I need advice setting up the carb on my 2005 450 EXC (KTM). The bike is running like crap (for the first 20 minutes when cold). Stock jetting was 178 main, 42 pilot, 85 mid with an OBDMR needle and that combo was considered lean. Bike was rejetted by previous owner at 200km (JD kit???) to 150 main, 48 pilot and OCEMN needle (clip at 4th position). Other than cleaning the carb, that jetting combo and accelerator pump settings are untouched and the bike has always ran awesome until this summer.

The bike starts and idles well enough, but black smoke (lots) comes out the exhaust upon acceleration and bogs huge and almost dies. It also has flames shooting out the back upon fast acceleration. I roll the throttle back to ¼ and it smooths out nicely. I’ve played with the air mixture screw between 0 and 2.5 turns out...still lots of black smoke. I suspected a plugged main jet (not getting gas resulting in bog) so I removed the jets, soaked them in lacquer thinner and reinstalled. Same problem. Spark plug is black and oily so it’s running rich. I’m no expert on the intricacies of a rich condition, I just know it’s rich. So it’s getting too much gas at full throttle even on that tiny 150 main jet (go figure). However, after about 20-30 minutes of it bogging at throttle, the problem goes away TOTALLY and it runs great.

So I suspected the valves. When I checked them, exhaust hadn’t moved since the rebuild in May 2008 (still at 0.005”). Intake valves, one was very loose, one was very tight. They hadn’t been adjusted since the rebuild but they are on spec now. Started bike...same black smoke, but it did start easier with the intake valves in spec. Now I’m back to the carb! Accelerator pump???

Bike has stock exhaust system and 4500km on it. Top end was rebuilt at 3000km (May 2008) due a valve adjuster nut coming out loose and grinding everything. Bike ran great after the rebuild up until 700km ago. Worn needle? Accelerator pump setting?

If the fuel/air mixture screw doesn't seem to adjust it enough, which position should the needle be to lean it out (it's on 4 now). Other advice??? Does the needle position adjust it lots and the A/F screw for fine tuning or are they independent and unrelated?

Help! (and thanks).

hello i need advice on the radiator because i just replaced the top end and all but i made sure i tightened all of the bolts really tight. and my 1991 suzuki rm 80 wont hold anifreez. like i ride for not even 10 minutes and its already out and i got fast so that air can get through the radiator and i tightened all the radiator hoses so i cant figure out why it is leakeing. please help!!

Yes, it was fairly sudden (not in one day) but over a few rides. This was 700km ago (20 hours) and I've just lived with it since. Oddly enough, every once in a while when I take it out it, it doesn't happen.

Here's the update. I figured I'd try to go to the far extreme and really lean it out, then go back and find a happy medium later. First thing I did was pull the spark plug, clean it, gap it and re-insert.

Attempt 1. Using all the same jets and needle, move the aftermarket needle from position 4 to 3.
still black smoke. Note: bike started in one half-ass kick and it's NEVER done that before!!!

Read the KTM manual and it says the needle can wear at 200 hours, resulting in rich condition....so.....

Attempt 2. Replace the aftermarket needle with the stock needle (which is rumoured to be too lean on all KTM forums), set the clip to position 3 (one leaner than stock). A/F screw 1.5 turns out. Should be really lean now right? Black smoke.

Attempt 3. Using same hardware as Attempt 2, turn A/F screw all the way in - should be really lean now right? Well, a little less black smoke, but still some.

Attempt 4 - beer and bed. Gave up.

Now let's say it is late ignition, I have NO IDEA how to work on that. But you guys are right...jetting shouldn't change so I guess I may be going back to how it was, then looking into late ignition. Can ignition timing change and "wear down" or is it fixed forever.