2006 CR125 fouling plugs constantly

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12/5/2018 4:11 PM

Hi guys,

I have a 2006 CR125 that is constantly fouling plugs. I'm using the BR8 (the hotter plug.) I live in North Carolina so we are at sea level. I moved from New Mexico ay 6,000 and she ran like a champ. Never had a problem with fouling plugs. I did a top end rebuild before I moved; piston, cylinder, and cylinder head and she ran great. Then I moved to sea level and always fouls plugs. I'm using a 410 main, 37.5 pilot (I did change the jets when I moved and the main and pilot are BRAND NEW genuine Honda parts so they're not clogged), and the second need clip position 32:1 ratio with amsoil dominator oil and 93 non-ethanol. I can ride it for about 20 minutes and it pulls hard and feels amazing. Then 5 minutes of putting around she shuts off. Every time the plug is wet and black. I started getting some oil shooting out the exhaust so I changed the right crank seal, stopped the oil problem. BUT it still is having the same plug fouling issue. My next plan of action was to do a resistance test of the stator. If you guys have any other ideas or checks please feel free to comment. I've also cleaned the carb and replaced the reeds with boyessen reeds. Not sure what else to do before looking into the electrical system. Thanks!

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12/5/2018 4:43 PM

The 5 mins of putting around is likely the issue. 2 strokes are wide open or off. Try leaning out your pilot circuit and maybe look into the needle.

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12/5/2018 5:11 PM

maybe replace the oring on the seat, number three on the picture
carb

if it barely leaks the extra fuel heads towards the cylinder instead of out the overflow and it will be slightly rich

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12/5/2018 5:26 PM

Hey Gavin this is Wackerbarth from Albuquerque. Glad your still riding man!
Those jet sizes should be close to what you need. Do a plug test right after your 20 minute Moto and see if your burning a lite chocolate color. Also check your float height. What needle are you using? See if you can find the number on it.

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12/5/2018 5:57 PM

speed_racer wrote:

maybe replace the oring on the seat, number three on the picture
carb

if it barely leaks the extra fuel heads towards the cylinder instead of out the overflow and it will be slightly rich

Cool thanks I'll give that a shot.

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12/5/2018 6:01 PM

JWACK wrote:

Hey Gavin this is Wackerbarth from Albuquerque. Glad your still riding man!
Those jet sizes should be close to what you need. Do a plug test right after your 20 minute Moto and see if your burning a lite chocolate color. Also check your float height. What needle are you using? See if you can find the number on it.

Hi John, long time no see! Little blast from the past lol.
I've been checking the plug every time it foulds and is straight black and wet. i'll find the picture and post it.
I'm not sure on the needle, I havent changed it, only the position. I'm in the middle east right now so i wont be able to check the needle until next month sad

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12/5/2018 6:13 PM

JWACK wrote:

Hey Gavin this is Wackerbarth from Albuquerque. Glad your still riding man!
Those jet sizes should be close to what you need. Do a plug test right after your 20 minute Moto and see if your burning a lite chocolate color. Also check your float height. What needle are you using? See if you can find the number on it.

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12/5/2018 6:13 PM

Thank you for your service young man!. I'm glad your doing well. Yes as soon as your back check the needle/seat condition and type also the float height. I really don't think you have an electrical problem. But I've been wrong once before so anything can happen!

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12/5/2018 6:21 PM

JWACK wrote:

Thank you for your service young man!. I'm glad your doing well. Yes as soon as your back check the needle/seat condition and type also the float height. I really don't think you have an electrical problem. But I've been wrong once before so anything can happen!

Thank you, I appreciate it. The needle and seat looked to be in good condition. I wonder about the float as well. Might be letting too much fuel in. I'm making a list of trouble shooting ideas to check when I get back. Any recommendation for what the float should be set at?

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12/7/2018 8:07 PM

Just my 2 cents. I have an 07 CR125 and also knew somebody that bought one brand new and remember him having an issue fouling plugs since day 1. My 07 seems much more prone to fouling plugs than my old yz125 or any other bike I have owned for that matter. For what it's worth they don't seem to like being ridden at lower RPM and just seem really finicky bikes to set up for different conditions.

