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Problems With Spark


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BLAH...... I'd like to start off by saying that. I have taken up the hobby of riding and so far has proved to be very enjoyable, expensive as hell but enjoyable. I bought a bike off of craigslist that seemed to be a great bike, me being so new to the sport i really didn't know what to look for thus leading me to find alot of little problems with the bike after the purchase that i should've been aware of when i bought it lol. O well its a great learning experience and felloow riders here on TT have been more then helpful with diagnosing problems and preventing other problems.

Here's the predicament that I'm in now..... While out riding i seem to lose power to my bike without any reason. i figures that i had fouled another plug because i had that issue the time i was out before, After changing my plug it didn't resolve my issue so we tried another, still no luck. A friend i was riding with with a little more knowledge than myself (not much but a little) suggested that it might be a fuel issue so as soon as i got home i tore my carb apart and cleaned it out. All a learning experience for me haha but it went smooth with a little help from youtube still not the results i was looking for. i could smell fuel on the plug so then realized it wasnt a fuel issue :eek: pulled the plug and tried grounding it to the engine to see if i had a spark YAY i dont have a spark well thats that. now what i wanna know is before i spend 150$ on a new spark plug coil is there anything i should check before i do so? how do i ensure that it is my spark plug coil and not something else.

Im posting this in advance this time because i replaced my clutch on my bike and then replaced clutch cable when apparenty all i needed was spacers on the exsiting clutch cable wasted 250$ when it wasnt needed not gonna waste more $ i dont have :banana:

thnx in advance guys

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Ok, first off your paying wayy to much for parts. :banana:

Second was the plug grounded good when you tested it? to bare metal?

I'm sure what your having is a cheap issue to fix, even if it is the coil, you can get one for $10

yes it was grounded good, yamaha quoted me 150 for coil advised me try to replace the boot first which is only 15$

the only reason my clutch cost me so much was because i ran into a buncha bolts and shit that were stripped and had to be replaced

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A volt meter is your friend!!!

You can check to see if you have a closed circuit with your spark plug boot easily with a volt meter, thus needing to know if you need to replace it or not.

Coils seem to last forever on these bikes, however there's probably the odd one that does go out, chances are though it's not yours :banana:

With a volt meter the resistance of the coil can be tested, letting you know if it is in spec.

If I were you I would invest in a Yamaha service manual, the one from the factory not a haynes or a chiltons etc.

Right now you should be pulling the harness and checking to make sure that all the connections are clean. Using a tooth pick or even one of those plastic tooth pics with the rubber cleaners on the end, you can clean out your connections. Pull the coil connecter and clean the contacts with the pick and carb cleaner.

Check the stator, this is where the current is produced to actually get a spark, chances are your gasket for the stator cover is gone and mud/dirt has leaked onto the stator itself. Pull the cover and check around the flywheel, it should be very clean, the best way to look at this area is to pull the flywheel with a flywheel puller and check the stator physically.

The service manual I believe tells you how to check your stator, but I can't recall what the procedure is.

Maybe some others here can give you some more tips.

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One thing to keep in mind when checking stators...

Obviously you will need to know the prescribed resistance for each winding. Bear in mind that at room temperature you may get perfect results.

When the stator warms up, faults can resurface. I have come across two stators that seemed fine. Placing them in an oven for a while and then checking revealed that they were in fact faulty.

An important component of checking electrical faults requires the jiggling of cables and connectors. Some times bad joints form not just at connectors but also within the loom. Test the resistance between the ends of cables (ignition related circuits) whilst flicking / vibrating the loom. I've solved many ignition faults doing this (not just on bikes).

It also wouldn't hurt you to completely isolate the kill switch. They have a habit of playing up. Remove it from the loom and open / close circuit the wiring manually while testing the operation of the engine. The switches can lead to high resistance joints on the ignition circuit. This often happens as the switch becomes damaged from water. Anyone whose owned a late model KTM will appreciate this tip :banana:

If anything, I'd start by focusing on the kill switch FIRST and then move to the stator and loom. Grab yourself an ohm meter. They're an exceptionally handy tool.

Berg

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WOW i pulled off my stator cover and realized that the bike wasn't as well maintained as i might have thought it was at the time of purchase. I have yet to fix my problem but when i saw a layer of dirt about 1cm thick in the bottom i concluded that thats the origin of my problems. i will keep thinkgs posted as they unravell. thnx alot guys really appreciate the advice

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im having a similira problem, although i figured i had a bad ground somewhere because it always seemed to happen when i went through water. i pulled my bike bike apart tested my coil and cdi box and stator and found no issues, i even bought another yz250 a few years older but same relative design to cross reference all 3 original parts. after doing so i came up with no answers and still no spark. if i were to put my stator in the oven like you sujested then what temperature should i set the oven to and how will i know its a failure.

please help me im dieing to ride !

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One thing to keep in mind when checking stators...

Obviously you will need to know the prescribed resistance for each winding. Bear in mind that at room temperature you may get perfect results.

When the stator warms up, faults can resurface. I have come across two stators that seemed fine. Placing them in an oven for a while and then checking revealed that they were in fact faulty.

An important component of checking electrical faults requires the jiggling of cables and connectors. Some times bad joints form not just at connectors but also within the loom. Test the resistance between the ends of cables (ignition related circuits) whilst flicking / vibrating the loom. I've solved many ignition faults doing this (not just on bikes).

It also wouldn't hurt you to completely isolate the kill switch. They have a habit of playing up. Remove it from the loom and open / close circuit the wiring manually while testing the operation of the engine. The switches can lead to high resistance joints on the ignition circuit. This often happens as the switch becomes damaged from water. Anyone whose owned a late model KTM will appreciate this tip :banana:

If anything, I'd start by focusing on the kill switch FIRST and then move to the stator and loom. Grab yourself an ohm meter. They're an exceptionally handy tool.

Berg

Awesome advice, this must be why the manual gives resistance values for coils/windings at particular temperatures! Didn't know that.

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  • 4 months later...
... im dieing to ride !

Me too, I have the same problem, I tested all resistances and they checked the CDI seems to be the only part seemingly uncheckable. I got no spark but the bike went home alright. When hot it won't start by kick only by push start. No indication it could be the CDI going out. No misfiring, just bad starting when hot. Cold it did well, 'till today that is.

It happened after riding though water. I cleanded everything pulled the stator, pulled the coil cleaned and unrusted all what was rusted. Still no spark.

Regards

Arnego2

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