Why are the plugs fouling so fast?


I'm getting between 150-200 miles out of a spark plug - is that normal? (this is my first 2t)

I read the thread about why 2t's smoke and someone posted that too much gas in the cylinder will foul plugs. Isn't it the oil that fouls the plugs?

If it's too much gas that's causing the problem, can I change the mix from 50:1 to 40:1 without changing the jetting, or will that cause excessive smoke?

It's an 07 ktm 200 xc-w (great bike!). It's running on a 50:1 synthetic mix. The pilot jet was moved from 42 to 40 and the needle clip was moved up one position. Except for the plug issue, it runs great. Thanks. :cool:


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Going 40:1 will make it smoke worse. I would think that 50:1 would be as lean a mixture as you would want. Are you put-putting around all the time or do you wind it out? Other than that, you may need to take a look at your jetting.


Going to a 40:1 mixture probably isn't going to make it smoke one bit more. Both mixtures are lean on the oil. And it will lean your jetting slightly, but probably not enough to fix your problem. I agree with above statement that if you a doing a lot of slow riding, you might need to rejet and readjust needle to lean it a bit.
But really, if you like the way it runs, putting a spark plug in it every 200 miles doesn't seem that bad.

50:1 is really lean isnt it

i agree try going to a 40:1

and 200 miles isnt bad my friend's old bike only got like 2 hours (but the thing was messed up soooo.....)


I ride typical New England trails - fairly tight woods, tree roots, rocks, etc and a small pit area. That's why the bike is so great - it's light and handles really well through the tight stuff. The area I ride is not that big, so I don't always have it pinned. I 'putt-putt' sometimes. Is that really bad for a 2t? I ride about 65 - 70% on the throttle and the rest just cruising.

Does the plug just 'foul' at any time? So far it's only happened when I went to start it in my garage. What would happen if I was going up a fairly steep hill in the pits? Would it just stall halfway up the hill?


You should post a picture of one of the fouled plugs. Usually, going up hill gets the plug hot enough to keep it clean. Bikes don't usually foul plugs during climbs. What oil are you using? What heat range is the plug?


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If you do a lot of slow speed trails, the best thing I have found is to use either platinum or gold spark plugs. They stopped my fouling problems on a 97 KTM200EXC, and I do a lot of tight trails, and slow riding. Just ask the people that keep trying to get around me so they can move above a snails pace :ride:

I also have run 40:1 since I bought the bike new in 97

if u say it only fouls in your garage, i wouldnt worry when you are actually riding it because like somone else said when your climbing a hill the plug is hotter because you have a load on the motor causing it to work harder and thus getting it hotter. so if u say it is running good and it is only fouling plugs in your garage and not really after you ride it i wouldnt worry about it at all


40:1 and 50:1 is an oil mixture. Lean and rich is gas/air mixture. Don't confuse the two. If you are jetted for 40:1 then leave it that way. Changing the oil ratio to 50:1 when you are jetted for 40:1 will make the bike run RICH. Jet it for the mix you are currently running.


personnaly, i think 50:1 is way too lean. i would switch it to 32:1 and jet it according to that. as long as your not putting it on trails you should be fine running 32:1, it offers more protection than 50:1, so when the time comes to run it to the bone to passs someone you can be safe knowing that your bike is not going to seize.


Three tales of plugs and fouling:

I have a two stroke outboard, 9.9 HP. In the 15 years that I have owned the outboard I have changed the plug once. I run 50:1 oil mix, whatever oil is cheap. The motor gets used a fair amount, and it always is operated under fairly heavy loads and up in the higher RPM range. It starts easy and will idle without stalling.

I run 40:1 synthetic oil (Motul 800) in my YZ-125. I have never fouled a plug to the point that it wouldn't run, but when I ride along with my wife on her quad I tend to "putt" and the responsivness of the bike just goes to hell. Every once in a while I have to get up and go for a minute or else it will start bogging so bad I can't stand it.

One of my riding buddies rides a Yamaha WR-250, two stroke, same oil mix, same plug. He has never had a problem (that I am aware of) when we were riding together. A couple of weeks ago we rode together in a club enduro, family oriented event. The enduro runs several loops, reusing previous sections a bit. They stagger the end points, sending the masters the farthest and the novices stopping the earliest. Once the deadline for the last rider has passed we all ride the course backwards, pulling all the arrow stakes and removing the ribbon from the bushes. It was a lot of slow riding, frequent stops, never getting up to speed.

We made it about two miles before my buddies bike just quit from a fouled plug.

If you want the performance from a two stroke then you need to work the engine hard enough to burn the deposits off the plug. If you are willing to "detune" (like my outboard is) then run a hotter plug it will tolerate putt'in around, but you will lose that peak performance.



Thanks for all your suggestions. I'll try the better plugs rather than mess with the jetting. There's houses near where I ride so I want to keep the smoke (and noise) down to bare minimum. :cool:


So where do you get these platinum spark plugs? I did a google search but can't find them for the ktm. My dealer is over an hour away so I'd just as soon buy them online. Thanks.