Merc 500 - 1965 50hp, Won't Stay Running Under Power

[Dunker]

I have just gotten a 1965 Merc 500 and at first could not get it running. I rebuilt the carbs, put in a new battery (which burned out the old starter) and replaced the starter. <br /><br />The problem that I am having, is that when I put it into gear (forward or reverse) it will bog down and kill. I have been able to barely get around this problem by opening the needle valve a bit more on each carb, but that still only allows me to run at about 30% power even under full throttle. (throttle stop is not the issue)<br /> <br />This problem does not happen in the driveway, only when the motor is under load. I have heard possibly fuel pump or points. The compression is good in all 4, and all of the plugs have also been replaced. Any help that could point me in the right direction would be a great help. <br /><br />I know I could just bring it to the shop, but when I bought a 1957 boat with a 1965 motor on it I knew I was buying a hobby, and I don't really want that hobby to be bringing it to the shop each year... Thanks in advance for any help.

 

[Chinewalker]

Re: Merc 500 - 1965 50hp, Won't Stay Running Under Power

Hi Chris,<br /> Have you got good, hot spark in all four cylinders? Spark in the open air means nothing - you have to have spark under compression. You can use a timing light to see if it's firing. You may have to simply pull the magneto, clean up the points, rotor and cap, and you might be good to go. Gap the points at .008". With the mag still apart, you can bench test it by grounding the mag body against a bench vice, and then holding the copper coil tang about 1/2" from the vice and then spinning the splined rotor clockwise. The spark should jump the gap... Reassemble the magneto and install spark plugs (Champion J6Cs) in the boots. Then with the plugs lined up in the vice, and the mag body grounded to the vice, spin it over - you should get spark in all four plugs. That little test saves you reassembling it onto the motor and discovering a problem and having the pull it off again...<br />- Scott<br />- Scott