OOH-NOO Did my top-end go???

[Mountainman650]

Hey guys
I was riding today, with the family. My wife and daughter were on their 4-wheelers, so it was mostly just putt-putting around on some trails.
My bike was seeming to " load-up" a bit , so when we hit a nice wide open area ,I was hammer down... WOT, for a few passes back and forth , and all of a sudden the bike got REALLY loud from where the exhaust comes off of the motor(with some smoking), with a kind of slight metalic sounding ting to it??..???(hard to describe) with a slight loss of power.
Soo I shut her right down, for fear of damaging anything (worse).
I pulled the plug , and it has a light brownish color to it. The exhaust also had a slight "burnt" smell to it when it first made this noise...
93' KDX 250 by the way....
Ok guys ,Did I toast the top-end??????? Whats the easiest way to tell??
I have done some re-jetting lately , but I only went from 165main to 162.5 main and from 42 pilot to 40 pilot , the bike did run better with this jetting, much crisper throttle response, but could that of been the cause of this??? She was runnig a bit rich with the old jetting , so I wanted to make small adjustment in jetting ...????
Any Help is much appreciated!!!!!!!!!!!!!!
Thanks
Dave

[Indawoods]

Just sounds like your pipe got dislodged from the cylinder to me. Check to make sure your pipe is fully seated in the cylinder, that both O-rings are present and in good shape. And lastly, make sure you have all the exhaust springs.

[Mr. Wibbens]

I had the KIPS shaft retainer screw loosen up one time, that sure made some different sounds!

[IdahoCharley]

If you have been tooling around slow and then really work the engine hard and heat up the pipe hotter than it has been for a while - some weird smells can be emitted from the pipe and you can see some smoke emitted from the exhaust pipe even after you shut it down - based upon my experiences.

Don't have any answers related to the noise though. I would likely pull the pipe and look into the cylinder from the exhaust port to see if visibly piston surfaces and visible cylinder surfaces looked normal. Maybe like Indawoods said - just a dislodged pipe - springs good? O-rings still good? Pipe hangers good and tight?

[canyncarvr]

re: 'with some smoking'

..that smoke coming from the cylinder/pipe joint?

Then you either heated some goo or you blew a hole in some previously deposited goo.

If the topend was damaged, you would see it on the plug...like little sparkly bits of aluminium? THAT would be a bad thing. Still maybe not fatal...but not good for sure.

The best way to 'make sure' as Inda says is to take the pipe off, clean it up and check the fit. With the S/A off it's not too hard to fit the pipe and observe the fit of the pipe neck into the cylinder. If it don't fit square, use a couple of levers (floor jack handles, pieces of pipe) to tweak it back into place (pipe off the bike, 'adjust', refit, repeat until it's right.

Yeah...keep a close eye on the S/A fit while you're doing that. If the pipe 'fits' and then the stinger has to be moved 2" to mate with the S/A...then the pipe doesn't 'fit'.

Most seizures will leave evidence on the exhaust side (hot) of the piston.

If the plug is good (no metal bits on it), then the piston crown is OK. If the exhaust side of the piston is good, then consider the pipe fit.

Once it's all cleaned up, put the pipe back on with a good-sized bead of hi-temp RTV at the pipe/cylinder joint.

If your exhaust gasket falls out, don't forget to put it back in. If you don't HAVE one (someone left it out earlier), get one. My preference is to include that part because:

1. It's supposed to be there.

B. It acts as a cushion between the pipe flange (nickel steel) and the cylinder (wimpy cast aluminum).


Likely not something to worry about (the smoke/noise...not referring to the gasket).

[Mountainman650]

Hey guys
Thanks for all the great responses.
I think the dislodged pipe theory might be the ticket.
I pulled off the pipe tonight and the piston and cylinder look good,
looking through the exhaust port.there is a bit of spooge built up around the
exhaust port, on the outside around the pipe. So the o-rings/springs could be worn,
I have no idea how long they've been on there. I ordered up a set of o-rings/spring kit from my local off-road shop, it's from FMF, for about 8-9 bucks....
The gasket inside the flange looks ok. I'm not sure if this comes in the FMF kit,
but it looks more like CanyonCarver said ,a cusion for the two dif metals, so it should be ok....CC, are you putting the bead of high temp sillycone on the outside joint of the pipe/flange -after the pipe is on , or are you saying to put it in by the o-rings before putting the pipe in.????
Thanks again guys, this site is the best!!!
Dave

[m0rie]

Put it between the two orings and then just install the pipe.

[Indawoods]

I wouldn't be a bit suprised if you find you have more responsive bike when you get it buttoned up! An exhaust leak on a 2 stroke is a bad bad thing......

[canyncarvr]

re: goop

What m0rie said.

Putting it on after the fact would not be at all effective.

Try to clean the cylinder out some, too. Use some kerosene to clean up the inside walls of the port...follow with alcohol. Give the RTV something to stick to.

You didn't say if there was exhaust smoke coming from the pipe joint. If so, realignment of the pipe is most certainly something that should be done.

Oh...don't put the pipe on with the RTV...let it sit overnight...then tweak on it to make the S/A match up. That will ruin the seal you made.

Make sure everything matches up first...THEN RTV it, get the springs and hangers on AND the S/A on...before the RTV sets up.

Don't start your bike until the RTV cures. If you have a goodsized miss-fit, you'll just blow the stuff out. A worklight hung close will help (heat).

IF you are going to try the realignment part...go slow. It take very little tweak to the header to make a BIG change to where the stinger sits, how the hangers line up, etc.

[Indawoods]

How'd it go Mountainman????