DAMN Riders - No rules, Just ride!

I have a 2007 450 sxf that wasn't running very good at all when I bought it. The '07 is a standard carbureted model with electronic ignition. I removed the carb, removed the bottom drain plug and removed both the main and pilot jets. I also removed the mixture screw. I ran carb cleaner all through these ports and ended confident I had the jets opened up. I also filled the float bowl several times with carb cleaner, shook it up and drained it out several times. Cleaned it as best I could without taking the carb apart any more than I did (I cannot get a carb kit right now because of the holiday). I reassembled and reinstalled it all and set the mixture screw to 1-1/2 turns out from the full seated position. While I had it all apart, I also measured all valve clearances to within spec at TDC according to the service manual instructions.

Once done, it ran much better. It is especially easier to start now than it was before. Its still not running just right though. It does not backfire, but when I roll on the throtle it is making a crackling type of noise. Kinda like hundreds of small, mild backfire sounds. Hope that explanation makes sense. On deceleration it makes that same noise as well. Its got decent power but I feel like it shoud be offering more than it does. Just "feels" like a fuel issue to me, but I am not certain.

Hoping someone here can steer me in the right direction on this issue.

How's the air filter?

Stock exhaust or aftermarket?

Have you ever had a KTM before?
Is the fuel old?
Can you do a compression check?
Is the noise from the exhaust or from the engine case?
Is there a power loss?
Is the noise coming from the slide plate on the carb?

My guess is that it's the timing chain....which is super noisy on KTMs (at least all that I know of).

Air filter is new. It has aftermarket exhaust. My first KTM, New fuel, Noise from the exhaust. The only (odd) noise I hear from the engine itself is the timing chain noise - which seems excessive to me but the bike is not backfiring and my buddy with the same bike has the same noisy timing chain but his runs very well. It does seem to be lacking power somewhat.

It's not a rattle I am hearing. Its a crackling, misfire type of sound from the exhaust.

Could a clogged exhaust cause this? I do have new packing that came with the bike I could repack it with?

Has the jetting been changed to accommodate the aftermarket exhaust?

Sounds not cared for, might/probably needs rejetting and a valve adjustment.

bonehead wrote:Sounds not cared for, might/probably needs rejetting and a valve adjustment.

And we have a winner.......

Bike looks like a new one but yeh, you might be right not cared for but I ended up in this very cheap.

I also fully expected to find the valve clearance messed up the way it acted but as mentioned above, the valve clearance has been verified within spec at TDC. Intake was at .15mm, Exhaust was at .18mm.

I do not know if jetting has been changed from stock spec. Rejetting seems like the most likely new focus? Would this crackling be the result of an installed main jet too small or too large?

Small - too lean. Bog on the bottom. After market pipes normally need more fuel to support additional flow. Would assume someone on KTM talk would have proper jetting for your bike and exhaust posted. Also you have the MX bike so expect it to not idle perfect the cams will make it want to perform at WFO performance. Not a woods friendly choice.