more reliable Shindegen. The GS Resources has a comprehensive list of compatible R/R's.
Suzuki's tend to have real crappy reg/rec, I usually fit Honda CB400t ones (even brand new GSXR, at least until 2011)
You have a permanent magnet alternator so it's a pretty easy swap
Top Bottom