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12/8/2018 8:44 AM

My Guess would be it needs a new carb. I had similar issues with 2 CR250’s. I put an air striker on one and a Lectron on the other. They both run perfectly now.

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12/8/2018 12:51 PM

My son's 07 was the same way. The bike came from Honda jetted way rich. The previous owner wasn't too proficient and made it worse. We got a JD kit with the bike, and after installing that it was much better. After a few further small adjustments, it runs clean and strong (ours has a PC pipe and silencer). My 250 started running poorly and I attribute it to crappy ethanol gas sitting in the carb over the winter and a blown out silencer packing. Cleaned the carb, replaced the packing and it runs like brand new. I'd go ahead and replace the float jet, as someone mentioned. Ethanol eats the rubber o-ring at the base of the jet.

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12/9/2018 6:19 AM

" I moved from New Mexico ay 6,000 and she ran like a champ. Never had a problem with fouling plugs. I did a top end rebuild before I moved; piston, cylinder, and cylinder head and she ran great."


Simpel, go lower on the main.if the main is right then you can play with the rest. There is moreee then enuff oil on the spark thats for sure. So mixing to much oil or you ride it not hard enuff. Or try 40:1 or try a different oil

A 85 and a 125 will foul plugs right away if the jetting is to rich and you don't burn it but cruising with the bike.

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12/9/2018 10:22 AM

The main is definitely too rich stock. I don't remember the stock jetting specs but it sounds like your present set up is close to them.

One of the issues with the stock jetting is the taper of the needle. The JD kit supplies two replacement needles and overall jetting specs (and jets) covering a range of conditions/altitudes. The kit absolutely cleaned up my son's bike. It was so rich when we bought it that the original owner had installed a super hot lawn mower plug to get it to run. (Glad we discovered that right away).

Good luck.

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12/9/2018 7:39 PM

JMCR250 wrote:

The main is definitely too rich stock. I don't remember the stock jetting specs but it sounds like your present set up is close to them.

One of the issues with the stock jetting is the taper of the needle. The JD kit supplies two replacement needles and overall jetting specs (and jets) covering a range of conditions/altitudes. The kit absolutely cleaned up my son's bike. It was so rich when we bought it that the original owner had installed a super hot lawn mower plug to get it to run. (Glad we discovered that right away).

Good luck.

The stock main jet is a 430 (which is insanely rich), 55 pilot, and the third clip position. Do you think I should try going leaner on the main and pilot as well? Maybe a 400 or a 390 for the main? And maybe a 32.5 on the pilot? The JD kit seems to show it supplies both of those sizes which is nice. I'll have to look at the needle number when I'm available to do so as well.

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12/10/2018 9:34 AM

Pro Circuit suggests 410 with a 50 pilot, stock needle in position 2.
https://www.procircuit.com/jettingspecs2.htm#2006

MXA suggests 440, a 27-67 needle in position 3 and a 50 pilot.
https://motocrossactionmag.com/2006-honda-cr125-test/

Stock is a 430 with a 55 pilot. Honda's jetting from the factory may be rich, but not that rich.

If you're running a 37.5 pilot and fouling plugs, there's a mechanical issue. Start with the right side crank seal.

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12/10/2018 10:27 AM

Matt Fisher wrote:

Pro Circuit suggests 410 with a 50 pilot, stock needle in position 2.
https://www.procircuit.com/jettingspecs2.htm#2006

MXA suggests 440, a 27-67 needle in position 3 and a 50 pilot.
https://motocrossactionmag.com/2006-honda-cr125-test/

Stock is a 430 with a 55 pilot. Honda's jetting from the factory may be rich, but not that rich.

If you're running a 37.5 pilot and fouling plugs, there's a mechanical issue. Start with the right side crank seal.

Right side crank seal has already been changed. Float level is my next check.

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