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2006 YZ125 plug fouling and bog issue

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Hey there.  This is my first post on thumpertalk and ive decided to write this up because im having an issue and i cant seem to find any answers.  OK, so i bought my buddy's 2006 yz125 about a month ago.  I love the bike and take great care of it and keep up with all the maintenance. So here is my problem.  Ever since ive received the bike i have been basically fouling plugs every ride.  I've ridden the bike 7 times or so and ive got 7 plugs sitting in the garage. What would happen is the next day after the ride i would go to ride the bike.  It will start and idle fine.  I go to ride and as soon as i hit the powerband it bogs down and dies.  I would take the plug out put a new one in if i had one and it would be as good as new.  I asked my buddies about this problem and they said jetting and top end.  So i asked my friend who i bought it from and he said the top end could probably need a rebuild.  So i payed $86 for a new piston, rings, and gaskets (gotta love 2 strokes) and installed it.  No change, bike had the same problem but better compression.  So then i was told that i HAD to get a JD Jetting kit and that it will solve all my problems.  I live in Nashville, TN and the elevation here is only 600feet.  I bought the bike from my friend in Knoxville, TN and the elevation there is 885 feet so i figured that 285feet wouldnt really make a difference.  I proceeded to buy the Jet Kit.  Installed it according to the instructions with a 430 main jet and left the stock 40 pilot jet with the blue needle in the third position (middle).  Bike ran better but i go to ride it today and it does the same thing again.  Bogs on the powerband.  So i took the cyclinder head off and checked the power valve and all were working and looked fine.  after putting the bike back together all it does now is starts, revs high, and then dies. I double checked to make sure the throttle cable is routed correctly and it is.  When i would take out the plugs they are wet with gas.  Im using BR9ES plugs which is what the manual recommeds with a 40:1 mix with Yamalube. Ive got the air screw 2.5 turns out which is also the manual recommendation.  Bike also smokes alot compared to other 125s that ive seen.  Any help is greatly appreciated, just a newbie wanting to learn. :)

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It got worse after you disassembled the power valve? I would start there and check for wear. They can wear out and either stick open or closed. 

Also, how were your cylinder tolerances? 

 

Also, a leaner main jet may be in order.

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Bike smokes a lot?  Now unless it's the burning oil smell and smoke I'd check the crank seals and your gearcase oil. Usually when crank seals go the bearings do as well. 

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I would check your carb float hight first. There is a lot of topics on this. Definitely check your reeds for wear. Reeds on a two stroke get to be replaced more often than pistons. See if they are cracked or chipped and that they have plenty of tension. Try a BR8ES next time your are buying plugs too. The 8s burn hotter than 9s.

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55 minutes ago, Hudson Charlton said:

I would check your carb float hight first. There is a lot of topics on this. Definitely check your reeds for wear. Reeds on a two stroke get to be replaced more often than pistons. See if they are cracked or chipped and that they have plenty of tension. Try a BR8ES next time your are buying plugs too. The 8s burn hotter than 9s.

Ok will check the float height and reeds. I checked them a couple weeks ago and they were fine. Also will try a BR8. Does anybody prefer the iridium plugs over the cheap ones? I'm using standard ones but don't know if it's worth the extra $6 for iridium plugs. 

Thanks for the replies. Could it perhaps be the crank seal? I've seen some people mention this in other forums. If so how could I check or what is an indicator that it is?

Edited by j.mjr998

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39 minutes ago, j.mjr998 said:

Ok will check the float height and reeds. I checked them a couple weeks ago and they were fine. Also will try a BR8. Does anybody prefer the iridium plugs over the cheap ones? I'm using standard ones but don't know if it's worth the extra $6 for iridium plugs. 

Thanks for the replies. Could it perhaps be the crank seal? I've seen some people mention this in other forums. If so how could I check or what is an indicator that it is?

Iridium plugs aren't worth it imo. If a standard plug doesn't cut it, an iridium won't help your problem.

To check for crank seals, you have to do a leak down test and see if it drastically loses pressure.

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9 minutes ago, MaybeMe said:

Iridium plugs aren't worth it imo. If a standard plug doesn't cut it, an iridium won't help your problem.

To check for crank seals, you have to do a leak down test and see if it drastically loses pressure.

ok thanks. what is a leak down test?

