No spark, what could it be?

[Morvo]

I'm going to break down my situation with my 1995 KX250 so you can get an idea of what is going on.

When riding our bike the revs would not top out, instead it would get up to just before the powerband, or thereabouts, and it would rev like a limiter was in affect. I put it down to something to do with the stator again or the CDI unit, so I ordered a second hand working CDI, and also bought a set of stator coils and installed them on the original stator plate, along with a new pickup coil. I checked for a spark after putting all of this on but I got sod all, changed the plug for a new one, still the same results. The kill switch has been disconnected and the wire is fully insulated, so that rules that one out. I checked all of the resistances on the multi plug from the stator and it all checked out ok. Do you think it could be the HT coil? I can't see why the bike would go from running (not well, granted, but it still ran) to a complete dead dodo! Could the running problems of the bike be a sign of the HT coil breaking down? Is it possible for the flywheel to lose it's magnetizing strength, even though it still seems to attract to the stator coils quite well!

 

[Morvo]

Ok, I bought a brand new OEM HT coil and our bike still has no spark. I put a voltmeter on the terminals from each coil and got a mate to kick the engine over, a small amount of voltage is present (max of 2v on one coil and the other was even more feeble). I also put the voltmeter on the spark plug cap and the other wire to ground, again I got the slightest amount of current 0.18v perhaps, hardly a powerful voltage to cause a spark across the gap of a plug! The problem definately lies in the stator area, but seeing that the coils are brand new what else could it be other than the flywheel??? I know it is extremely rare for a flywheel to lose it's magentizing strength but I seriously think that is the problem here. The flywheel has been off the bike since like October last year on the floor of my mates shed so it hasn't been proporly stored. As I mentioned before, it still has magnetisim but I'm sure it doesn't seem as strong as before, it used to pull over the coils quite violently before, now it seems like nothing, even though there is :) Maybe I'm a rare case or maybe my coils are just gay? What's the peeps view on my bikes problem?

Ta!

 

[RM_guy]

That sounds like what I just went through. No spark...put in new stator...still no spark. It turned out to be a broken wire between the stator and the CDI box. Check for continuity between all of the wires. Mine was an intermittent break so wiggle the harness when checking.

 

[Morvo]

That sounds like what I just went through. No spark...put in new stator...still no spark. It turned out to be a broken wire between the stator and the CDI box. Check for continuity between all of the wires. Mine was an intermittent break so wiggle the harness when checking.

Continuity through the wires is fine, the resistance of the coils checks out fine, the only other problem I could think of that might cause no spark, or even a weak spark, is the position of the pickup sensor. When the flywheel goes over the crankshaft and it is torqued up the magnet on the flywheel does not line up face to face fully with the pickup sensor, it sits about half over it. Would this cause problems?

 

[RM_guy]

If not enough of the magnet passes by the pick up coil it may not generate enough voltage but it doesn't need a lot anyway. Does it look like it moved?

If everything else checks out OK then the CDI is probbely bad.

 

[Morvo]

If not enough of the magnet passes by the pick up coil it may not generate enough voltage but it doesn't need a lot anyway. Does it look like it moved?

If everything else checks out OK then the CDI is probbely bad.

The pickup does look like it has moved over time, I' m wondering whether the flywheel has worn away slightly from me constantly taking it off and on so it now slips further down the shaft putting the sensor out of position.

The CDI was replaced recently, I think I can safely rule that one out seeing as though the problem still persisted before I changed it over.

 

[Morvo]

Well, I changed the pickup once again for a different one as the resistance of my Ricky Stator one seemed a tad too high. I then adjusted it to be more inline with the flywheel pickup, having to shave some metal from where it sits on the stator plate to sit lower. I thought the CDI to stator coils multi-connector plug seemed a little weak for it's age, so I snipped it off and replaced with bullet type connectors and taped it all up. Took the plug out, got a mate to kick the bike over and alas, we have a spark! :cool: After a few kicks with really really old fuel in she fired right up, albeit a little smokey but that soon cleared once she had heated up :) She tops out fine now unlike in my previous scenario http://www.dirtrider.net/forums3/showthread.php?t=138920 just can't wait to hit the track and give it some! I reckon you could have been right Rm_Guy with the wires needing a wiggle, I should have done each thing I tried one by one instead of all at the same time, nevermind hey! :p

Cheers!

 

[RM_guy]

Congrats! :)