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My boat Merc Cruiser V8 4brl, Thunderbolt IV 1978. Won't run well or idle, it back fires stutters and dies. This happens after it worms up. I rebuilt carb, cleaned out the old fuel, new fuel tank, Runs fine for a few min and then goes crazy.

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You need to replace your coil it is only about 15.00 it doe not sound like a fuel problem if the coil doesnt work you need to look at your cdi if you have the outdated box it will be mounted on the distributor it about a 1/4 inch thick 3 inches long and 2 inches wide with one flat plug going in it. before you do that change your plugsand wires wait im sorry i just saw the year of the boat now were getting somewhere you have a bad codenser if your boat has points under the distributor cap the condeser is the little siver cylinder while your in there you should just get a kit cap,rotor, button,points and condesor the points should be set at 25 to35 thousands i asume that 1978 is theyear modle if not like i said the new cdi box is out of date and very expensive $498.00 to be excact i would do a good tune up before turning to that but if it is a 1978 the distributor tune will fix your problem kit is about 70.00

Posted on Jun 28, 2009


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