Originally Posted by melscharf
The 440 to 550 upgrade is an easy swap, you will need a yamaha 650 carb cause the stock 550 carbs are garbage and you will need to make a spacer plate about 3/8" thick I make them out of a piece of plastic or aluminum between the intake manifold and the jugs. Also you should be sure to install a stainless prop in the 440 pump I would not change the pump the 440 is actually better.
+1 to that. I was able to use the 440 carb on my 550 engine when I did the swap. I had to tweak the mixture settings a little but I've had 0 issues with since.
-1984 JS550 clone -
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, 440 pump, Skat Trak, primer, thumb throttle
-1987 JS550 - bone stock
-1985 JS550 basket case