2 strokes, plug ratings, help!

[Dingledoo]

I've just bought a 2008 KTM EXC 125. It's my first experience of 2 strokes, the only other bike I've owned is a DR-Z250 (I'm a novice rider), so it's a bit different. I absolutely adore the KTM - so much lighter and more agile and much easier to handle.

However the first couple of rides I have fouled the plug (I was riding it just like it was a 4 stroke). I'm learning to adapt my riding style (ride it like you stole it as my husband says) but find it difficult to ride it on the pipe in in tight stuff.

I'm still not sure I'm running the right plug and fuel. I had been advised to run 98 octane fuel at 40:1, and have tried the following plugs: BR9ES and BR9ECMVX. I was under the impression that the higher the number the hotter the plug. But having just read an article in dirt rider about a rider with a CR125; advising a no 7 plug and 91 fuel to avoid fouling. The article states that the lower the number the hotter the plug. I'm now really confused - any advice would be much appreciated, cheers.

[B0000M]

on ngk plugs the lower the number the hotter the plug. if you're really putting around then this will foul a plug, but 2 strokes shouldnt just foul plugs when ridden slowly- this is usually caused by a poorly jetted bike

[vr4king]

NGK plugs=the lower the number the hotter the plug
Champion=the higher the hotter(i think i always run NGK)

I used to run br8es's in my cr125 was to scared to try 7
You can run br8egv's to which are alot more expensive i bought one but never used it as i didnt wanna foul a 30 dollar plug

I still have a few plugs left over from my cr pm me if you want them i can send em to ya

[avgas]

Sounds more like your issue is away from the plugs. What jets you running? I have run the crappiest plugs on smokers and still not fouled them.
Try running a 50:1 mix if you are riding low revs. Or using synthetic oil.
Also when did you last look at your air filter?

[Dingledoo]

Thanks for your replies. That's made it much clearer. Thanks vr4king for the offer of your spark plugs - but not to worry as I have a BR8EG which I shall try now that I know it's hotter.

What can go wrong if I were to use a plug that is too cold?

[Dingledoo]

Sounds more like your issue is away from the plugs. What jets you running? I have run the crappiest plugs on smokers and still not fouled them.
Try running a 50:1 mix if you are riding low revs. Or using synthetic oil.
Also when did you last look at your air filter?

I'm not sure what jets I have? This sounds very girly but I wouldn't know where to start taking my carburetor to pieces to find out. I think I may try a 50:1 mix (am using fully synthetic oil). The bike's manual states a 60:1 mix which I did use for my first ride, but I managed to still foul it using that (did take longer to foul), although I think that was also due to an over oiled air filter.

The last ride (40:1 with BR9ECMVX) was with a very clean filter, but I still fouled it.

[t3mp0r4ry nzr]

I would run what the factory manual outlines, 60:1 and I assume BR9 plug (?). If you are fouling on that, I would suggest leaning out your air screw/going to a smaller pilot, and/or dropping your needle a clip or two, depending on where in the throttle zone it is running rich.

If you just go with a hotter plug ie BR8, it may run hot enough to burn off the oil and not foul but the plug may be black with carbon soot from running rich - not ideal.

stick with 98 and ideally br9 plug and lean out the low end and/or mid range jetting. this should be safer than running a hotter plug and rich jetting.

im open to correction if Im wrong, but have had the same issues trail riding 125's.

[t3mp0r4ry nzr]

What can go wrong if I were to use a plug that is too cold?

colder the plug the safer for the engine in general. but easier to foul as temperature will be lower.

hotter the plug the more opportunity for engine damage. hotter plug meaning hotter than standard issue.

[Pierce]

I'm not sure what jets I have? This sounds very girly but I wouldn't know where to start taking my carburetor to pieces to find out. I think I may try a 50:1 mix (am using fully synthetic oil). The bike's manual states a 60:1 mix which I did use for my first ride, but I managed to still foul it using that (did take longer to foul), although I think that was also due to an over oiled air filter.

The last ride (40:1 with BR9ECMVX) was with a very clean filter, but I still fouled it.

Wow i'm surprised you are fouling up on all these fuel ratios. I usually run 40:1 on my CR250 and thats with a BR8EG, never fouled a plug once even when I was running 30:1.

Sounds to me like your bike needs to have its carb settings tweaked in a big way. Do you put round in low revs? I find when I've been putting round I will just squirt the throttle a bit to clear it out. NEver really had any issues with fouling though.

[t595]

Probably not a good idea to run a 125 at 60:1, run it like you have been at 40:1 with 9 plug.it shouldnt foul with that mix. get the jetting looked at.

[Crisis management]

Probably not a good idea to run a 125 at 60:1, run it like you have been at 40:1 with 9 plug.it shouldnt foul with that mix. get the jetting looked at.

Wot he said....KTM says run 60:1 or up to 40:1. I run 40:1 without problems.
Just a thought....Is your air filter clean? If it is really badly gunged up that will give a rich fuel setting...otherwise:

As others have said, your carburetor jetting is probably incorrect and needs setting up by someone that knows what to do, contact a bike shop / mechanic (I have no suggestions) to do this for you.
If you don't know who to contact you could try the bike shop in Thames (Wheels of Thames?) and they may be able to suggest someone local.

[avgas]

There used to be a fantastic race oil - Motul 8000 or something....really expensive, but good at cleaning out a 2-smokers system. Try a litre of that for a change.

[t3mp0r4ry nzr]

As others have said, your carburetor jetting is probably incorrect and needs setting up by someone that knows what to do, contact a bike shop / mechanic (I have no suggestions) to do this for you.

agree, take it to someone who knows what they are doing. a new pilot jet costs less than one of them flash spark plugs you are fouling and the jetting can be sorted fairly quickly if they are onto it.

[vr4king]

The less oil you mix in the richer the bike gets as its getting more fuel

IE 40:1 is leaner than 50:1

But id put money on it being jetting too id take it to someone who knows what there doing i had the same issues on my cr125 and i got it nailed eventually but took me months and lots of plugs

In the end all i had to do was raise the clip on the needle which in effect drops the needle deeper into the carb esetially allowing less fuel to pass and leaning it out

Oil to fuel ratios are 99% of the time NOT the problem with fouling plugs
Tests have shown the more oil the more power you get from increased ring seal

I would have no problems putting a hotter plug in but i certianly wouldnt go more than one heat range out of manufactures specs.

God why did i buy a 4 stroke

[Danger]

As above less oil will mean more fuel passes through the jets faster, making the mixture (fuel, air) richer. This will only make your situation worse.
Put the stock plug in, I would use Motul 800 at 32-1 on a 125 and check the airscrew setting or take it to someone who knows about jetting. As the weather warms up the bike will run richer, so it maybe jetted for winter and the airscrew adjusted, you will probably need to drop a size on the pilot, needle clip may need to be raised a position and a one size smaller main may need to be fitted.
You will also need a clean filter not over oiled and a freshly packed muffler would not hurt.

Confused now by all the conflicting advice?
Once you know what jets are in the carb you might want to call Triple X Moto as I'm sure they will have jetted a few 125's for some of their customers and can send you the jets you need. You'll be wasting your time just changing plugs as they are usually the last reason a bike fouls, as is the slow speed the rider rides at. A correctly jetted two stroke will not foul plugs.