1973 GT250 K Charging issues

[Aussieads32]

Gents,

I have a 1973 GT250k i have just finished rebuilding, this is the model without the regular only the rectifier. When i increase the revs to 5000rpm the charge does not pick up. In the end the battery goes flat and the bike shuts down.

I have tested the rectifier its not shorted. The alternator is producing AC current something is not right...... This is the model also when you turn the head light on its ment to increase the charge also.

I have checked everything and i am at a utter loss.

Can anyone help or have photos of how yours is hooked up if you own a 73 gt250 to see if i am on the right track.....

Cheers Ads

[Craig380]

Hi and welcome!

Before doing anything else, I would do a voltage drop test on the main earth wire and earth connection for the battery.

Connect the red lead on your multimeter to the battery NEGATIVE and the black lead to the earth wire terminal where it meets the frame. Then with the engine kill switch OFF, turn on the ignition. If you see more than about 20 millivolts on the meter, either the earthing point needs cleaning or your earth wire is bad at the crimped ends, or somewhere in the wire itself.

You can also run another length of wire from the battery negative to a clean earth point on the frame and see if that reduces the multimeter reading.

[Aussieads32]

Hi,

03.7 milli volts is the reading I get. The first the I did was clean up all the earths and clean the contacts. Loosing my mind slowly......

Ads

[jabcb]

The light on/off switch also adjusts the alternator output -- you may have a problem in that circuit.

With a fully charged battery, check the voltage @ 5,000 rpm with the lights on & the lights off.

[Aussieads32]

Hi,

Yep been over all that only getting a minor increase at 5000 rpm like .50 of a volt if I am lucky, lights on off the whole bit.....

Taken some videos and pictures resistance on the rectifier was high.... Around 12

Ads

[smokin_blue]

It has been several years since I sold my GT250 but here are a couple of issues I saw or have seen on other models.

On my 250 I once had the same issue and it was because the rectifier plate that should be isolated in the air was touching the battery box (understand this was on a custom so placement might be different) but the key was the box was grounded which shorted the rectifier to ground and killed all charging.

Second item, you state the rectifier is not shorted. When you checked the rectifier did you check it out of the circuit? if so you should be able to check the 3 combinations across the diodes with an ohm meter. you should have a reading one direct but NOT the other (meaning flip the probes). If a diode goes out you get flow going both ways through that leg and your charging is shot.

I have experienced this with my 79 GS750 and now about 2 weeks ago on my 2006 Triumph. (gotta thank the big man upstairs that, that one died only 1/2 mile from home at the end of a 150 mile ride)

[Aussieads32]

Gents

Progress I changed out the stator and magneto, I get 14 volts, when I turn the headlight on the colts Jump around and the diode gets red hot.

Any thoughts ?

I know the K model does not have a reg so should I add one ?

Ads

[smokin_blue]

so it sounds like something with the rectifier if that is getting that hot. have you check the diodes for one direction electrical flow (or continuity)?

[Aussieads32]

Yep

Taking the parth of least resistance and ordered a new regulator / rectifier going to fit that keep
That charging system seperate the loom and just tap some power for blinkers and lights.

Not messing around with the turning the head light on engaging the third part for night time charging just going to run it 24/7 and regulate it.

Seems a lot of guys take this course with this K model.....