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-   -   YZ250-lost spark, all tests checked out OK... (http://www.dirtbikeworld.net/forum/showthread.php?t=116942)

LABRADOR Coaster 01-01-2015 12:13 AM

YZ250-lost spark, all tests checked out OK...
 
Good morning gentlemen,

A couple weeks ago I tipped over on my bike a couple times, couldn't,t get her to go, new plug no spark.
since then I have run thru all the diagnostic test shown in the shop manual.

Stop button checks out
Primary coil resistance was 00.3 ohms (acceptable range 0.20-0.30)
Secondary coil. Was 12k ohms (range 9.5-14)
Spark plug cap. was 4.6k ohms (4-6)

Pickup coil resistance was 280ohms (248-370)
Source coil #1 was. 806 ohms (720-1080)
Source coil #2 was. 50 (44-66)

The manual says to replace the CDI unit if all these test are good and run tests again, wondering if there is a way to test the CDI unit.
The bike is a 2007 with low (50) hours. In my shop with low light I can see spark on the plug if I kick real hard. Tried priming her to see if she would fire but nada..all the wiring harness seemed to be in good shape also.
Also...I ordered a secondhand Cdi box from Ebay, coulda swore I saw YZ250 in the list of bikes it fit, next day I noticed that the CDI is for YZF 250 which is a 4 stroke. It looks exactly the same so hoping it will work, what an idiot!!...

Any advice would be appreciated, thanks.

Wilson

Kero 01-01-2015 11:53 AM

Disconnect the kill switch.
A useful bit of advice given to me recently, the switch measured ok but was only allowing a weak spark through.

Pale Rider 01-01-2015 06:32 PM

Quote:

Originally Posted by LABRADOR Coaster (Post 1895120)
Good morning gentlemen,

A couple weeks ago I tipped over on my bike a couple times, couldn't,t get her to go, new plug no spark.
since then I have run thru all the diagnostic test shown in the shop manual.

Stop button checks out
Primary coil resistance was 00.3 ohms (acceptable range 0.20-0.30)
Secondary coil. Was 12k ohms (range 9.5-14)
Spark plug cap. was 4.6k ohms (4-6)

Pickup coil resistance was 280ohms (248-370)
Source coil #1 was. 806 ohms (720-1080)
Source coil #2 was. 50 (44-66)

The manual says to replace the CDI unit if all these test are good and run tests again, wondering if there is a way to test the CDI unit.
The bike is a 2007 with low (50) hours. In my shop with low light I can see spark on the plug if I kick real hard. Tried priming her to see if she would fire but nada..all the wiring harness seemed to be in good shape also.
Also...I ordered a secondhand Cdi box from Ebay, coulda swore I saw YZ250 in the list of bikes it fit, next day I noticed that the CDI is for YZF 250 which is a 4 stroke. It looks exactly the same so hoping it will work, what an idiot!!...

Any advice would be appreciated, thanks.

Wilson

Welcome to DBW, id start with the easy to eliminate things first as Kero has mentioned, including a new plug. After all tests show in specs it will then only leave the unkown quantity being the CDI. I would also disconnect every wire harnes plug clean and reconnect including all earths. I would check the harness for hidden or internal breakages or pinches too.

A word of caution with the YZF CDI, I would check the part number which can easily be done on any online OEM part supplier, you could do damage to other electrical components if it creates more output that can be used. If you havent received it and they havent sent it just contact em and ask em to cancell and apologise. If not I would check the specs before you use it. ^dunno
Good luck with it it can be frustrating but stick with it..:cheers

gasser nate 01-01-2015 08:52 PM

Hi mate, as said check all earths for continuity back to the CDI plug, for that matter go through the whole harness with a ohm meter to make sure there are no breaks/shorts in it either. Also check for spark with out the plug cap installed, I have seen a few of them measure out ok but give weak spark.
Pretty sure the Yzf CDI will not fit..

Pale Rider 01-01-2015 09:45 PM

The bulk of the checks you did seemed to be resistance checks, when chasing these gremlins I usually do the easy stuff first as stated then I start at the plug, see if there is any spark using a number of diferent plugs that I have proven to work (test in another bike or even the lawn mower lol).

I then systematically look for voltage at each connection that supplies power starting at the stator. I guess you are kicking it so I would leave the plug out for these tests this way you are not fighting compression.
If there is no voltage at the stator then no voltage will be anywhere else to measure. If no voltage at stator i would open up the stator cover remove the magneto and inspect the stator, clean all pick ups and if you are able, test the stator coils. If voltage is found at stator connection then test at the next component that lead goes to, if no voltage then wires are sus. Continue until you identify the offending part. All this I do after wiring and connection clean and check.

Hope this helps.:cheers

LABRADOR Coaster 02-01-2015 06:19 AM

Thank you for taking the time to help me. You mentioned testing the voltage from the stator, do you know what the voltage should be?

In the meantime I will take a look at the other things you all suggested. Will let you know how it goes, thanks again.

Kero 02-01-2015 08:28 AM

While you have all your wiring out and connections apart, give them a bath in vaso so they won't corrode.

Pale Rider 02-01-2015 10:36 AM

Quote:

Originally Posted by Kero (Post 1895348)
While you have all your wiring out and connections apart, give them a bath in vaso so they won't corrode.

+1 :grinning-

Not sure for your particular bike, I dont think you mentioned what year it is (I could be wrong), your manual should tell you, thinking 12v. and should develop more as the magneto is spun faster. You could simply use a light bulb for this test, I have an old blinker I use for this, if it lights up bright its probably ok. You could use this initially to test if stator and CDI are conducting power or not.

I suggest you disconnect the kill switch for all of these tests like Kero mentioned earlier to eliminate a common issue and help you to find the real problem.

Keg 02-01-2015 12:27 PM

If you can see the spark it will be a carb prob. Try aerostart to see if it runs. Take it to a shop and spend the money on getting it fixed, not buying parts u don't need.

Do want sound like a smart arse but I have seen this in the workshop that many times it is not funny.

Kero 02-01-2015 07:28 PM

I thought so too Keg but the 530 I worked on last month had visible spark and enough for the bike to fire briefly, as soon as I unplugged the kill switch the spark went from a feeble one to a bright blue thing that went CRACK CRACK CRACK.
I knew I was on a winner straight away, and the bike was running moments later.
And yes, I had cleaned and tested the carby a number of times, and had my pilot jet change times down to less than a minute.


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