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Cr125 killing spark plugs every 15mins

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Posted (edited)

Hey guys, I have a 2003 cr125 I bought a couple weeks ago and I'm having a problem with it. The spark plugs die every about 15 minutes, with hotter plugs it will last about 45 minutes. I herd that if the timing is off it can over heat the plugs and burn out the the resistor. Is there any truth to that? The reason I thinks it's not fouling is because when the plug dies it gives no spark no matter how much you clean it, And it shorts out. 

Edited by Randomneewb

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Sounds to me the plug has fouled. Is it wet and black? Your jetting is to rich or your reeds are worn and need replacing.

few things to consider 

1 how long ago was the top end refreshed

2 how old are the reeds

3 do you have a manual ? If not get yourself one because you will need it to keep this bike maintained 

 

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Ok thanks! I'll take a look at the jetting when I get home. This is what the plug looks like btwIMG_1327.thumb.JPG.f31bf79f7b113615b547a400be358f89.JPG

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Posted (edited)
9 minutes ago, Randomneewb said:

Ok thanks! I'll take a look at the jetting when I get home. This is what the plug looks like btwIMG_1327.thumb.JPG.f31bf79f7b113615b547a400be358f89.JPG

That plug is fouled for sure. The black stuff is soot, which makes it impossible for the spark to jump to the electrode. 

If you scrape it off with a steel brush or flat screwdriver you can sometimes make them work again. Sometimes you never get it to work again (due to grounding it itself). 

Check your reeds and jetting. :thumbsup:

Edited by Christoffer Brandel

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Posted (edited)

Take a peak at the gearbox lubricant level, has it noticeably dropped since last checked?

If so, combined with your fouled plugs it's likely a sign your RH side crank seal is allowing gearbox lube into the crankcase.

 

Once you've ruled this out, before any attempts in fine tuning the jetting you must confirm the float is adjusted to specs.

Edited by mlatour
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I'm using 32/1 for the fuel right now. Yeah that plug in the picture is recommended for the bike. 

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If the bike ever ran well with the jetting you have, it's NOT the jetting.

You have a failing crank seal sucking in trans oil.........or a nearly complete loss of compression due to over-worn rings.

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Ok so update, I was having some top end noise so I took a look and found out that I have some scoring on the cylinder, being a big noob with two strokes I dont know how much this would effect fouling. Whats your option?  

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I'm using 32/1 for the fuel right now. Yeah that plug in the picture is recommended for the bike. 

Try 40:1.

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How dirty is the air filter? (I read noob) I’ve seen new guys run an air filter thinking it’s like their car. Filter could cause fouling if they are filthy

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Posted (edited)
12 hours ago, Randomneewb said:

Ok so update, I was having some top end noise so I took a look and found out that I have some scoring on the cylinder, being a big noob with two strokes I dont know how much this would effect fouling. Whats your option?  

 

Of course there is the question on how the OP actually rides this bike,

this is a full-on / wide open throttle high performance MX race bike.

It can be slow trail ridden but, will require fine tuning to match that usage but...

 

as KRAN mentioned, if that engine ran good before and now all of a sudden it fouls plugs,

it is not jetting or premix ratio related but rather a mechanical issue, either something is worn out or damaged.

 

Attempting to lean out the jetting, going to a hotter plug or, changing the premix ratio will only

mask the problem and since diagnosed improperly will likely cause more damage.

 

It's a 15 year old MX race engine with an unknown past maintenance history,

it's common wear items and service shedule is measured in hours of use, not years of use.

At the very minimum it will need a look over by someone experienced in 2-strokes

and a good refurb (top end, reeds, carb clean, packing, crank seals etc.) before any attempts in fine tuning.

Edited by mlatour
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The first thing I didn't to the bike was to get a new air filter and oil it so it pretty clean. I haven't had this bike very long so I don't know if it ever ran for more than 15 minutes with 32:1.  Is there any way the check the jet to see if it's stock? I is there any numbers I should be looking for?   

Thanks for all the imput guys!

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15 minutes ago, Randomneewb said:

The first thing I didn't to the bike was to get a new air filter and oil it so it pretty clean. I haven't had this bike very long so I don't know if it ever ran for more than 15 minutes with 32:1.  Is there any way the check the jet to see if it's stock? I is there any numbers I should be looking for?   

Thanks for all the imput guys!

Yeah on the jets there is going to be a stamped marking with a number. That is the size.

Sometimes if jets are very old they can wear out some and become larger than stated. Happens mostly to the main jet.

Also check the needle tip. It goes in the main jet and may have som wear to it too which makes it let in to much fuel when closed.

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