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Spark Plugs Keep Fouling...

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Jun 25, 2010
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#1
Ok so I have been having trouble with my Cr125. It keeps fouling plugs. When I first got the bike I ran NGK BR9EG(thats what it says in the manual to run.) But they would last an hour or two at most. Then I switched to NGK BR9EIX Iridium plugs but I still foul them occasionally. I want to stop this problem soon because $10 for a spark plug is a lot! I am sure it is the carb but I do not know what to adjust in the carb! So any help would be greatly appreciated!
 
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#2
This is really something you need to learn how to do. It's simply too involved for someone to walk you through it via a forum. However, if you print out a guide and spend a day working on it, you will have it down.

PLEASE read this. Follow the steps. Ask if you have any specific questions.

http://www.kawasakimotorcycle.org/f...ing-guide-info-2-stroke-riders-must-have.html

If that one doesn't suit you, there are loads of jetting guides out there. Just do a quick search ;).

J.
 
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#3
Plugs foul because: The way you ride it, the way you set it up/jet it, and/or the way you maintain it. Do you have a manual?
 
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#4
Going from a BR9EG to a BR9EIX would do nothing to prevent fouling, it would only cause you to foul a more expensive plug.

Going from a BR9EG to a BR8EG would help prevent the plug from fouling and allow you to work on the jetting issues, which might be your issue.

A spark plug has a temperature that it needs to operate at in order to stay "clean" and healthy. If the plug gets too hot it can be damaged. If it doesn't get hot enough then deposits will accumulate on it and it will eventually foul.

The numeric portion of the spark plug "number" indicates the "heat range". This basically is a measure of how easily the spark plug can get rid of the heat. The higher the number, the more heat it can transfer out to the cylinder head.

If it transfers too much heat out, the plug gets too cold, doesn't burn off the deposits, and fouls.

The plug needs to be of a proper heat range, but the jetting needs to be proper as well. It would be unwise to fix the fouling problem by only changing the plug heat, but going to a hotter plug will make life easier for you while you sort out the jetting issues.

My suggestion: try a BR8EG plug. If you keep fouling, switch to a BR8ES, they are a lot cheaper.

Rod
 
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#5
My KX250 used to fowl plugs all the time when I first bought it, almost every ride I'd fowl one (I was also a beginner at the time and didn't know much). My problem was I'd let it idle often, like when coasting down hills, or talking to buddies, or whatever. Someone gave me the advice if its ever idling for more than a few seconds, give it a good rev. After starting to give those occasional revs, as well as harder higher revving riding in general I very very rarely ever fowl a plug.
 
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#6
Ok so I bought some BR8EG plugs I will see how they will work out. I will work on my jetting. Should I buy the JD jetting kit for 75 bucks. Or should I buy the jets, needles, etc seperatly?
 
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#7
Buy the jets seperately, they only cost about $5. each. I would buy 1 size larger and 1 smaller than what you already have.
 

BSWIFT

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#9
The jetting links at the top of this forum is all you need along with a spread of jets. Follow Spanky's guide to the letter and you will have your bike jetted properly and be able to tell when you need to change for varying conditions and how you ride the bike.
It is very important to start in the right place and make one change at a time. Insure you have a clean filter, fresh fuel, proper premix (regargless of the brand of premix), and no other problems. Your premix ration should be within the proper range of the oil. OEM's recommend 32:1 but many members run other ratios. I run 40:1 in all my 2 strokes and use my old premix for the weed whacker and chainsaw. Use an oil that is retilly available and in your price range. Stay consistant with your fuel and your mix. Most pump fuel varies so buy from the same place when you can.
Spanky's guide works. Read it thru before you start and keep it handy while you are doing it. I jetted my YZ250 5 years ago and still run the same plug. Granted I have not riden much in 3 years but the bike starts 1-2 kicks every time. Good luck and have fun.
 
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#10
what gas you running?
my nephews cr125r 2004 ran like crap when we got it back together.kept fouling plugs and boging at lower throttle to mid.
now it is running top notch
here is what we did to get it to run real good-
we bought 1 gallon 110 race fuel
we bought 1 gallon 89 oct cheap gas
mix 50/50 110 and regular unleaded fuel-runs perfect,use a very good 2-stroke oil.
i know his main is back to stock,and the needle is in the stock location to,we put a smaller pilot in i think but it may be at 40 stock i cant remember.
the manual for this 2004 cr125r says in big black letters-
USE 95 OCTAIN FUEL OR HIGHER
we were running cheap 87 or 89 octain from caseys general store and it ran like crap.
if you buy the 110 and mix it 50-50 with the cheap crap it will raise the octain rating of the fuel so the bike can run.
DONT GO TO THE AUTOMOTIVE PARTS PLACE AND BUY OCTAIN BOOSTER THAT WILL NOT WORK.
if you decide to take my advice do like we did,add the 50/50 mix then do a plug chop,if the plug looks on the rich side ride it for 10 min then look at plug again-looks good ride ride ride.
nephew has around 25 hours on this mixing on this bike all trail rideing
 
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#11
killer454 said:
the manual for this 2004 cr125r says in big black letters-
USE 95 OCTAIN FUEL OR HIGHER
The Honda minimum requirement is 95 RON not 95 pump octane. It's common for US fuel to have a 10 point spread between the RON and MON ratings (called the fuel's sensitivety), so some quick math (R+M) / 2 gives us:

( 95 RON + 85 MON ) / 2 = 90 pump octane or AKI

So essentially any pump premium (93-90) in the US will "technically" satisfy the minimum octane requirement of 95 RON.

Outside of the US the number at the pump is RON, so the numbers are larger but the fuel has the same basic octane rating when compared using the same test methods.

If mixing a race fuel and pump fuel made a substantial change in the way your bike runs something other than the final octane number was the cause. The change in the distillation curve of the race fuel is the likely cause not the higher octane.
 

Uchytil

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#12
Honda specifies a pump octane(owners manual) of 92 for my 01 CR125R while Yamaha specifies 95 RON (shop service manual) for my 1997 YZ125. Since both engines are stock form (more or less) they get pump premium which averages (like Rich stated) 90 pump octane. I would get that and jet for the conditions (temperature, humidity, and altitude). Pretty basic stuff, and, for me, I switched to a dual stage fiberglass reed system for the CR (EB type).
 
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#13
jdon88 said:
Buy the jets seperately, they only cost about $5. each. I would buy 1 size larger and 1 smaller than what you already have.

If he is fouling plugs he is not likely too lean, so I wouldn't buy anything larger.

Making a trip to the bike shop or paying postage for mail order will probably exceed the cost of a few jets. My suggestion is to buy at least four sizes smaller, then you should have one available if you ever go to a higher elevation and need to take it one size smaller still.

Rod
 
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#14
Ok I will check out Spanky's jetting guide. Does anyone know how many jets come in the JD kit and what sizes? Also I always run 93 oct. with Pro Honda HP 2 stroke oil at 40:1. I think my muffler needs repacking, should I do that before jetting?
 
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#15
DirtBiker125CR1313 said:
I think my muffler needs repacking, should I do that before jetting?
Your bike has to be in proper working order before you start jetting. Repacking the silencer is just one of the things that need to be addressed before you start.
 
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