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  1. #1

    catalytic converter and jetting

    Is it necessary to change the needles and seats or make other jetting changes if the CAT is removed and you want to run at wide open throttle?
    I just bought a 2000 Yamaha 1200 xlt. All original factory except the catalytic converter was removed and some kind of computer chip/plug installed in the wire connector that would have gone to a sensor on the exhaust pipe. Previous owner said he loaned it to a friend who said it stopped running while in the middle of the lake and has not run since. I assumed he just ran it out of injection oil.

    I took it apart and found the middle piston was heavily scoured and rings jammed and only had 40 lbs compression. Engine would sieze after a few minutes of hard running on the lake. Would barely crank (new battery) after a few minutes of cooling. So I just put in a new piston and new carb kit that came with three mixture screws and I noticed no mixture adjustment screws in the carbs themselves???

    While searching this topic I see that the siezure may be from lack of fuel at high rpm??? I was just going to switch to premix fuel and oil and run it again, but now I'm not sure it won't sieze again. It also appears that the front and rear carbs can get extra fuel from some kind of fuel regulator mounted to the rear carb (what the heck is that?). Yes, I do have a factory service manual on order .

    I'm considering just putting the original cat converter back on. I don't care about speed. Do these carbs have mixture screws that are plugged over and if so, can and how do I remove the plugs?

  2. #2
    Crash Test Dummy Smitty's Avatar
    Join Date
    Jun 2006
    Cullman, AL
    First, welcome to the forum!

    OK, might not be able to tell now what caused the seizure. You should have replaced the cylinder if it had any marks on it. You should pull it back apart, pull the cylinder, and check it out.

    The chip is a temp sensor chip; the cat converter has been replaced with a "d-plate". Keep it, it's not the cause of the seizure.

    The carbs have caps over the high and low speed screws. You will have to remove the caps to get to them. Don't worry about that yet, when it's time we have pleny of info here about rejetting carbs.

    Your first job is to figure out why it seized and find out what is damaged. Check compression and pull the head again, then get in there and look at the cylinder walls. You said you thought he ran it out of oil; was the oil tank empty?

    Stick around.... let us know what you find and everyone here will get you running right. Here is a link about the XLT's.

  3. #3
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas
    Welcome to the forum

  4. #4
    Water Bum Rodneyae's Avatar
    Join Date
    Dec 2006
    Roanoke, Va
    Welcome!!! Everyone here is great and very helpfull!!!

  5. #5
    Caution raider fan in the area !!
    Join Date
    Jul 2006
    Sacramento, California, United States


    welcom jetskiron

  6. #6


    thanks for the great welcome, but just got smacked.

    I just entered a lenghty reply and got a message that I was not logged in or something, but I was. I hit the back button and all my text was gone. Guess I should have done a "controll c" before posting????

  7. #7


    Ok, here’s some more info. and pictures (I may have to upload more pics with a followup reply since it appears I can only upload 4 pictures?).

    • The oil lines had no leaks. However I have not tested the oil pump. Unless someone has a better idea, I thought I would take the pump off and spin it with an electric drill to see if it pumps?

    • The pic of the piston is the center piston. The rings were jammed and the sides of the piston scoured. It only had 40 lbs of compression (the front and back pistons had 110 and 115 lbs).

    • The front (mag) and back (pto) piston had some burn marks and light scouring on the sides facing the exhaust and intake ports.

    • The center cylinder has a small gouge about 3/8 inch vertical and about 1/8 inch wide and 1/16 inch deep and located about ˝ inch above an intake port.

    • All three carburetors had a section of rust color mineral deposits on the bottom of the regulator body (water not cleared out?) and around the screw for the regulator body valve underneath.

    • The front and center carb pump body small clear check valves had kinks.

    • Pop off pressure – on all three I went to 65 lbs and stopped there. I was not sure if I was damaging the pump diaphragms with the high pressure?

    • Jetting – n&s on all three is 1.2 with a gold spring, main jets are 117.5 and pilot jets are 87.5. The same on all three.

    • Power valve clearance from top of shaft to cap base was 13mm on the front and 14mm on the center and rear valves. There was a little slop in the connections between the valves, about 10 degree difference between the front and back. There was no shiny metal on the ends of the valves by the pistons. They were between 1 and 3 mm away from contacting the pistons. No Wave Eater clips installed.

    • MOST INTERESTING is what appears to be a factory defect? Both nipples where the accelerator pump lines go into the front and rear carb throats were blocked off inside. The large port in both elbows was blocked just before the turn into the small port. After removing the elbows, I discovered that the nipple, which reaches inside the carb throat, was blocked at the tip on both carbs. So my question, if this was intentional by the factory, why bother installing the accelerator pump? (There was no elbow or nipple on the center carb).

    • The ski has a Riva free flow exhaust kit, stock air cleaner and D plate and chip. No return fuel line restrictor was installed. All else stock except intake grate.

    Ok, so I’ve replaced the center piston and rings and installed new carb kit with n&s on all three carbs. Now my big questions:

    1. Do I need to change the jetting?

    2. Should I remove the fuel mixture caps and adjust the mixture screws?

    Thanks much.
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  8. #8


    heres the rest of the pics
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  9. #9
    WATER WOODY's Avatar
    Join Date
    Aug 2005
    Minden, Nevada, United States
    How many hours on this ski? Looks like carb rebuild time.I would pressure test the motor after you get it back together to check for air leaks.Put a new fuel filter in also.Remove your fuel flapper door in the pickup.Install new fuel lines on the carbs while your there.I recommend going to premix also.Lets make sure the carbs are the cause of all this first.Be sure to check your reeds.There are lots of things to check.There are plenty of people here to help.
    Last edited by WATER WOODY; 02-24-2007 at 07:05 PM.

  10. #10
    WATER WOODY's Avatar
    Join Date
    Aug 2005
    Minden, Nevada, United States
    Your piston wash says its on the lean side.

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