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  1. #1

    Will a clogged CAT CONV burn a piston?

    I have a question related to melted/burnt pistons
    When I bought the 2000 XL1200 ltd (pv motor) ski it had a melted piston.
    I just put three new jugs and pistons. post re-build, ski ran fine. I ran 50:1 mix gas, kept it below 4000rpm. Every now and then though if I held 4000rpm, the exhaust buzzer would go off. Stop ski, let cool go again. This went on for 1/2 the tank. Also every now and then the ski would just die (like pulling the chicken strap) at 4000rpm.

    Today, it died hard. When i got home I pulled the head. Had a dang melted piston. But not the same one that was originally melted. Checked the cat. It was blown out and logged in the stinger. (Note when I first rebuilt the engine it was in the same place. Not knowing the machine, i thought that was where is was supposed to be. So I thought that was normal until I looked at the parts breakdown DOH!!!) YUP grown man crying here.

    I pulled the logged piece of cat material out of the stinnger and it lookes like it had squeezed up as it was pushed down the stinger by the exhaust pressure and possible vibration from the motor. (stinger is funnel shaped.) So all that to say the honeycomb pores were really small.

    I always like the pics in the forum, so i have a few to show

    Question for the forum.

    Can a semi blocked exhaust overheat the engine?
    Did I screw up not noticing the cat blocking off the stinger, or is it something else.

    ps ordered a d plate today. Just nervous thinking I didnít fix the real problem melting my pistons.


    Thanks in advance.
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    Last edited by Voodoo121; 08-04-2008 at 09:59 PM.


  2. #2
    Duke's Avatar
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    Highly possible. If it created enough backpressure it could have easily overheated the motor to cause that.

  3. #3
    Goliath's Avatar
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    How would a CAT get clogged?

    Sorry I'm semi-new to PWC's and I just want to learn.

  4. #4

    Backpressure and detonation

    Hey all
    Just found this in post by Pho2Craft. Article was on detonation which seems to support the theory that too much back pressure will keep the flam in the engine and overheat a piston.

    I played with the CAT material a bit yesterday. I don know about being squished. The stuff looks like cardboard, but is hard as hell. What i am guessing is that the dia left is quite smaller than it is supposed to be. Its only slightly bigger in dia than the piston. Not sure if anybody knows what the original size (dia) is supposed to be.
    The CATs a bit oily though from the mixed gas i was running.


    As well i have a lump of somthing in the exhaust can that i cant shake out. any suggestions?

    Chow for now




    "(11) Avoiding excessive backpressure. Exhaust pipes always create back pressure, but the more there is, the higher the fraction of hot exhaust gas that will be unable to leave the cylinder during exhaust. Its heat, added to the fresh charge that next enters the cylinder, may push the engine over the line into detonation. Sometimes a one or two millimeter reduction in tailpipe ID will get you a couple of extra horsepower, but it may also push enough extra heat into the charge to make the engine detonate after a few seconds."

  5. #5
    TRIPLE PIPES ARE 2-STROKE TURBOS allcool's Avatar
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    Quote Originally Posted by Voodoo121 View Post
    Every now and then though if I held 4000rpm, the exhaust buzzer would go off. Stop ski, let cool go again. This went on for 1/2 the tank. Also every now and then the ski would just die (like pulling the chicken strap) at 4000rpm. Just wondering why would you disregard numerous buzzer warnings,,,
    for 1/2 tank no less ???
    ...continually stopping to let it cool will not ever fix anything.
    By the way, most of the time when a carbed 2-stroke dies at throttle it is a seizure.

    Can a semi blocked exhaust overheat the engine?
    Did I screw up not noticing the cat blocking off the stinger, or is it something else. Most diffidently will.
    Yup

    Just nervous thinking I didn’t fix the real problem melting my pistons. You got it right this time... might want to rejet to GH specs. IMO, since its apart again, this is a good time to check carbs& rejet.


    Thanks in advance.
    You figured it out this time around. Take some time and check over everything. If it doesn't run right don't keep on riding, stop and figure out what is wrong.
    jmho
    allcool

  6. #6
    Yea, good point. After the first time it stoped, as soon as i pulled the chicken strap and put it back in, the overtemp went away and the motor started right up. I was thinking i had a computer problem. I was thinking pulling the strap and putting it back in electrically re-set something. Should have looked harder i know. Still pretty surprised with all the mixed oil running through it that got that hot.

    still waiting for the D plate to get here. Weather here is prime for being on the water.

    Voodoo

  7. #7

    Lightbulb Update - carbs came off

    As I had the time I pulled the carbs off today and cleaned them. They were surprisingly dirtier than I expected. The major find was in the internal gas filters. Carb #1 and #3 were approx 40~50% clogged with what looks like old gas varnish. Brown cakey stuff. Interesting as #1 and #3 cylinder are the ones that burnt. So perhaps clogged CAT (BTW I found a large chunk of CAT material in my resonator pipe. Finally got it out) and slight restrictions on the fuel were the culprits.

    D-plate arrived, so today I am putting in the D plate and resistor and hopefully be able to give it a go .


    Clumps, mtf

  8. #8

    Angry Runs fine - whats the pinging?

    Well its all-together, started right up, however when it idles it pings with a corresponding shudder of the engine, every now and then. Understand i am a bit gun shy here now but it sounds like detonation? Can the timing be a little advanced? This is all in my yard with the hose on for cooling. I gave it a few small burps of throttle and it responded instantly.
    However the pinging has me concerned.

    Any ideas?

    Timing?

    Voodoo

  9. #9
    800AMSOIL4U's Avatar
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    Quote Originally Posted by Voodoo121 View Post
    Well its all-together, started right up, however when it idles it pings with a corresponding shudder of the engine, every now and then. Understand i am a bit gun shy here now but it sounds like detonation? Can the timing be a little advanced? This is all in my yard with the hose on for cooling. I gave it a few small burps of throttle and it responded instantly.
    However the pinging has me concerned.

    Any ideas?

    Timing?

    Voodoo
    Did you start it first then turn on the water?

  10. #10
    Thanks for the reply,

    Yup, was about 15 sec after it started before i turned the water on.
    I am not sure whay i do that though other than reading the cautions on the web. Could water potentialy flow into the exhaust port?

    Looking every where, cant find a note on how/if the timing is adjusted.

    Voodoo

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