Fixed CDI unit but still some problems

[SubieHo]

Ok, I've read all the CDI faqs on this forum and replaced the five capacitors on a spare one CDI box.

From PitterB4:

"Cap-se 1050 10UF/50V heat reated - 150Dc

Cap-se 47-35 47UF/35V heat reated - 85Dc

10uF25v (85deg c)"

I couldn't find a 10uF/50V heat rated up to 150 C, but found a couple heat rated to 105 C -- same as the orginal ones.  Was this a typo by PitterB4.

I also replaced the 10uF/25V (85 C) with a 10uF/25V heated rated up to 105 C, but I can't imagine that should make a difference -- it just operates across a broader heat range.

The bike now starts and will run fine, but there is sometimes a slight hesitation at idle and it will not restart when when the engine is hot.  It will fire up only after the bike has cooled a bit. 
However, if I push start it, it will then run fine.    I

'm sure it's the igniter box because the the bike shows none of these symptoms with the good box installed. 

Any thoughts?

[PitterB4]

I have no idea.  Sorry.  That was NOT my post.  As an admin here, I just copied and pasted a post from a previous iteration of this board into the FAQ.  CDI issues were, I think, the only problem I DIDN'T have with the old B4!  Good luck!

[Thief400]

First thing i would check is if there is spark whn the bike is hot and will not restart. Its possible that you have a coil or coils going bad as they heat up. They are under alot of heat load seeing as they are just above the engine and behind the rad.

[SubieHo]

Good point.  I've had ignition coils that would short out when hot before, but in this case, I'm sure it's the CDI unit  because when I swap in my good CDI box, it will fire right up and exhibit none of these symptoms. 

I'm going to try replacing the 10uF/25V/105C cap with a 10uF/25V/85C cap to see if it makes a difference.

[SubieHo]

Well, I swapped in the a 10uF/25V/85C capacitor, and it didn't make a difference.  So then I discovered that a couple of solder points were touching a couple of the surface mount resistors.  I cleaned those spots up , then reheated all the connections for the five capacitors.  The CDI box is now performing flawlessly. 

The engine feels more powerful, but perhaps that's because I cleaned up a carbs a bit.  I had to pop them off to replace the throttle cable.

[SubieHo]

Ok, just a little update.  I spoke with my uncle, who's an electrical engineer, this evening.

I asked him about voltage and temperature ratings, and he says that all circuit boards are essentially the same.  He says that on "high-tech" devices such as the CDI unit, one can substitute higher voltage and higher temperature ratings for lower ones.  With the exception of circuit boards on which the capacitor doubles as a voltage regulator, which is a cheap and unreliable way of designing a circuit, he says that that if you can get the higher rated capacitors to fit, they will hold up longer.  A higher temperature rating just means that the dielectric inside the capacitor is better.  Capacitors are relatively inexpensive, but I guess it affects the bottom line when you're mass producing them, hence Suzuki uses these lower rated caps.

In lieu of the stock ratings, I'll wind up using these other ones I found:

Stock:                   Replacement
10UF/50V/105C       same 

47uF/35V/85C         47uF/35V/105C

10uF/25V/85C        10uF/25V/105C 

You can also use the 10uF50V capacitor in place of the 10uF25V capacitor. 

Also, he would have suspected the transistors (on the two heat sinks) burned out before the caps so apparently, the latter is a relatively uncommon occurrence.