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General Tech Bad spark plugs

tinman58

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I now have about 200 miles on the new TR250. Doing a little carb adjusting, the engine is missing at higher rpm's. So I keep playing with the mikuni carb's. I have never worked with them before. I could not get rid of the miss. I decided to check spark, turn's out there was a bad spark plug. This is the second time this has happened on this car. I replaced all the plugs with new ones and the car runs great. How often do spark plugs go bad? Can the coil fry a plug?
 

toysrrus

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Dan,

What plugs were / are in it?

Russ

PS: I'm running NGK plugs now with about 2k mi. "200mi" is ridiculously low! I initially had Autolight plugs as a temp. & they self-destructed, literally!
 

bnw

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Always use the plugs the factory used to design and dyno test the engine. In your case, that would be Champions. When you've chased that mysterious missfire back to the "right plug, wrong brand" enough times, you will stick to that rule. Autolights, in my experience, are the worst offenders. Also, after years of "professionally " tuning two strokes, NGK plugs have the most accurate heat ranges and are possibly the best plugs out there. Heat range in a high strung two stroke can make the difference between gas fouling and a hole in the top of your piston if you are only one number off. If your 250 engine has been upgraded with a cam, intake, exhaust, higher compression, etc, then find the heat range in NGK that gives you the best plug reading at a full throttle high speed run (key off, neutral, coast to a stop) and stick with that.
 
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tinman58

tinman58

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I am using champions. Rn 14y . If there is any more problems I will go to NGK.
 

poolboy

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14....That's a fairly hot plug. Is that the recommended heat range ? I don't think it is...
...Maybe you should try Champion RN12yc or the slightly cooler RN9yc...or the equivalent NGK
If this is the second time a plug in the same loction failed, though, it's probably not the spark plugs fault.
 
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tinman58

tinman58

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Rn12yc is. What the specks say. I will get the NGK plugs equivalent to the rn12yc.
 

sp53

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I think the plug wires also have a lot to do with the plug. If you have a Nappa store close by, ask them for a generic set for a V8 or 6 made of metal. They usually have them, but might have to order them from their warehouse.
 

George_H

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Your problem sounds like a problem I had "back in the day". I had a 73 tr6 at the time, Every 2 weeks it would fry a plug. Didn't matter the brand. Turned oud it was a SMALL intake manifold leak. I assume the leak made the plug run super hot until it failed.
 
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