mercury 500 thunderbolt lumpy when on half throttle

[chestercheese]

hello people
i have an mer 500, 4cylinder 1974 GETS LUMPY AT HALF WIDE OPEN IS THAT SOMETHING TO DO WITH TIMING AND CARB SETUP IT STARTS AND IDLES GREAT, ANY HELP WOULD BE GREAT,
MANY THANKS DAN

 

[Case450]

Re: mercury 500 thunderbolt lumpy when on half throttle

mine is doing the same thing...however i have an 86 25hp tiller...i changed the coils, plugs, wires, filter and put in fresh gas and some sta-bil...i can get it past half throttle now but it's kind of iffy...i'm currently searching these boards for something for mine...one guy mentioned that a "high speed jet" in my carb might clogged..something for you to check on yours?????? good luck chum!