cr125 -2006 loosing spark...

Hey,

I've got a Honda CR 125 -2006 with a weird problem... I start the engine up and it runs for a few minutes but then dies suddenly and I can not start it again.

I take the plug out and test it but I can not get a spark from it.

And here is the weird thing: I try the same plug on another CR 125 and can not get a spark from it there either..

The spark plug starts to give off sparks again if I let it rest for a few days.

I have two theories:

1. There is something wrong with either the coil or the CDI box that somehow destroys spark plugs.
2. There is something wrong with the fuel/air mixture that makes the spark plug seize to work for a while.

I'm leaning towards alternative no. 2 but would like to know if this is something that has happened to someone else or if anyone has any other theories regarding this.

It might be worth mentioning that this has started to happen about the same time as winter arrived here and I have not adjusted my carburator at all. Should I buy a bigger main jet and see if that solves the problem?

Thanks and a happy new year!!

Thanks for all the help!!

I 've tried doing as sharky243 suggested:
I took a new spark plug, filled the tank with fresh petrol premixed with high quality two stroke engine oil (ratio 50:1).

(I did have a low quality mineral 2 stroke oil in before and it was a higher ratio as well...)

I also took the carburator apart and cleaned it properly.

While I was at it I lowered the jet needle one step to get the engine to run leaner.

After I had put it all back together again I started the engine up (with the choke pulled out) I let it run on idle for a few minutes until I could push the choke in. I then did a few laps around the house and she seems to go fine now.

I need to test it out properly on the course this week, but it might have been that I had too much oil in the fuel in combination with not revving the engine high enough..

I'm a beginner so I don't let the engine run on as high rpm as it should.

Sounds like your plug is fouling. Does it look black or wet when you first pull it out after it stops running?

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Yes it does look black and wet. I will look at it after a few laps the next time I go out on the course and see if it did help.

Actually I should really buy a couple of main jets and do a proper tuning of my carburetor since I have never done it and I bought the bike in the summer (we get about 20 degrees C in the summer and -10 degrees C in the winter...)
Anyone know a good set of steps for tuning in the carb on a mx bike?

Do you oil your air filter when cleaning it?
I recently had the same problem - a mx mechanic told me contrary to belief, not to use oil at all as it constantly kills the plug. Since taking his advice I havent had the problem since but it might be worth making sure the filter hasnt been oiled too much.

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Yes I oil the filter... Everyone I know oils their filters.. Are you sure about that? sounds strange.. What about sand and dirt coming into the carburator?

Thanks for all the help!!