93 RM250 No/Weak Spark

[WaldoVH]

I just replaced the coil, CDI, Pulse sensor and Magneto. The bike ran great for a couple of months then yesterday I was taking a rip ride up and down the alley before I loaded the thing and it died. It died in exactly the same way it did before I replaced all those parts a few months back and it was the coil. I can feel a weak shock when I hold the plug but no spark.

The service manual says the resistance between the plug cap and the primary wire should be between 11,000 and 16,000. Mine is 16,998. There seems to be pleanty of voltage from the Magneto to the CDI. I plugged in my old CDI and got the same weak spark.

Is it time to drop another $85 on a new coil or is 16998 close enough and I have some other problem?

 

[whenfoxforks-ruled]

Seems if it is in spec then its ok, did you check the key holding the rotor in place?

 

[WaldoVH]

Seems if it is in spec then its ok, did you check the key holding the rotor in place?

Yes, I did.

16,998 is just out of spec if my Radio Shack Digital Multimeter is calibrated correctly. I always figured that if a coil died the reading would either be a short or open not just a little high.

 

[BSWIFT]

Yes, I did.

16,998 is just out of spec if my Radio Shack Digital Multimeter is calibrated correctly. I always figured that if a coil died the reading would either be a short or open not just a little high.

Basically you are correct. Typically a coil will go open but either way you are out of spec. Did you put in an OEM coil? I would inspect the flywheel side of your case carefully and check for moisture. Check all of the wiring carefully for scuffs or scraps and insure that you do not have an unwanted ground. Heat is the next biggest enemy of electronics so do some thinking on where the problem is originating from.

 

[WaldoVH]

It is an OEM Coil. There didn't seem to be any moisture under the flywheel cover. I pulled the flywheel off and took off the ignition plate to make sure none of the wires from the magneto had broken or shorted out and they look good.

I checked for continuity on the pulse sensor wires. I hooked up my analog multi meter and shook the wires hoping to find loose intermittend problems but there were none.

 

[whenfoxforks-ruled]

I'd be having fits,replaced all that and it happens again! Something is screwing up your electrical system, bad ground,maybe somebody is hitting your bike with an emp, kill switch grounding out,I really hate asking, but what kinda plug?

 

[WaldoVH]

NGK Plug. The kill switch is fine, I checked it and unhooked it. I welded my kickstand plate to the frame with my MIG do you think that may have boogered up something?

I am having fits, halve the time I've owned this bike it's been broken.

 

[whenfoxforks-ruled]

Oooooooooooohhhh Noooooooooo!!!!!! Its been a long time since messing with welding on dirt bike frames, but I'm pretty sure that the cdi has to be removed in order to weld.

 

[WaldoVH]

I have a spare working CDI box that was not on the bike when I welded it. I swapped it in to see if I got any spark, no dice!

I thought mabey it wasn't a good idea to weld on a bike but it was such a little weld and taking the CDI off is such a PITA......I won't do it again.

I'll be ordering up a new coil tomorrow.

 

[02yz426f]

The coil is bad. They usually fail when hot and test to be good when they get cold again. Get a hairdryer and heat it for 15 minutes then test the resistance. If the coil is still good, it might be the plug wire.

 

[WaldoVH]

The coil is bad. They usually fail when hot and test to be good when they get cold again. Get a hairdryer and heat it for 15 minutes then test the resistance. If the coil is still good, it might be the plug wire.

I hooked the coil up to my multimeter and fired up my heat gun. The coil started out reading 16,998 and as it got warmer the resistance started creeping up. By the time it hit 18,000 I had added 02yz246f to my short list of really friggen smart people!

Thanks! :)

Do you think me welding on the frame is what screwed it up? The bad coil does have less than 4 hours on it.

 

[02yz426f]

I have heard welding on the frame fries the coil, but I do not know from experience. Try a new coil and let us know.

 

[WaldoVH]

I got the brand new coil and installed it and still no spark.

I did get it running but I'm really not sure why it stopped running.

I think I had a bad plug boot but it took a fresh plug to get a fat spark.

I have some more welding to do but I sure as heck will take off the coil and CDI this time! :)