79 Merc 500 50hp No Power

lkiester

Recruit
Joined
Mar 23, 2009
Messages
1
Ive got a 79 merc 500 50hp that max speed is 6 mph. It used to run awesome 30+mph. Then last year i was out on the lake all day fishing and the motor just basically died on the way to the boat ramp. As i managed to get it there. Cleaned the carbs, new gas, new plugs, new fuel filter, bulb is staying primed. ran good for about 5 min on the lake the next time then did it again. THen i had a mechanic rebuild the carbs. ran good in the tank. runs great as long as its not under a load. wont go over 6 mph. took it back to the mechanic, they wanna charge me again to fix it so i decided to try here first see if anyone can help.
Thanks

Luke
 

bullbat

Petty Officer 2nd Class
Joined
Mar 10, 2009
Messages
152
Re: 79 Merc 500 50hp No Power

you need to make sure that you are not losing spark, use should get an inline spark tester and make sure that you are still gettin good spark when under a load, and also make sure that your timing is advancing
 

rabeck5792

Petty Officer 3rd Class
Joined
Mar 2, 2008
Messages
75
Re: 79 Merc 500 50hp No Power

i had one that was idled allot,found the exhaust tube totally plugged with carbon.you need to make sure linkages are working correctly, & you dont have an ignition problem like a bad charge coil in the stator.
 
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