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2005 250 exc: frustrated w. excessive smoking & now sparkplug fouling

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Need help: Bought the bike 2 months ago & it was my first 2 stroke coming off a 1998 Honda XR 400. When I bought it it started fine, idled good yet smoked a lil too much. Most 2 stroke riders I've ridden with said it smoked too much (a few are all KTM 2 stroke riders/racers)... a friend checked the jets & everything is still stock... adjusted air screw, new sparkplug, new air filter & bike still smokes more than norm... the new issue its having is fouling out sparkplugs as its running too rich possibly?? It starts first kick every time... idles for a while... give it lil throttle twists (1/8th turn) then loads up & dies out.... just started doing this too & Im clueless as too what it can be. Any help is appreciated. ** Not sure if it matters but Im running the red spring in the PV & its turned it mostly. Thanks in advance.

 

could it be bad piston ring/piston... crankshaft seal, etc?

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to check the right side crank seal, u can check the trans oil and see if its low, if its low fill it and ride it for a while then recheck the oil, my bikes crank seal went bad it would smoke horrible but I never had the fouling plugs problem,

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Need help: Bought the bike 2 months ago & it was my first 2 stroke coming off a 1998 Honda XR 400. When I bought it it started fine, idled good yet smoked a lil too much. Most 2 stroke riders I've ridden with said it smoked too much (a few are all KTM 2 stroke riders/racers)... a friend checked the jets & everything is still stock... adjusted air screw, new sparkplug, new air filter & bike still smokes more than norm... the new issue its having is fouling out sparkplugs as its running too rich possibly?? It starts first kick every time... idles for a while... give it lil throttle twists (1/8th turn) then loads up & dies out.... just started doing this too & Im clueless as too what it can be. Any help is appreciated. ** Not sure if it matters but Im running the red spring in the PV & its turned it mostly. Thanks in advance.

 

could it be bad piston ring/piston... crankshaft seal, etc?

 

Stock jetting is your problem, stock KTM's run rich.  So while it's possible that it could be a mechanical problem (like low compression), it's more likely that your jetting is out to lunch (way too rich).  I personally would buy a JD jet kit, install that and then see if that fixes your problem.  I had to do that with my '12 300XC-w after fouling a couple plugs on one ride with the kids.  The JD jet kits really are easy to install, just read over the instructions in the house when you get the kit and decide on the jetting that your going to go with.  Do it again one more time when your in the garage installing their recommended jetting.

 

NOTE:  Just install what they say to install and set what they say to set.

 

That's what I did and now my 300 runs better than it ever did off the showroom floor (I was lucky and bought it new).  The kits can be sort of pricey ($75), but that's nothing compared to the ease of mind knowing that you'll never foul another plug!

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to check the right side crank seal, u can check the trans oil, if its low fill it and go ride it a while, if its not leakin oil and its low then the right crank seals bad, my right crank seal went bad and it smoked horrible but never fouled a plug, also if the seals bad check your crank up and down play when u have it apart, see if the bearings have play.

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Stock jetting is your problem, stock KTM's run rich.  So while it's possible that it could be a mechanical problem (like low compression), it's more likely that your jetting is out to lunch (way too rich).  I personally would buy a JD jet kit, install that and then see if that fixes your problem.  I had to do that with my '12 300XC-w after fouling a couple plugs on one ride with the kids.  The JD jet kits really are easy to install, just read over the instructions in the house when you get the kit and decide on the jetting that your going to go with.  Do it again one more time when your in the garage installing their recommended jetting.

 

NOTE:  Just install what they say to install and set what they say to set.

 

That's what I did and now my 300 runs better than it ever did off the showroom floor (I was lucky and bought it new).  The kits can be sort of pricey ($75), but that's nothing compared to the ease of mind knowing that you'll never foul another plug!

 

 

 First off I just wanted to say, "Thank You," to everyone who chimed in & offered advice, very much appreciated it. I fixed the problem today & the results were fantastic (so far). I knew it wasn't the crank seal as I check my tranny fluid often (just in case) & I'm not loosing any. My gut feeling was the carb (problem inside of it) as if something was clogged because the bike was just running very good last week. Anyhow (thanks Zig06) I also knew the bike was running much to rich. To start with, I took the carb completely apart & cleaned it thouroughly w. carb/choke cleaner. I next took out the needle & adjusted the clip (small piece on top of needle) to the top position (3rd down is stock setting according to manual & that's where it was previously set at). This supposedly leans it out. I next lowered the main jet from 160 (stock) to 155 (bought new for $3.) Put it all back together & started 2nd kick. Air screw out 1 turn only (stock setting). Put in a new spark plug & a clean air filter also. It idled fine & smooth but high (then adjusted). Then let her warm up & noticed how snappy it responded(as I flicked the throttle little amounts) & how much less it smoked. Then took her for a test ride. It honestly felt like a new bike!!! It was fast before but now it seemed scary fast & super snappy/responsive... also running the red, PV spring turned in a lot. The bike hardly smoked also. Again, it felt incredibly stronger. My only fear now is that its running too lean. The fuel mix is still 40:1. If anyone reads this just let me know if it sounds too lean & if I need to adjust before I cause some damage. Thanks again.

