300/440/550 how to tell 440/550

[vomitspot]

one of my tard friends bought me a ( 440 he says ) to get running for him
its piston port i know that
badge on front of motor says 539 i think but that just bolts on
im a yamaha guy and know little about 440/550 other than im to big to ride one
this one has fpp 1/2 pipe and single sbn 44
im sure he built this ski by just bolting up a bunch of stuff he bought or collected
once i figure out what it is i will need a starting point on jetting
thanks in advance
jason

 

[Kohldanielzimmer]

If I recall 440= 68mm bore 550= 75 mm bore

Jetting for a single sbn with pipe. Start at 120 high 100 low 2.0 n/s and 80gram spring. One turn low adjuster 1.25 high