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  1. #1

    STX DI Running Poorly When Hot... Ideas?? Help!?!?

    My 2000 STX DI with 120 hours used to run great. I consistently got top end of 55 mph at ~6500 rpm out of her. Now, I'm only getting a top speed of 49-51 mph at 6200 rpm.

    I could live with the 51 mph if it would last. However, after about 5 minutes of riding, the rpms drop to 5800 and top speed drops down to 35-39 mph. If I stop and let her sit for 20 minutes or so, rpms are back up and speed is up to 51 mph again. I think this is definitely a heat related issue.

    There are no clogs in the cooling lines. Compression is equal at about 110 psi across all 3 cylinders. I recently rebuilt the jet pump, cleaned the injectors, replaced fuel filter, replaced the spark plugs (3rd set this season - she seems to foul them often), checked temp sensor, and checked throttle position sensor input and output voltage (at specs).

    I'm not getting any warning indicators or lights, and the engine seems to be running fine, just slower. The engine does not seem to "miss" or stumble when this is happening.

    I'm stumped. Does anyone have ANY ideas on what the problem might be?


  2. #2
    axgrider73's Avatar
    Join Date
    Feb 2007
    Southeast Ohio
    Lean condition? Have you done any WOT plug chops?

  3. #3
    If your EMM has never been repaired and upgraded you need to give these guys a call and get your EMM serviced before you spend any more money on other things. the price is like 700.00 for this service but if you plan on keeping this boat it's a must. 866-298-1510 Direct Fuel Injection Technoligies Inc.

  4. #4
    Quote Originally Posted by axgrider73 View Post
    Lean condition? Have you done any WOT plug chops?
    I appreciate the response, but what is a "WOT plug chop"?


  5. #5
    btldigger's Avatar
    Join Date
    Feb 2007
    lebanon tn.
    A plug chop is when you run the ski for a minute or so at wide open throttle the hit the kill switch. Pull the plugs and check the color. If you let it idle it will throw the reading off.

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