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Mercruiser help

Discussion in 'Boats and Motors' started by Bapenn, Apr 16, 2004.

  1. I have a 120hp inline 4cyl Mercruiser sterndrive. My problem is a idle problem. I had the complete outdrive rebuilt a year and a half ago. Rebuilt the carb last spring. Replaced the fuel filter last spring. I have the idle great out of gear. Runs good wide open but the thing won't idle when you put it in gear. I am thinking maybe the fuel pump needs rebuilt or another fuel filter. Just wandering if anyone has had that problem or have any suggestions that I might have missed.

    PS. I almost forgot. 1977 Mercruiser 120hp 4cyl. I also put new plugs wires, cap, rotor, points and condenser. Thanks in advance.
  2. Mercruisers have a switch that kills power to the ignition momentarily as you are shifting gears. I believe it's called a shift interupt switch. On my old Mercruiser it was on the assembly on the transom where the throttle and shift cable from the front transfered to the shift and throttle at the rear. An easy way you could check it would be with a 12 volt test light. With your engine running in neutral, your test light should be lit when checking the positive side of the ignition coil. When you shift into gear, it should just blink, it it stays out, it's killing power to the engine and that's why it's stalling. Now if you can run a small jumper wire from the battery positive to the coil, bypassing the switch, and your engine keeps running, you can be sure it's the switch that's the culprit. It's more than likely just an adjustment on it or spraying it with WD-40.

  3. Do you have any more info, like does it just die, or stumble .... speed up, then die or slowly idle slower until it dies. The more info you give the better the chance that someone can help ...Is it possible its overheating .. do you have a temp gauge..