Help needed for my YZ490

[northernYZ]

Help needed. And no, I don't want directions to the nearest cliff to push the YZ490 off of.

When it runs, it runs great. But the problem is starting it. Usually, it eventually starts. Sometimes when my foot gets sore from kicking it, I leave it and come back to try again another day.

The spark seems weak, although it does have a spark. I can hold the end of spark plug wire in my hand and just receive a mild shock. Shouldn't this give me a strong jolt?

So how do I know where the problem is? The Ignition Coil, the CDI unit, or the CDI Magneto?

Can anyone tell me (or direct me to information) about how to test the Coil, CDI unit, and Magneto?

Thanks for your help!!

 

[91yz125]

wen holding the plug wire you should get enof of a golt to make you drop it. Have you checked the wire for cracks or is you coil not sealed properly? wen its hard to start is there allot of moister in the air? i have come acros this problem. were mi plug wire enters the coil there was a crack. you can use a voltage tester to find out what your bike is pussing.
good luck

 

[2strokerfun]

And no, I don't want directions to the nearest cliff to push the YZ490 off of.

That isn't the only solution. I think Rick Sieman has also suggested removing cylinder and using for flowerpot and about a dozen other suggestions!!!

Seriously, see if you can find someone with a good running 490 or 465 and borrow their ignition for about 30 minutes and see if it makes any difference.

 

[northernYZ]

Good ideas. But I don't know anyone with a similar bike to borrow ignition parts from. The spark plug wire also looks good, with no visible cracks. It has a weak spark whether it is hot or cold or dry or humid outside.

I hate to start replacing parts in a hit and miss fashion; been there done that too often. But would it make sense to begin with replacing the Stator coils? Am I correct that this bike has two of those tucked away behind the flywheel? If so, I guess I also need a flywheel puller - or is there another way?

 

[2 strokes for life]

northernYZ, well besides the throw it into a fire i dont know, is what i would have said if i had never ridden one but i have ad now i am bound to this. You are right about the 2 coils behind the flywheel but you will need the proper puller. I would think that the coil is failled and thats why you have a weak spark. bikeboneyard.com should have the parts you need at a good price. Have fun with it.

 

[northernYZ]

So, which coil is most likely to have failed? One of the two stator coils behind the flywheel or the ignition coil? From looking at other posts on this site, I'm inclined to think it might be the stator coils. But I don't know much about this.

 

[2strks4evr]

just out of curiosity,have you checked the compression?or how long has it been since it has had a new piston?when a big bore like that loses comp.it is hard to tell when you are the one kicking it all the time................does that sound right? :think:

 

[northernYZ]

No, I haven't checked the compression. But the spark is weak; as I mentioned earlier, it doesn't give much of a jolt when I'm touching the plug. Quite sure that it needs a stronger spark.

 

[76GMC1500]

I've seen a spark checking tool at some point in my life. It connected to the spark plug wire and had a ground clamp. There was an adjustable gap. I don't have my Yamaha TT225 manual in front of me, but I believe it said something along the lines of the spark should cross a 6mm+ gap.

 

[fatboyslim]

Just take it to a shop and get it the CDI tested then the coil then the stator if all that is needed, usually things like this come from the CDI box.

 

[2 strokes for life]

fatboyslim, its off topic but do you ride in the PNWMA for hare scrrambles? Or do you ride MX?

 

[91yz125]

i have seen a spark tester like mentioned in the other post. I use to work at a local yamaha dealer for about 10 months and all they do to check it is to see if the rite amount of current is going threw the wires, something simple you and a friend could do in your back yard. And ordering these parts could get expensive and you cant return electronic parts, well in canada you cant.

 

[bclark001]

ok the spark tester you can pick up at a local auto parts dealer what it does is it has a resister in it that acts as compression so if the tester has a good blue spark than it will spark the same under compression. the thing is that just holding the plug to ground does not take the same amout of energy to spark as if it were under compression. and if i had to guess the weak spark you are describing prolly would not spark under compression or with the spark tester

let us know how its going :bang: I hate when things break

 

[Someone]

Try tipping the bike over when the gas is turned on. Wait till you get some gas spilling out of the overflow. Ever since my 01 YZ 250 (I now have an 05) I do this when the bike is cold. Starts first kick every time.

 

[helio lucas]

northernYZ
i think the best you can do is getting a service manual and chek the coils using a multimeter in ohm´s scale...
i don´t know if the manual of that bike have the readings listed but nowadays most (if all) have...
is quite easy and everything you must know come in the manual... its not expensive and for a next time you have a malfunction you already have it...

good luck...

 

[northernYZ]

Thanks for the ideas.

Did you ever buy something and forget that you had it? Last night I found a Clymer's repair manual for the YZ on my bookshelf. Duh!! :bang: I guess I bought it a few years ago when I changed the fork seals.

Anyway, I ordered a flywheel puller and the two stator/source coils today. A few people told me they are the most common parts to go on these ignition systems. They are relatively cheap at $39 for the pair. So I'll try those and hope for the best.

 

[2strokerfun]

I've seen a few weak ignition coils, but my experience with stator coils is that they are either sound or don't work at all. Hope I'm wrong and you solve your problem.

 

[northernYZ]

An update for those interested:

The Stator coil and flywheel puller arrived today. I installed it and a new spark plug and checked for spark; it now has a blue spark at the plug. The bike started on the fourth kick. I shut it off a few times and tried to restart it. It started second or third kick each time. So far so good!!

 

[kelsorat]

Do a search or ask on this site for Bundy's email. He is an expert on YZ490's.

 

[2 strokes for life]

Sweet. Sounds like a good thing is happening for you. My project is still on its way.