Suzuki 2 Strokes

I recently completed the restoration on my 1972 T250. After breaking in the rebuilt motor I started to feed it a few more revs and it started blowing bulbs, including that hard to find and expensive headlight. A quick check found unregulated voltage being dumped back into the electrical system. When I bought the bike the silicon rectifier was junk so a bought a new one from Suzuki. Paul Miller sent me a wiring diagram specific to my model year and I rebuilt the harnesses using connectors from Vintage Connections. Everything works fine it just overcharges.
I had a Kawasaki many years ago that had the same problem, but I was broke, so if I had to ride with the headlight on I just did not rev over 3500.
Anyway, I have read about replacing the rectifier with a voltage regulator, I am reluctant to do so because I want to keep it 100% stock but I understand sometimes it is necessary for a little upgrading.

Any help will be greatly appreciated.

Read this thread: 1970 T250 charging issue

Your bike doesn't have a voltage regulator. The battery tries to do this job, softening the higher voltages.

Some "boiling" of the electrolyte water of the battery is typical. Cheap design of the 1970's. If the voltage is really high, your battery could be spent, or perhaps you made an error when you rewired.

As ConnerVT said, the battery is the voltage regulator in the stock setup.
You have to use a conventional battery that you can add water to.
The battery has to be in good shape & have enough water in it, otherwise it can't regulate the voltage sufficiently.

An alternative is to replace the rectifier with a modern rectifier/regulator.
They do a much better job of voltage control so your headlight will last longer & you can switch to a modern maintenance-free or AGM battery.

I switched to a Tympanium rectifier/regulator on my GT250 & T500.
Costs about $50 & can not be seen unless you bend down to look under the seat.


If you decide to stick with the stock setup, check your wiring & the battery.
If everything looks good, then post a pic of the wiring diagram you used.

Let us know if you decide to upgrade to a modern rectifier/regulator & I'll find the posts on wiring them up.

Thank you for you responses.
I am using an AGM battery so that must be part of the issue. After 45 years of riding and numerous instances of battery acid on exhaust and frames I try to avoid wet acid conventional batteries, if possible.

jacab, I believe I would like to install a Tympanium rectifier/regulator. I have attached the wiring diagram provided by Paul Miller, as the one in my service manual apparently was not for my model. If you can, please provide the post on wiring information and if the unit you purchased has given you good service than also the manufacturer and model.

That's a sweet looking T250.


Tympanium is the brand name. Currently available via eBay for $42 including shipping.
http://www.ebay.com/sch/i.html?_from=R4 ... h&_sacat=0

My GT250 is wired up as shown in the maximum output wiring diagram (last of the 3 diagrams):
viewtopic.php?f=29&t=6786&p=121472&hili ... or#p121472

I think I have a pic of the Tympanium installed on my GT250 -- I'll post it if I find it.

Pic of the Tympanium installed on my GT250:


The battery box bolt is a little too big to fit the Tympanium mounting slot.
The Tympanium housing is soft aluminum -- you can easily make a notch with a file to allow the bolt to fit.
You'll also need to get a longer bolt. Make sure its not too long or it will damage your battery.

I want to thank everyone for their help but am still having the same problem.
I installed the Tympanium and wired it in exactly like the recommended drawing and the result was a charging voltage over 20 VDC at 4000 RPM. I reconfigured the wiring to stock, still over 20 VDC at 4000.

jabcb, what kind of battery are you using? Maybe I will be forced to run a wet lead acid.

Thanks again, Geoff

I use an AGM battery.
The Tympanium should limit voltage to around 14.5V

I think you wired up something wrong.
How much of the wiring is original & how much did you wire up?

For now it might be advisable to remove your big-$$$ flat-bottom headlight,
and do all your testing with the lights switched off.

I hope you can see how the wiring is routed. It is the same as the stock rectifier. I tried reconfiguring to the "recommended" setup shown in the link with the same results.
I thought maybe the problem is located somewhere else in the wiring but everything works normally, all lights, warning lights, horn etc. Additionally, I used the stock harness after cleaning and connection replacement from Vintage Connections. Drawings were made of each multi-pin connector, checked and rechecked.
One thing that is curious, I can disconnect both yellow leads from the tympanium that connect to the Y/G and R/G wires in the harness and only leave the red and black (positive and negative) wires connected and I get the same result.

Thank you again for your help, Geoff

It looks like you have the black battery negative wire connected to the B/W wire, which then is connected to the Tympanium brown wire.This is correct, but one of those wires also needs to connect to ground.

If you look at my diagram, you see the regulator/rectifier B wire splitting into two wires, which then connect to both the battery & ground.
If you look at the pic of my bike, you don't see the one wire splitting into two because its covered with electrical tape (look at top of pic to the right of the seat mounting bracket)

If I am right, with the Tympanium yellow wires disconnected & the key switched to off, add the ground.
If you get a spark there is something wrong & do not proceed further.
Otherwise, do your voltage check. It should be less that 12.8V because everything is running off of the battery.
Then connect the Tympanium yellow wires & repeat the test.
You should get 14.2 to 14.5V.

It is difficult to see from the picture but there is a 14ga. ground from the negative battery terminal to the frame.
There is no spark with the key off whether the yellow typanium wires are connected or not. I either configuration with the engine running there is a charging voltage of 20+ vdc.

Perhaps the GT250B's electrical system or generator is different from that of my T250, and the Tympanium is not capable of reining in the extra output.

Looking at the wiring diagram for the GT250B I see a voltage regulator coming off of the rectifier that then goes to ground.
Maybe that is something to try.

Thanks, Geoff

I'm no electrical wizard and I don't claim to be. But it seems if you never find the problem, you should be able to 'cure' the issue with a simple inline resistor.

The Tympanium has enough capacity for a T500, which has a bigger alternator than any of the T250 / T350 / GT250.

Where are you measuring the DC 20v?

At the positive battery terminal and a frame ground.

Using that ground as a reference, check for voltage drops of pretty much everything.
I expect that eventually you will find something that doesn't make sense given your 20V reading, or something that shouldn't be.
With a bit of luck that will point to your problem.

I don't know what all you did for the restoration -- the problem might be something simple like having a bad ground because you power coated the frame.