Wr426 exhaust is melting airbox..Has hot exhaust.


10 replies to this topic
  • dirtbikekid1

Posted August 01, 2007 - 05:52 PM

#1

My 2001 wr426 exhaust is running so hot it is melting a hole in the airbox and the headers are glowing red. I tried re-jetting with a 195 main, 50 pilot, and adjusting my needle jet on the 5th notch. What could be the problem? I heard the Wr's run really hot, but to melt my plastic it must be a problem. What can I do to fix this? Thank you so much for any help.

  • Mutu

Posted August 02, 2007 - 12:32 AM

#2

Is it the stock exhaust?

  • dr x

Posted August 02, 2007 - 02:49 AM

#3

It must be nearly touching for it to melt a hole in your airbox....doesn't sound like its the right pipe for your model, My fmf Q2 off my yz 426 will just about fit on my wr 450 but the fit is bad and touches in places it shouldn't...

The stock pipe has loads of clearance

  • GCannon

Posted August 02, 2007 - 08:14 AM

#4

A plugged exhaust will make things (exhaust system) run hot since the hot gas will not escape as fast and heat wants to go somewhere. You may want to disassemble your exhaust can and clean all screens. It may also be a good time to repack with new packing material.

I don't know what is up with your jetting but if those jet sizes you gave are correct you must be really rich! Maybe fuel is burning in the exhaust and that might be where the extra heat is coming from (just a theory).:eek:

Have you read all the "Sticky notes" at the top of this forum check them all and look at the Jetting Database for similar bike setups. good starting point.:thumbsup:

  • dirtbikekid1

Posted August 02, 2007 - 11:10 AM

#5

Thank you all so much for the input! I do not have a stock pipe. I currently have a FMF #S3000. I think it is too close too the box though. I also have a GYTR pipe. Should I put that pipe on or the stock pipe? I'll also try re-jetting leaner too. Thanks again..

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  • Just_a_trail_rider

Posted August 02, 2007 - 04:00 PM

#6

Its hard to imaging you running a 195 main. Did you mean a 165. I run a 168 on my 450 with an FMF pipe and I think its about right.

Get some heat wrap if you need to. Aluminum foil is the poor man's trick for building a heat shield. That's what they use on the other side of the plastic side plates. Try it, it works if you can stand the look of it.

  • Mutu

Posted August 02, 2007 - 06:12 PM

#7

Thank you all so much for the input! I do not have a stock pipe. I currently have a FMF #S3000. I think it is too close too the box though. I also have a GYTR pipe. Should I put that pipe on or the stock pipe? I'll also try re-jetting leaner too. Thanks again..

Ok. Sounds like you have no packing in them mate. Are they excessively loud?
No packing would definately explain the extreme heat, poor performance and lack of response to jetting changes.

If you gon't want to repack them yourself (easy job) then your dealer would do it for you for a few bucks.

Expect a quieter bike that would make a lot more power! :ride:

  • ccoates445

Posted August 02, 2007 - 09:47 PM

#8

"No packing would definately explain the extreme heat, poor performance and lack of response to jetting changes."

Spot on.:applause:

  • GCannon

Posted August 03, 2007 - 01:44 PM

#9

I don't understand why would no packing would mean more heat?
I could see if the packing material leaving the muffler collected on the spark arrestor screen causing an obstruction.
I just don't understand how no packing could cause excess heat build up. wouldn't no or less packing material allow additional area and or additional volume for hot gases to escape the muffer more quickly?

Hopefully somebody can straighten me out.:excuseme:

  • Mutu

Posted August 03, 2007 - 10:31 PM

#10

First up, with out the packing, there is no insulation for the can, and with exhaust temp up to and over 700*c, it gets hot! :eek:

How it effects performance, the extra volume creates problems with the sonics of the whole system, and you can get pressure going back up the pipe (like a 2-stroke). FMF has had great success with doing this to the head pipe though. The extra volume also disturbs the exhaust flow out of the pipe. This in turn creates problems for scavenging effect. :thumbsup:

  • ccoates445

Posted August 03, 2007 - 11:14 PM

#11

I don't understand why would no packing would mean more heat?
I could see if the packing material leaving the muffler collected on the spark arrestor screen causing an obstruction.
I just don't understand how no packing could cause excess heat build up. wouldn't no or less packing material allow additional area and or additional volume for hot gases to escape the muffer more quickly?

Hopefully somebody can straighten me out.:excuseme:

Packing not only quiets thing substantially, but also insulates the outer skin from taking on too much of the exhaust heat passing thru and puts it out the tailpipe. Mutu makes a good point on back pressure and sonic dynamics. packing plays a bigger role than most would think.




 
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