What's new

Spark Plug Coil Resistance On A 2005 CRF250X?

DJ_MI

Voted Class Clown 1937
Joined
Feb 7, 2022
Member Number
63
Posts
1,838
Location
SE MI
I bought a CRF250X last week. I took it out on Sunday and it ran great. After it cooled down it's almost impossible to start. I posted the story here: crf250x-mega-thread.

In the course of troubleshooting I checked the resistance on the ignition coil. The coil pack secondary resistance is good @ 5.67 kOhms. However, the resistance across the connector terminals is 0.7 ohms. The spec range is 0.07-0.10 ohms which puts mine at 7x what the upper limit should be.

How critical is this measurement? Obviously it's out of spec and I'm going to replace it, but does anyone have any first hand experience with how much that impedance affects function? Could this be the cause of my hard starting issue?

Thanks!

2022-07-14 19.43.00.jpg
2022-07-14 19.45.12.jpg
 
If you are getting a reading like that on a coil, its burnt.

Basically to a multimeter the only resistance on a DC coil (in theory) is the length of wire. The reason that it increases is called skin effect (if you want to google that up) but if you are x7 the spec resistance, its done, and depending on the power source for the coil, its likely not providing a very large spark anymore.
 
The problem was the intake valve clearance. I shimmed them to spec and it runs like a champ, even with the "burnt" coil.

I replaced the coil afterward anyhow and it didn't seem to make any appreciable difference. At least I have a spare coil now. Thanks though!
 
The problem was the intake valve clearance. I shimmed them to spec and it runs like a champ, even with the "burnt" coil.

I replaced the coil afterward anyhow and it didn't seem to make any appreciable difference. At least I have a spare coil now. Thanks though!

Yeah, so this is one I deal with at work a lot. Its good....till it isn't and its not going to give you any warning when it totally give up the ghost.

That sort of thing is the main driver of overtime over the last ten years or so.
 
I recently helped chase down a similar problem on a truck. The owner didn't want to buy an OEM ignition module and picked up the cheapest one he could find, which tested bad out of the box. Rather than address that because it was new and must really have been ok, he continued chasing phantom solutions, got frustrated, and limped the truck to a shop. It cost him $150 labor to determine that the new ignition module was junk, and $80 for a new OE part.

The good deal on a cheap set of plug wires worked out the same way. :fpalm

yes, much like fork seals, a lot of the time its better to use OEM, vice E-Bay/Amazon crap.

There are exceptions of course, but you don't get those aftermarket items cheap either.
 
yes, much like fork seals, a lot of the time its better to use OEM, vice E-Bay/Amazon crap.

There are exceptions of course, but you don't get those aftermarket items cheap either.
What a crazy coincidence that you bring up fork seals. Mine started leaking shortly after I fixed the valves.

I guess the world is just full of crazy coincidences, my neighbor has a 675 Daytona and his fork sprung a leak right about the same time. He was nice enough to offer to help me service mine but he drinks like a fish, smokes like a chimney and litters the butts everywhere.
 
What a crazy coincidence that you bring up fork seals. Mine started leaking shortly after I fixed the valves.

I guess the world is just full of crazy coincidences, my neighbor has a 675 Daytona and his fork sprung a leak right about the same time. He was nice enough to offer to help me service mine but he drinks like a fish, smokes like a chimney and litters the butts everywhere.

I would deal with the fallout.

I have said many times, bike shops exist to sell me bikes and do my fork seals. I HATE doing forks, I have been able to since I was like 9, but I hate it, they are a messy pain in the ass and I can pay to have someone else deal with it. I will do valves first.
 
Back
Top Bottom