2 cylinders fail from time to time

[ventYl]

Try to get above mentioned varistor (based on datasheet any part compatible with 7K270 should be OK). If there is no additional damage to some other part it might be working again (if it is somewhat working it is chance that rest of CDI is OK). But the question is what caused such a damage to PCB?

[t6nis]

The guy whom i got it from said that he was tightening the positive plug on the battery and accidentaly shorted it, after that the bike stopped and never ran again. When i pried it open, the varistor was complitly burned. Both D1 diode and this varistor burned.

[ventYl]

So go for the replacement. I think that with transistors and caps you can get to price not more than 20 Euros on parts. IFF CDI is giving you weak spark then varistor is probably not in some very important circuit (thermal compensation?) and there will be need to replace other pars (elyts) too to get it working nicely. Good news should be that while CDI gives you some signal none of really expensive / hard to order parts should be damaged (mainly CPU, xtal, memories).

[t6nis]

Just to be clear, the CDI i have on my running bike is from Greg. It works, but yeah, has all sorts of problems that i have listed here. The CDI that is shown on the picture is from ebay, i got it with one of the side covers for free, i thought that i should give it a try first, before i tear open the working one and start replacing parts.

[ventYl]

oh well.... now I get it. try to replace the varistor and elyts, they should be cheapo. Then try if it gives you at least some spark. If not and/or will burn again you know it is dead :)

[t6nis]

okay, a little update. Changed the caps, did not do a thing, maybe a little change, but hardly noticeable on idle. Had some trouble @ startup once, lost spark, disconnected the signal plug, and it fired back up.
All points to what Greg said about the transistors, it seems like a grounding issue. I had to order the TIP150 and hope it arrives in time so that i can change those as well, at least i know what to do when the bike does not want to start.


FIY, i have opened up about 4 different CDI-s as long as i have had my bandit and every single one looks completely different
Heres the picture of the one i opened.

[greg737]

Just a thought that occurred to me... Have you inspected the bike's main ground lately?  The large Black wire that is bolted to the engine crankcase.  Sometimes a main ground can get loose or corroded.  Just a good idea to make sure all is okay at that end of the business

[t6nis]

This is getting irritating....
The no 3. cylinder keeps fouling spark plugs. This is the third spark plug in about 3-4 days...
All the other seem to work. The other thing i noticed is that when i accelerate it does not lag or sputter at any rpm, but when i keep it steady around 4-7 it starts to sputter, like one of the cylinders would be misfiring or runs lean.

[Squishy]

This is getting irritating....
The no 3. cylinder keeps fouling spark plugs. This is the third spark plug in about 3-4 days...
All the other seem to work. The other thing i noticed is that when i accelerate it does not lag or sputter at any rpm, but when i keep it steady around 4-7 it starts to sputter, like one of the cylinders would be misfiring or runs lean.

Btw, what makes you think this is an electrical problem?
The fiddling with the wires might just be a coincidence.

I've had quite some problems with running on 3 cylinders over the last 5 years, and they were always related to only two things:

- Runs on 3 only cylinders at idle --> pilot jets clogged
- Runs on 3 cylinders but comes alive (not always) at full throttle --> sparkplugs and/or the wires/caps have become wet/dirty. Might be caused by clogged spark plug drains and/or worn rubbers. It's possible that running on 3 cylinders fouls the plugs making it worse.

I was always able to fix the problem by cleaning the plugs with a steel brush and cleaning the spark plug hole.

Another possible cause might be one of your carbs having a problem with the needle causing too much fuel at constant throttle.

[Squishy]

Just a thought that occurred to me... Have you inspected the bike's main ground lately?  The large Black wire that is bolted to the engine crankcase.  Sometimes a main ground can get loose or corroded.  Just a good idea to make sure all is okay at that end of the business

Sorry for this hijack question.
Is this the black wire that you are talking about?
The starter motor is also grounded to it. It's basically under the cam chain tensioner.

https://dl.dropboxusercontent.com/u/22072961/MF/2015-06-24%2016.17.56.jpg
I'm having some ground problems myself, losing almost 1V somewhere on the ground.

[greg737]

Yes, that's the B4's main ground, on the aft starter mounting point.

I've seen main ground problems on other motorcycles, mainly Kawasaki.  The main ground on my 2005 EX250 was badly corroded when I bought it (the bike was only 4 years old at the time!).  There was corrosion (white-ish, fuzzy-looking stuff) down inside the aluminum threads cut into the engine block.  Cleaned it out, put some dielectric grease along the threads and things have been good ever since (9 years of ownership).

Also, it's important to trace back along that main ground to its connection at the battery.

[Squishy]

Yes, that's the B4's main ground, on the aft starter mounting point.

I've seen main ground problems on other motorcycles, mainly Kawasaki.  The main ground on my 2005 EX250 was badly corroded when I bought it (the bike was only 4 years old at the time!).  There was corrosion (white-ish, fuzzy-looking stuff) down inside the aluminum threads cut into the engine block.  Cleaned it out, put some dielectric grease along the threads and things have been good ever since (9 years of ownership).

Also, it's important to trace back along that main ground to its connection at the battery.

Where else is the wiring harnass grounded to the frame?
I've disconnected that main ground wire from the picture (indeed goes from battery ground terminal to crankcase) but I'm still measuring continuity from the frame to ground wires from the wiring harnass. Battery is removed as well.

[greg737]

Where else is the wiring harnass grounded to the frame?
I've disconnected that main ground wire from the picture (indeed goes from battery ground terminal to crankcase) but I'm still measuring continuity from the frame to ground wires from the wiring harnass. Battery is removed as well.

First: From the Suzuki factory there's nothing, I mean absolutely nothing grounded directly into the Bandit 400's frame.

There are a total of 4 (four) grounds on the B4's and all of them are engine crankcase grounds:  1. the main ground line from the battery, 2. the ground for the starter motor, 3. the Oil Temperature sensor is an old-school, one-wire "through body" thermistor-type of sensor, so as it heats up it grounds into the metal of the engine, 4. the Neutral Light sensor is also a "through body" sensor, it grounds into the engine when the "neutral bump" on the transmission shift-drum depresses its button.

That's it, a total of 4 grounds.  You can look at the electrical wiring drawing in the Bandit 400 and see there are only 4.

For the purpose of your measurements, though, if there's anything grounded into the engine crankcase it might as well be grounded to the frame because there's a very good pathway through the engine mounts into the frame.

[t6nis]

So, i found the problem. You can watch it in this video

https://www.youtube.com/watch?v=Uao_G5f-_Ns&feature=youtu.be

i have to change the spark plugs aswell, but at least i got all the cylinders firing correctly.

[ventYl]

Reply for your question asked in video is: yes the plastic part does come out as well. The are held mostly by dirt and emulsion tube tension. Underneath, there "secret O-ring lives".

The best way to get it out is to push the finger from inlet. After some time it will go out (and your finger will hurt a bit).