Edited by cheetah66

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what's your elevation? temperature? sounds pretty lean unless you're at like 7500 ft or higher or running in 100deg heat...  I have an 04 250 EXC and I'm at 1000 ft give or take - mid 60's to low 70's right now. Running at the recommended jetting and it runs awesome - no fouling plugs, minimal amount of smoke, always starts on 1st or 2nd kick when cold... when warm, 1st kick every time.

 

with your needle dropped and main jet at 155, you might not have yet noticed as the main jet and the clip position affect fueling near or at WOT... I wouldn't hold her wide open for very long if i were you (again, unless you're at high elevation or super hot conditions)...

 

something doesn't sound right... but I've only had my '04 for this season, so don't know enough yet on what else it could be...

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My elevation is approx 800ft. Temps are cooling off as summer is ending & fall starting...temp range 75f-50f. I had all stock settings before & it ran ok but smoked more than norm. Then recently it started bogging & dying out just as I would start out to ride (after warming up). There must have been an obstruction in the carb. though, that I removed w.carb cleaner. The guy I bought it from (elevation 1100ft) had a main of 145 & everything else was stock... yet it too smoked more than norm when he had it. I've only had this bike 3 months.

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Stock jetting is your problem, stock KTM's run rich. 

 

That's what I did and now my 300 runs better than it ever did off the showroom floor (I was lucky and bought it new).  The kits can be sort of pricey ($75), but that's nothing compared to the ease of mind knowing that you'll never foul another plug!

 

If the bike's main seals are in good condition, the stock jetting can work very well.  My KTM definitely ran rich on the needle when the jetting was set stock.. a local pro buddy of mine recommended setting the jetting to stock except making the needle one clip leaner, and then adjust the air screw until there's no blubber when twisting the throttle off the bottom RPMs. 

 

Also the FMF Fatty pipe and Powercore silencer help it run smoothly and clean.  No matter the humidity, temperature or elevation, my 300 sings without ever giving me jetting problems.  In fact I haven't had a single problem with my bike because I maintain it, and I always count on it purring on idle and screaming on top, just how I like it :)

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If the bike's main seals are in good condition, the stock jetting can work very well.  My KTM definitely ran rich on the needle when the jetting was set stock.. a local pro buddy of mine recommended setting the jetting to stock except making the needle one clip leaner, and then adjust the air screw until there's no blubber when twisting the throttle off the bottom RPMs. 

 

Also the FMF Fatty pipe and Powercore silencer help it run smoothly and clean.  No matter the humidity, temperature or elevation, my 300 sings without ever giving me jetting problems.  In fact I haven't had a single problem with my bike because I maintain it, and I always count on it purring on idle and screaming on top, just how I like it :)

Well said... & I esp. liked how you ended that.  Thanks for all of the info & advice. Im glad your bike is running strong & smooth. I got a lot of advice from these forums & have read many so far. This was the first carb. I ever took apart, never mind messing w.jets & a needle. Lots of youtube vids helped as well. Just to make sure I wasn't daydreaming about the bike running stronger, I took it out yesterday for 1.5 hrs. Same situation... running Fast & Strong... almost like it had a major tune up or something. A lot less smoking & VERY responsive. It reminded me of an old buddies CR250 motocross bike that was Scary Fast. I hope Im just not too LEAN... my clip is on the top of the needle & my main is a 155... pilot jet is stock 35, air screw out 1 turn. Also has a Pro Circuit pipe/silencer. The bike is sooooo much more FUN to ride now. Ok I better stop as Im still in awe of how its running. I will say my other buddy has the 300 like you own & damn I love that bike, the torque esp.... then when you throttle down, its like a MISSLE. That may be my next bike... as I used to ride an XR400 so I LOVE having torque down below & my 250 lacks it... yet makes up for it in so many other ways. The 300 seems like an awesome mix of everything to me. Anyhow, thanks again.

Edited by cheetah66
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Well said... & I esp. liked how you ended that.  Thanks for all of the info & advice. Im glad your bike is running strong & smooth. I got a lot of advice from these forums & have read many so far. This was the first carb. I ever took apart, never mind messing w.jets & a needle. Lots of youtube vids helped as well. Just to make sure I wasn't daydreaming about the bike running stronger, I took it out yesterday for 1.5 hrs. Same situation... running Fast & Strong... almost like it had a major tune up or something. A lot less smoking & VERY responsive. It reminded me of an old buddies CR250 motocross bike that was Scary Fast. I hope Im just not too LEAN... my clip is on the top of the needle & my main is a 155... pilot jet is stock 35, air screw out 1 turn. Also has a Pro Circuit pipe/silencer. The bike is sooooo much more FUN to ride now. Ok I better stop as Im still in awe of how its running. I will say my other buddy has the 300 like you own & damn I love that bike, the torque esp.... then when you throttle down, its like a MISSLE. That may be my next bike... as I used to ride an XR400 so I LOVE having torque down below & my 250 lacks it... yet makes up for it in so many other ways. The 300 seems like an awesome mix of everything to me. Anyhow, thanks again.

 

Talk to a local dealer, see what jets are recommended for your elevation, temperature and humidity.  That's the "stock" jetting I refer to with my KTM, but I run it 1 clip leaner on needle and adjust air screw accordingly.  You'll figure it out.  

 

One way to tell it's running lean is if you roll off the throttle and the motor makes a fast "nanananananana"  sound as the engine breaking slows you down.  If it's rich, it'll bog on engine breaking and not be so crisp when you crack the throttle to get off engine breaking.

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