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Thread: 1999 HP500 Mercruiser Carb Motor

  1. #1
    My Hp500 started up this season with no problems. The motor has 132hours on it since new. After 1/10 of an our it started running rough and missing, it stalled a few times. I got it back to the dock and on the trailer. I pulled the plugs and they were carbon filled. I changed them out and put in ne AC DELCO Mr43T plugs. The boat ran great for the rest of the day. The boat sat a week. I started the boat and it ran a little rough, skipped a few times. Then was ok, ran it for another 15 minutes or so and decided to pull a plug. The plugs were all the same as before, dry carbon, solid black. I am not a super motor head, the plugs are the correct ones, the wires are new, cap and rotor are also. Could the choke be causing this, or is the carb out of adjustment?? Any help would be greatly apreciated. I know the motors are better running a little rich but I should fol plugs after 15 minutes.

  2. #2
    Check to see if the choke is open all the way when warm. If not, the choke heater is likely burned out. It is the round looking cap with 2 wires going to it. Make sure you have power and ground when engine is running. Then disconnect the ground at the heater, and put a test light between the ground wire and terminal. If it doesn't light, heater is open(bad).

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