KDXRIDER.NET

So I got done doing a top end rebuild this weekend, and noticed a noise in the expansion chamber I never noticed before. When I rev the bike with no load, it makes a sound like something bouncing around inside the pipe while the engine is decelerating. I didn't notice it while riding it during break in, just when free reving from idle. It's an fmf gnarly desert pipe. I do not have much 2 stroke experience, is this normal?

heck no it's not normal. pull the pipe off and let what ever is in it come out.

And check your KIPS valves.

The noise is from combustion, just to be clear. I'm just not sure if it's a "ping", or just a common sound from the tin can sounding fmf pipe. It sounds crisper in general, I just want to be sure this isn't what pinging sounds like. It's the typical deceleration sound with a couple noticibly louder " TING TING TING's"

Check to make sure that the pipe isn't touching the frame.
Sounds can get amplified if it is.

Also, check to be sure the kickstarter end is not touching.

Negative on both kickstarter and frame contact. I'll try to figure out how to post a vid later when I get time. Then you guys can hear it and see if I'm just being over cautious. But until then, here is how I am tuned.

45pj
Needle in middle position
158 main jet
Boyesen 607's.

Air temps have been low to mid 40's

Need to know your altitude, otherwise your jetting information is useless.

600-700 feet

You just did a top end, so your compression is likely much better than previously. You didn't mention what ratio you are running or what a plug chop looks like. Could be a bit lean.

I'm running 50:1 premix. I have not had a chance to do a plug chop yet. After break in I did run it hard a little bit and it did feel a bit lean. Bogged a bit on the bottom at times after running hard.

50:1 is pretty light on the oil for a KDX. Just IMO and all. 50:1 seems to be fine for some folks.

Julien D wrote:50:1 is pretty light on the oil for a KDX. Just IMO and all. 50:1 seems to be fine for some folks.

That was going to be another question. I ran 40:1 before. After much reading on the web I decided to go 50:1 because the general consensus was its fine for trail riding. And I figured once gas got old enough I don't want to put it in the bike, I can just run it through the chainsaw, weed eater and blower since they all burn 50:1. However I am probably going to go back to 40:1 in the KDX for peace of mind. Right now I run Klotz TCW3 premix. What premix gets the popular vote amongst you folks?

Ed5786 wrote:...What premix gets the popular vote amongst you folks?

Lol, that's one of those questions you don't ask without starting a pages long discussion...

As long as it's 2 stroke oil, and you stick with the same brand/same ratio you'll be fine. Change anything and you may have to rejet. IMO I agree with Julien that 50:1 seems light, but lots of guys on here run it with no issues. Same with 32:1 (OEM recommendation) lots of guys run it (including my dad in his 94 which has had exactly 0 issues in its lifetime), though it seems my 220 smokes way too much at that ratio. 40:1 is popular because the math is easy Just pick one, jet to it and then stick with it.

Hate to tell you, I have religiously used AMSOIL Sabre 100 to 1 for 35 years in every application you can name without any problem. I always break in new engine as recommended by mfg. then go to Sabre AMSOIL.

Ed5786 wrote:

Julien D wrote:50:1 is pretty light on the oil for a KDX. Just IMO and all. 50:1 seems to be fine for some folks.

That was going to be another question. I ran 40:1 before. After much reading on the web I decided to go 50:1 because the general consensus was its fine for trail riding. And I figured once gas got old enough I don't want to put it in the bike, I can just run it through the chainsaw, weed eater and blower since they all burn 50:1. However I am probably going to go back to 40:1 in the KDX for peace of mind. Right now I run Klotz TCW3 premix. What premix gets the popular vote amongst you folks?

Did you rejet when you switched to 50:1? And is it the same compression piston as you had before?
My 91 was really loud and had a ringing coming off the pipe. 20 hrs later I had a hole in the piston.
...make sure you keep your rads full...

"Fun Wheel Drive"

Friedom wrote:

Ed5786 wrote:

Julien D wrote:50:1 is pretty light on the oil for a KDX. Just IMO and all. 50:1 seems to be fine for some folks.

That was going to be another question. I ran 40:1 before. After much reading on the web I decided to go 50:1 because the general consensus was its fine for trail riding. And I figured once gas got old enough I don't want to put it in the bike, I can just run it through the chainsaw, weed eater and blower since they all burn 50:1. However I am probably going to go back to 40:1 in the KDX for peace of mind. Right now I run Klotz TCW3 premix. What premix gets the popular vote amongst you folks?

Did you rejet when you switched to 50:1? And is it the same compression piston as you had before?
My 91 was really loud and had a ringing coming off the pipe. 20 hrs later I had a hole in the piston.
...make sure you keep your rads full...

"Fun Wheel Drive"

I did not rejet, other than the pilot and needle. It had a 42 pilot, and I went to 45. And I raised the needle one clip. I just bought this bike a little over a month ago. The previous owner also mentioned it has a BEP needle, not sure if that's much different than the stock needle. I may just order a DEL since that seems to be a popular choice. Or, just order a JD jet kit since I don't really have much time to tinker and experiment getting the jetting correct for different conditions.

Ed5786 wrote:

Friedom wrote:

Ed5786 wrote:
That was going to be another question. I ran 40:1 before. After much reading on the web I decided to go 50:1 because the general consensus was its fine for trail riding. And I figured once gas got old enough I don't want to put it in the bike, I can just run it through the chainsaw, weed eater and blower since they all burn 50:1. However I am probably going to go back to 40:1 in the KDX for peace of mind. Right now I run Klotz TCW3 premix. What premix gets the popular vote amongst you folks?

Did you rejet when you switched to 50:1? And is it the same compression piston as you had before?
My 91 was really loud and had a ringing coming off the pipe. 20 hrs later I had a hole in the piston.
...make sure you keep your rads full...

"Fun Wheel Drive"

I did not rejet, other than the pilot and needle. It had a 42 pilot, and I went to 45. And I raised the needle one clip. I just bought this bike a little over a month ago. The previous owner also mentioned it has a BEP needle, not sure if that's much different than the stock needle. I may just order a DEL since that seems to be a popular choice. Or, just order a JD jet kit since I don't really have much time to tinker and experiment getting the jetting correct for different conditions.

So you made the mix richer with a larger PJ, and you made it richer by putting less oil in the fuel (50:1 instead of 40:1), and you made it richer in the midrange moving the needle up one clip. Was the bike at a different altitude/location before the rebuild?

"Fun Wheel Drive"

No I bought it local

Then that seems like a lot of change to to fuel/air ratio. Plug chops?

"Fun Wheel Drive"