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27 minutes ago, j.mjr998 said:

ok thanks. what is a leak down test?

Or do what I did. Drain every bit of the gearcase oil you can, put in 750cc exactly measures, then measure how much comes out again. If your short 200cc or more your sucking in your oil from there and the wet side crank seal is bad. If the dry is bad you'd get a lean effect by sucking in more air. 

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2 hours ago, Hudson Charlton said:

I did crank seals on a CR 125 because it blew the top end. It looked to me like the cause because it had been running so lean. Did you happen to check what brand of crankshaft you have while you were rebuilding?

I did not check the brand. The plan for today is to get a BR8 plug, clean the carb, and I'm switching oils. I'm trying Koltz super techniplate oil. Fully synthetic compared to semi synthetic. Most people say they don't like yamalube so maybe that will help. Also would like to note that the gas I was using wasn't very fresh.

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I did not check the brand. The plan for today is to get a BR8 plug, clean the carb, and I'm switching oils. I'm trying Koltz super techniplate oil. Fully synthetic compared to semi synthetic. Most people say they don't like yamalube so maybe that will help. Also would like to note that the gas I was using wasn't very fresh.

Do you remember if it was black or brown?

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Try 40:1 with a different oil.

I've always used Walmart SuperTech oil mixed with 93 pump gas and I've never fouled a plug for the three years I've been back on two strokes.

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Changing the premix ratio, going to a hotter spark plugs etc. are all band-aid cures for a bogging/fouling engine.

 

2-stroke engines are simple with very few moving parts but, ALL it's components must be within spec to run 'clean'.

In tune, even at 32:1 it won't spooge / foul plugs.

 

-fuel level (you set the TMX38 carb by actual measured fuel height, not the float's height)

-good reeds (not 3+ years old but they 'still look okay', they're a wear item just like a ring)

-proper jetting for the usage (pilot jet and needle can easily require going 2+ steps leaner if you ride at anything slower than a MX track pace)

-choice of low flash point premix (meaning not using a 'racing' premix for trail/off-roading where combustion temps are lower)

-good crank seals (confirmed with a crankcase leakdown test)

-fresh top end within specs (piston to bore, ring end gap, plating still serviceable etc.)

 

Also, a clean air filter, fresh gasoline, fresh silencer packing, not re-using fouled/cleaned up plugs all make a difference.

 

But in some cases no matter how well tuned,

a high strung motocross race bike just isn't well suited for slow trail riding and will load up no matter what.

Edited by mlatour
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Do you let it idle to warm up? 125s use 9 heat range plugs not 8. As your warning it up don't be afraid to hold wide open for second or two. do that few times will not hurt it. Cleaning it out before you ride could solve your problems.  And don't be lugging it around get on the gas :ride: I'd stick with yamalube if that's what bike is use to nothing wrong with that oil lots use it

Edited by Motox367

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59 minutes ago, mlatour said:

Changing the premix ratio, going to a hotter spark plugs etc. are all band-aid cures for a bogging/fouling engine.

 

2-stroke engines are simple with very few moving parts but, ALL it's components must be within spec to run 'clean'.

In tune, even at 32:1 it won't spooge / foul plugs.

 

-fuel level (you set the TMX38 carb by actual measured fuel height, not the float's height)

-good reeds (not 3+ years old but they 'still look okay', they're a wear item just like a ring)

-proper jetting for the usage (pilot jet and needle can easily require going 2+ steps leaner if you ride at anything slower than a MX track pace)

-choice of low flash point premix (meaning not using a 'racing' premix for trail/off-roading where combustion temps are lower)

-good crank seals (confirmed with a crankcase leakdown test)

-fresh top end within specs (piston to bore, ring end gap, plating still serviceable etc.)

 

Also, a clean air filter, fresh gasoline, fresh silencer packing, not re-using fouled/cleaned up plugs all make a difference.

 

But in some cases no matter how well tuned,

a high strung motocross race bike just isn't well suited for slow trail riding and will load up no matter what.

Thanks for the input dude. Will take some of this advice.

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17 hours ago, j.mjr998 said:

ok thanks. what is a leak down test?

Several threads on this. Search engine not the best, but if you use Google with the subject and the word thumpertalk it will find what you need. Here's a good one.

 

 

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