KLX 331S glowing-red-hot exhaust outlet pipe - possible causes?
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Thread: KLX 331S glowing-red-hot exhaust outlet pipe - possible causes?

  1. #1
    Senior Member kj7687's Avatar
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    Angry KLX 331S glowing-red-hot exhaust outlet pipe - possible causes?

    I've had this big bore kit on my bike for about 2,500 miles. Although it is a slight possibility that this issue could have occurred previously, I highly doubt I would have failed to notice it in well over 2 thousand miles of riding in many different conditions. I have only noticed a two or three times in the past week or two...the exhaust pipe (header/outlet pipe) sometimes will start to glow red-hot. I remember two specific times during which I noticed this problem. The first was after the bike had been sitting idling for about 3 minutes (I've done this plenty of times before and don't remember ever seeing that happen); the second was on my way home from school today. It was dark outside and I could look down and see my pipe glowing orange (more orange actually, not really cherry red as the title says...) from right where it comes off of the cylinder head back to about 2 or 3 inches from where it connects to the muffler. I was cruising at about 65 as I normally do, and it was staying orange like that. I got off the freeway a couple minutes after noticing that and slowed down a fair bit for surface streets; the glowing went away pretty quickly after that, but then I sped back up again to 55-60 mph and it started glowing orange again. Anyway, I have a few simple hypotheses...most of them involve PITA diagnostic work which I really don't have time for right now!

    *Low coolant (the overflow tank is at the normal level and the radiator has been verified-full)...

    *Some debris or something caught in one of the coolant passages, causing hot-spots

    *Water pump not working (it's a mechanical pump on a practically new bike...can't be this!?)

    *Something stuck in the exhaust causing excessive back-pressure (I checked the header and don't see anything. But I do hear a quite-slight metallic pinging sound if I shake the [stock] muffler back and forth fairly vigorously [as though a piece of metal inside is moving back and forth about 1 mm] - worth noting is that I noticed this with the muffler when I first got it and put it on the bike. It could possibly have worsened. It may be no problem at all...).

    *exhaust valve sticking open slightly due to malfunctioning Kawasaki Automatic Compression Release on that exhaust valve (broken spring on this part, maybe???)...?. But I didn't notice any power loss or poor running conditions; wouldn't this cause those? Maybe not?

    *Extremely excessive exhaust valve clearance(s)...same as above...? +I checked them 2,500 miles ago during big bore installation and all were well within spec - perfectly in the middle, in fact.

    *excessively rich or lean air/fuel mixture (this seems fairly unlikely to me since I haven't messed around with any of that since I did the initial setup after the big bore, and the bike hasn't been sitting for a long time. I didn't see any big tears in the carb intake boot or anything like that, and I can't imagine my air filter is missing or something lol... even if there were a problem in this area, it seems that if it were drastic enough to cause my header to glow orange, it would also cause running/idling/performance issues...?) EDIT: I have the OEM a/f screw (I think...), but could vibration have caused it to loosen a freakin junk load of turns and totally throw off the mix? Guess this is next to check...

    *header is just too small for big bore (but again, I'm 98% certain I've not had this problem until about a week or two ago)

    *bent/kinked/twisted/tweaked header, or possible cracked near the mounting point and/or not seating evenly where it mounts to the head??? Or an exhaust leak where it connects to the muffler (I did have to tweak the pipes slightly at that point to get everything to line up right, since the muffler was bent in a little on its mounting tabs that hold it to the frame [from a drop several months ago]...). I didn't notice anything obvious on any of this though...




    That's about all I can think of right now. I'm getting really sick of this crap; I just want to ride! And I don't have time to mess around with this shit every damn day - seems like I have been lately! Any input on my ideas or any other possibilities...all very welcome. Thanks much in advance!
    Last edited by kj7687; 09-11-2014 at 02:42 AM.
    KJ, just KJ, ok.


    Current rides:
    2004 GMC Sierra 1500, 1999 Toyota 4Runner

    Past rides: 2015 Yamaha XT 250, 1997 Suzuki DR 200, 2007 Honda Ruckus, 2007 Yamaha TW 200, 2007 Kawasaki Ninja 500, 2009 Kawasaki KLX331S; 1994 GMC Sierra 1500, 1987 Nissan Pathfinder, 1992 Acura Integra, 1986 Honda CRX, 1989 Jeep Cherokee, 1994 Chevrolet Astro Van, 1979 Volkswagen Rabbit, 1984 Jeep Cherokee

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    Senior Member kj7687's Avatar
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    I just checked my air filter and it does seem very dry; even when i squeeze it, absolutely no oil at all is left on my fingers... I used this "synthetic water washable" air filter fluid crap from "Rock Oil" that I bought from Parts + Accessories + Performance = ProCycle. Maybe this stuff doesn't work very well? Maybe it needs to be applied every 500 miles? Water is getting in there somehow when it rains? IDK...but it seems somewhat feasible that this dry filter could be causing a leaner air/fuel mixture, in turn causing my hot orange header, especially if my jetting is already borderline (almost too lean). Maybe I'll turn the fuel screw out 1/2 turn (richer) and also buy a new filter (use some god damn conventional filter oil this time...). I guess I'll try this and report back. In the meantime feel free still comment.
    KJ, just KJ, ok.


    Current rides:
    2004 GMC Sierra 1500, 1999 Toyota 4Runner

    Past rides: 2015 Yamaha XT 250, 1997 Suzuki DR 200, 2007 Honda Ruckus, 2007 Yamaha TW 200, 2007 Kawasaki Ninja 500, 2009 Kawasaki KLX331S; 1994 GMC Sierra 1500, 1987 Nissan Pathfinder, 1992 Acura Integra, 1986 Honda CRX, 1989 Jeep Cherokee, 1994 Chevrolet Astro Van, 1979 Volkswagen Rabbit, 1984 Jeep Cherokee

  3. #3
    Senior Member Xracer's Avatar
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    My KLR headpipe glowed from a too lean mixture. A bigger main jet did the trick. Also you will need to check the pipe is flush with the head and yes perhaps a dry filter can cause a problem.

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    Super Moderator littletommy's Avatar
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    Too lean.
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    Member Animal's Avatar
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    You didnt mention what your spark plug looks like. If I had spent the bucks for a big bore kit though , I would have changed the exhaust also. Balance everything! Then check your compression to be sure you didnt mess up the valve. Good luck!

  7. #6
    Senior Member Leben's Avatar
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    I will echo what others have said. It sounds like it is too lean.

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    Senior Member docjekyll2002's Avatar
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    My TW pipe was glowing red one day when i ran 91 pctane and the rpms kept staying high. I thought the pipe was gonna burst.

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    Senior Member troll's Avatar
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    I think it has been said... likely a lean condition. It is fairly common for header pipes to glow orange particularly when running hard.

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    Senior Member Werloc's Avatar
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    Ditto, to lean. Have you looked a your plug yet? That should tell ya right away...
    Bob

    When in doubt, Gas It..!!!

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  11. #10
    Senior Member Werloc's Avatar
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    Quote Originally Posted by Xracer View Post
    My KLR headpipe glowed from a too lean mixture. A bigger main jet did the trick. Also you will need to check the pipe is flush with the head and yes perhaps a dry filter can cause a problem.
    Your correct, but not about the filter being dry. All the filter oil does, is help trap dirt to filter. With the filter oiled, the dirt will stick to filter before passing through. But, and over oiled filter will not flow as much, but it's not that much of a difference. Oiled filters have to be checked and cleaned more often than a dry one.
    Bob

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