CR 125 Plug fouling!

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May 5, 2007
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#1
I've got a 96 CR125 that constantly eats plugs up. I've had it at 2 shops where they insisted it was a fuel problem and overhauled the carb. They've tested the stator, the coil has been changed, and still the bike fouls a plug after a 1/2 hour of riding. The plug is a nice chocolate color but with not an ounce of spark left. You can immediately throw another plug in it and go for another 1/2 hour. Oh and the crank seal has been replaced on the flywheel side. Anyone have any ideas?
 
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#2
Are you maybe not revving the motor out enough? 2-strokes are known for fouling plugs if you dont keep them wound out most of the time.
 
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#4
If the plug is brown, it is getting hot enough to clean itself. I don't think the problem is due to jetting or lugging it around. My bike was doing something similar. The plug would appear to be ok but it wouldn't spark. It actually was sparking, if you looked inside of the plug and kicked the bike over. It would arc between the insulator and the side of the spark plug, deep inside. It wouldn't cross at the gap so it appeared the plug wasn't sparking at first. I went through two plugs before I changed the right side crankshaft seal. I haven't been through one since.
 
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#5
76GMC1500 said:
It actually was sparking, if you looked inside of the plug and kicked the bike over. It would arc between the insulator and the side of the spark plug, deep inside.
Sounds like a fouled plug to me!

dcoperator:

I certainly wouldn't suspect the carb on a plug fouling situation. Having the float level too high could cause a fouling situation but anything related to the carburetor getting "dirty" would make it run lean, not rich. It is possible that the jetting is just plain wrong, however.

I would try going to a one step hotter plug and see what that does for you. Either that or ride it harder, two strokes don't like to putt.

Rod
 
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#7
This happens to me too, and I have a CR125R as well.
I doubt its the brand of the bike..
I keep mine wound up all the time, and it still fouls a plug once every few hours.
Someone told me the solution would be carb-tuning (jetting).
It's jetting a little rich, would that cause the problem. (plug is moist and black)
Crankshaft seal isn't a problem on my bike, it's brand-spanking new.
Any tips?
 
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#8
THORmx_nucca said:
It's jetting a little rich, would that cause the problem. (plug is moist and black)?
Yes. That is the most common cause of this condition.

Of course, that would be too easy in my case recently, so I had to re-split the cases because I did not get the right side seal seated correctly the first time I rebuilt the lower end.
 
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#9
THORmx_nucca said:
Crankshaft seal isn't a problem on my bike, it's brand-spanking new.
Your bike has TWO crankshaft seals. The left side might be new, but the right side might not be. Even if the right side is new, if the shaft sleeve for the seal is worn, it will still leak. Worn main bearings can also cause the seal to leak. Keep an eye on the oil level in your transmission. If you lose any oil between changes, the right side seal needs to be replaced.
 
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#10
try klotz oil- 40:1- change the silencer packing material- if there is oil drooling out the head ,and silencer- you want a brown color,not dark chocolate,set the float level so fuel doesnt fill the bowl more higher than the over flow tube,
check the tranny oil level- if its burning tranny oil it could be from the right crank seal,or the center case gasket,
also check the reeds- i use the carbon fiber series - there a little more cash but well ! worth it
klotz is great oil it burns cleaner than other oils ,reduces carbon build up, and doesn't foul plugs like other oils
 
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#11
What is your fuel:oil ratio? you can try running a hotter plug so it will burn more of that carbon.
 
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#12
My fuel ratio is 32:1 and I've already tried a BR8 but didn't like the grey color of the plug after a short ride.
 
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#14
A 35 pilot,420 main,needle in the middle,air screw 1 3/4 out.Now how many 125's fit that jetting spec for 400 feet above sea level and 60 degrees fahrenheit.That was still a little fat on bottom,but not by much,when it warms up it will be perfect!That was a 02 cr134,and cr125 stock jetting was a 400 main and 37.5 pilot..I am going to ditch the mikuni and get a 38 keihin!If your bike is not able to run on those settings,then I would say you have other issues than the seemingly grey area of jetting!