Jump to content

1981 XT 250 overcharging


Recommended Posts



I have a 1981 yamaha xt 250 with electrical problems.

Its a 6V system with seperate voltage regulator and rectifier as far as i understand. I have changed the regulator and cdi box with second hand parts but problem still persists.

At the moment we are still getting 40V AC at the battery. Does someone know what i can look at or change?

Link to comment
Share on other sites

Do you want an ad-free experience? Join today and help support the Yamaha Owners Club.

Yeah... 40V doesn't sound right at all!

I have no idea how to fix the problem or even what the problem is, but you could always try to suck up some of that power by slapping a load of xenon headlamps on the front like a 1970s Mod Lambretta..! 🛵:eusa_dance:

Other than that, I'm sure someone else will have a better idea! :D

Link to comment
Share on other sites

Hi there,

The purpose of the regulator is to 'regulate' or reduce the voltage!

The generator produces the AC voltage, and if you were to measure directly off the coils, on the charging circuit (with nothing else connected) you will indeed find a rising AC voltage depending on the revs... the faster the revs the higher the output. On a DT 175 MX you will see 26v at 6000revs.

The REGULATOR 'clips' this voltage back down to 6 volt (on a 6v bike and down to 12v on a 12v bike) and it is this reduced voltage which charges the battery. Otherwise the battery will get fried on the unregulated  output of the generator.

So if you're getting 40v it strongly suggests the regulator is not doing its job.


You might want to have a read of one of my popular posts on a conversion of my DT175 from 6 v to 12v. It's a long read but I do detail how all the parts work, which might help you understand it. I do note also that some XT owners have indeed used my post to convert theirs. However, i must point out my usual disclaimer: this is what I did with my DT175MX not any other bike.

Moreover, I'd also like to add that 10 years later...my 12v conversion is still working perfectly fine.

hope this helps.



  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Who's Online (See full list)

    • There are no registered users currently online
  • Recently Browsing

    • No registered users viewing this page.
  • Create New...