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Thank you so much for the info, its greatly appreciated!   

Hi all, i have a 1978 YZ250 in need of new clutch plates (steel and fiber) which seem hard to find, they are the same diameter as my 1977 RD400, would the RD plates work well in the YZ? Or could you recommend a different alternative? Thanks in advance.

Ok, thanks again for all the info guys, in just about ready to put power to it after installing a new harness and regulator/rectifier. There is a lot going on in that headlight bucket but I think everything is right. 

I was using 5 mah battery, is that too much, or should I get a 4.5 mah?

thats what you need.

you can, i did when i first got it way back, but also had a capacitor (which is now IN the regulator). However, since i run a zeeltronic controller now, i started running a battery as it needs power to fire up. Some say it doesnt, but i dont want to kick it over forever to start.  If you arent running one of those, no battery is needed. 

I run a zeeltronic controller as well, and what a difference that makes! I will buy a new battery too. Thanks again for all the help!

yup, same battery. cant answer on the switch.

https://www.economycycle.com/shop/yamaha-rd250350400r5ds6ds7-parts/electrical-ignitions-lighting/ignition/mzb-regulator-with-built-in-capacitor/

This is the part i need, correct? It looks identical to what i have, and it says with that you can run the bike without a battery, have you ever went this route Mark?

I believe the battery i have now is very similar to that one, i had bought it at Radio Shack. Kind of a bummer those closed up.

My key switch is original on the bike, should i replace that as well? Did anyone re pop them?

I have an alarm battery in it now, it's been good but not a bad idea to replace it.

Thank you for all your help everyone, I really appreciate it!

yeah, you need to unplug the blue wire from the coil to the relay if its there.

yup. my battery was 8 yrs old. then pow.


and yes, the new regulator works with the older units.

I did that, it has spark, im Happy about that! What is a good battery to get, and is economy cycle open?

I hooked everything back up except the red wire for the regulator, no spark.   

as long as it doesn't rely on a relay to kill the bike. you may have to bypass that if its there, but then you have to kill it another way. 

id bet the regulator fried due to over charging like mine did. how old is the battery? mine dead shorted as well.

The battery im pretty sure is around 10 years old, maybe i should replace that as well. I had not ran the bike in probably a month due to winter setting in up here in MN, went to start it and there was no power to the key, fuse was popped, so it went bad while sitting.

The red wire from the regulator goes through the fuse to the battery, like it should. First thing i tried was unplugging the key switch with no luck. Then i tried unplugging the black wires going to the stator, still blew the fuse, if i unplug the red wire to the regulator, it does not blow the fuse. So that tells me the main harness is fine. What do you guys think? Oh and all this is happening with the key off, i was going to fire up the bike one day and noticed out of the blue i had no power when turning the key on, and noticed that fuse was blown.

The regulator/rectifier is blown. It is shorted. You proved it with those tests. Unplug it and install a new fuse and the bike should start. That will prove everything is ok with the cdi.

So the bike should start with the regulator/rectifier disconnected?

The red wire from the regulator goes through the fuse to the battery, like it should. First thing i tried was unplugging the key switch with no luck. Then i tried unplugging the black wires going to the stator, still blew the fuse, if i unplug the red wire to the regulator, it does not blow the fuse. So that tells me the main harness is fine. What do you guys think? Oh and all this is happening with the key off, i was going to fire up the bike one day and noticed out of the blue i had no power when turning the key on, and noticed that fuse was blown.

That tells me the harness isn't fine and the red wire is finding ground somewhere. Most likely a portion of uncovered wire rubbed through the shielding and is grounding out.

When i unplugged the red wire going to the regulator/rectifier, then the fuse did not blow.

The red wire from the regulator goes through the fuse to the battery, like it should. First thing i tried was unplugging the key switch with no luck. Then i tried unplugging the black wires going to the stator, still blew the fuse, if i unplug the red wire to the regulator, it does not blow the fuse. So that tells me the main harness is fine. What do you guys think? Oh and all this is happening with the key off, i was going to fire up the bike one day and noticed out of the blue i had no power when turning the key on, and noticed that fuse was blown.

Hi! On my 77 RD400 i have a powerdynamo ignition installed, it has worked great for close to probably 8 years now roughly, have any of you with this ignition setup have an issue with the regulator/rectifier causing a short and blowing out the 20 amp main fuse? And is there a way to test it with a meter to determine its bad? Thanks in advance.