1977 xs650 w/ PMA & Sparx Capacitor issues

So I've never worked with this kind of bike and have been helping a "Friend".

The Issue:

Bike ran great, fired right up, seems to be timed right with the PMA, go for about a 10 mile ride, bike dies. Nothing. Pull the sparx capacitor, hook up a battery, bike fires right up.

We take the issue as a problem with possible location, and vibration killing the capacitor.

Order a new Capacitor, relocate it, and now the bike will not fir with the capacitor. still fires right up and the timing sounds great with a battery attached.

Redid the ENTIRE wiring to make sure theres no shorts and that everything is getting the juice it needs. Still no luck.

So now the wiring is all tight, and the bike will fire with a battery in place of the sparx capacitor. But still nothing from the SECOND, Brand new Capacitor.

Maybe we should upgrade capacitors? Not sure.....Any advice is much appreciated. I apologize if theres already a million threads on this, I just never read the Japanese forum.

run a battery. Problem solved

A permanent magnet stator will run without a battery. But it runs infinitely better with one, smoother firing from the coil, no flickering from the lights both front and rear, and your bikes electrical won't leave you stranded.

I'm not sure which way that you have that thing wired and if you are dead set on running without a battery I suggest doing a shit ton more research on how permanent magnet stators work in relation to building currents (charge) and how that relates to your system and how you have wired it.

Speaking from running a bike both ways (battery and capacitors) the battery always made the bike run smoother with better response on the throttle and infinitely better lighting at night.

With the capacitor you may want to try and run your lights and firing systems on 2 separate circuits. That way at least you are taking some of the load off until you switch your lights (brake and head) on. It will help but not solve your current issue. Also I'd go and find a 12v 1amp (min) small gel sealed battery to help getting the bike started at the very least

yea theyre dead set on not running a battery.....its just so frustrating since the bike ran great for a week or so of testing and what not, then when riding on its maiden voyage 10 miles in the capacitor is shot

how do you know its the capacitor? do you have new coils? you could have fucked up your regulator. i dont know, i havent gotten to the pma on my shit yet so these are just basic shits.

with the battery your getting a good solid spark?

yea it runs like a fricken top with the battery


The regulator is brand new and came with the PMA. Would it run ok with a battery hooked up if the regulator was gone?

Im guessing then since the regulator could be bad it wont send juice to the sparx and make it start?

Sorry im kind of in the dark here, just trying to diagnose whats going on with it. Im used to running a magneto on my personal bike, which seems a hell of a lot easier than this!

Check the voltage coming from the regulator. Should be >12 and <15.5vDC. If you have no power coming from the regulator, then the cap won't help you. The battery is powering the bike without the charging system and when the battery goes below 6vDC the bike won't run anymore.

I was thinking it could be the regulator as well, somehow the power isnt being transferred from the PMA to the Capacitor....hrmm

did you get it from hugh? hell know whats up

Who supplied the PMA? I plan on running without a battery.

We need to know the voltage at the Capacitor. Without that, we have no idea whats going on. Putting in a battery may just be a bandaid for bad wiring, or a PMA that isn't putting out enough power or improperly wired. The battery may last longer, making you think the Capacitor was the problem, but eventually the battery will die also...

Get us voltage AT the capacitor at idle, and at about 2K RPM...

IF the Regulator is bad on a PMA, you will usually get too much voltage... If you are getting to low of voltage, you usually have a poor connection on one of the yellow wires from the stator-regulator connection, or the stator is dead...

Also, make sure the Regulator is getting plenty of air flow, not mounted in a box or something like that. That will kill one easily

Also, make sure you aren't running a super high draw Headlight or Taillight. These items usually need a battery to keep operating properly, whereas a low draw headlight/taillight can operate from a Capacitor without issue..

But without some Voltage numbers, all we are doing is guessing.

Thanks Punkskallar(sprackta snutskallar).

Seems like the culprit was a cracked regulator. They just ordered a new one. Thanks for all your help guys.