Fried Spark Plugs!!!!


4 replies to this topic
  • BlueZoom

Posted November 21, 2007 - 01:43 PM

#1

I have an 03 Yamaha YZ450F and I keep frying spark plugs.

I put a new spark plug in and I ride for about 30-60 minutes. All of a sudden, when my bike gets hot, it starts blogging and cutting out to the point it quits running. It won't start immediately.

If I sit there for 5-10 minutes, it cools off enough for the bike to start right up. I ride it for 3-5 minutes and it does the same thing. I did this 5 times just to get my bike back to camp this last weekend.

Once I get the bike back to camp, I put in a new spark plug and it runs like new....for another 30-60 minutes.

I have done this 4 times so far.

I run a Big Gun CDI box in it and I have also tried it with the stock CDI with the same results.

I have read several other threads and can't find an answer that really nails this down. Anybody have any answers for this?

Could this be related to Octane of the fuel? I have ready several other threads that four strokes need 91 Octane. Embarrassingly, I have been running 87 octane, per a recommendation from a friend. I won't do that again.

  • grayracer513

Posted November 21, 2007 - 01:51 PM

#2

It's probably not related to the fuel, but that doesn't mean you should run regular. Any ordinary pump premium should be fine.

The bike is supposed to have a CR8E (or a variant of that. the CR8 is the important part) If you're running a CR9*, it will foul it quickly. 7's may cause pinging.

I don't trust the BG box; I've heard too much negative. If I had to guess, I'd say it sounds like the wrong plugs, but I don't know.

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  • sirthumpalot

Posted November 21, 2007 - 05:42 PM

#3

It could be fuel; is it hot and are you riding slow, as in slow enough to boil the fuel in the carb? According to a blurb in DirtRider some of the KXs were getting hot enough to boil the gas in the tank in some situations, so the pro mechanic for that team put heat shielding under the tank and on the carb.

My second thought is when it works fine cold but starts to get funny hot then guess #2 would be failing electronics somewhere. Maybe break out the electrical meter and test out your stator. Try to check it cold then again as quickly as possible when it starts to fail. Also possibly borrow the ignition box from a buddy with the same bike to see if that resolves the issue. I'm with grayracer, dump the BG ignition box, at least until you get the issue resolved. Definitely don't run 87 octane in the bike. I doubt it would cause your current issue, but it could put a hole in the piston if it's pinging enough.

  • todds924

Posted November 21, 2007 - 06:03 PM

#4

It could be fuel; is it hot and are you riding slow, as in slow enough to boil the fuel in the carb? According to a blurb in DirtRider some of the KXs were getting hot enough to boil the gas in the tank in some situations, so the pro mechanic for that team put heat shielding under the tank and on the carb.

My second thought is when it works fine cold but starts to get funny hot then guess #2 would be failing electronics somewhere. Maybe break out the electrical meter and test out your stator. Try to check it cold then again as quickly as possible when it starts to fail. Also possibly borrow the ignition box from a buddy with the same bike to see if that resolves the issue. I'm with grayracer, dump the BG ignition box, at least until you get the issue resolved. Definitely don't run 87 octane in the bike. I doubt it would cause your current issue, but it could put a hole in the piston if it's pinging enough.


I like the checking the stator idea.

  • BlueZoom

Posted November 21, 2007 - 08:58 PM

#5

I appreciate your input and will check the stator. Just as a note, I am running the CR8E spark plug, or 4 of them now. I will also try getting rid of the Big Gun CDI.

Thanks again!





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