Is Jetting the solution?

maxrevs666

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#1
Ok, I have a 01 KX 125 fouling plugs fairly regularly. I am a novice rider so I suspect i am not pushing the bike hard enough to get the plug (BR9EG) into its heat range to burn off the deposits. I am about to change to BR8EG until i get a bit more confident with the bike (my first bike of any description) and feel confident with keeping it in the powerband (I am assuming that the powerband is where you open the throttle and the revs go high, higher then all of a sudden its HOLY SH1T!!!!! try to hang on!) The question I have is this: The bike is totally standard factory built spec - why would i need to play around with jetting, i am assuming it worked ok coming from the factory!, Now fair enough, wear and tear is expected on a six year old bike, but shouldn't a good tune up (repack exhaust, clean air filter, flush tank etc sort out any problem). Also changes in elevation is not an issue in this country per se.
Any thoughts are appreciated! :cool:
 

IndyMX

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#2
Most bikes come from the factory a tad rich.. It would be a good idea to address the jetting..

As for the powerband, Yeah, it's that Holy St!t moment.. You can try a set of Boyesen Pro Series reeds to help out with that. I use them in both of my bikes, and love them. They really mellowed the hit on my 125.
 

maxrevs666

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#3
That moment is what has me addicted , just looking forward to mastering it and getting my confidence built enough to keep the bike workin hard. I only have the bike a month and i wonder how i ever did without it! :)
 
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#5
ya you could try leaning out the air screw 1/4 at a time until it stops or starts bogging on ya, then def turn back rich until it runs right again, but 1/4 should clean up the running abit and will prolly help you quit foulin plugs, if that doesnt work, maybe address the jetting further, if not going down to a BR8eg so it will be a little colder running plug so it should help, personally i would rather run the correct plug and make sure the jetting is on spot....
 
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#6
lorollinls said:
if not going down to a BR8eg so it will be a little colder running plug so it should help, personally i would rather run the correct plug and make sure the jetting is on spot....
A BR8EG is actually a hotter plug than the BR9EG
 

maxrevs666

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#7
my understanding is that the plug number ie 8 or 9 dictates the heat range ofthe plug. this being that an 8 will reach operating temp at a lower level than the 9, thus burning off the deposits without so much hard running. but on the flipside it mau run too hot once running hard and cause preignition, damaging the engine. i have used a BR8EG for the last few days out on the bike, but this weekend I'll change back to the 9 as i feel confident that ill be able to keep the bike in the powerband more, now that i am getting used to it.
 
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#8
maxrevs666 said:
my understanding is that the plug number ie 8 or 9 dictates the heat range ofthe plug. this being that an 8 will reach operating temp at a lower level than the 9, thus burning off the deposits without so much hard running. but on the flipside it mau run too hot once running hard and cause preignition, damaging the engine. i have used a BR8EG for the last few days out on the bike, but this weekend I'll change back to the 9 as i feel confident that ill be able to keep the bike in the powerband more, now that i am getting used to it.
Yes you are correct except its not the 8 will get to temp faster necessarily, the lower the number (7,8,9 etc); the hotter the actual running temperature of the plug (tip). Thats why a BR8EG will likely work better while learning; it (the tip) will run hotter than the BR9EG and hence self-clean from deposits that can foul it.

If jetted rich that should be looked into (not familiar with KX125 to say) but while learning the hotter BR8EG will help the plugs last longer.
 
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#9
I ran an 8 in my former '01 KX125. It still fouled a plug every 2 months or so. When I switched from Maxima air filter oil (the blue stuff) to No Toil, no more fouling. I ran Maxima in my new 450F and it also fouled a plug. Switched to NoToil (when the new air filters came in) and been running for 8 months on the same plug. I noticed that both the KX and YZ fouled after starting with a freshly changed air filter (that sat overnight) so maybe I was over-oiling or maybe it was the oil, or maybe it was just gremlins.

I really liked my KX. It was a sharp turning, good handling bike. I'm thinking about asking the new owner if I can have it back!