losing rear piston- crank torsion?

[derek]

i was just reading up on this subject. 650x i just bought rear piston wasted. then i looked at my 720 out of gti i just tore down. not as bad, but showing signs of burning piston. this was in a ski that was just driven around, not hammered. crank torsion. retarding rear piston under heavy load at high rpm effectively advancing timing on rear cyl. some people are even building in rear cyl retard at higher rpm's. here is a thought; why not build the crank with a couple of degrees of advance to the rear cyl? then, under load it is straight up instead of late? at light loads the slight power loss because it is retarded won't be missed as much, i would think.

 

[robin savell lloyd]

What I have read is to make sure rear cylinder carb is jeted richer than front cylinder. That is what alot of pwc racers do. I believe that some come stock this way but I can allways be wrong.

 

[derek]

there are a lot of things people do to compensate. richer jetting. lower compression. retard timing. why not just advance the rear cyl so that it twists back into correct timing at full load and is a little timing-retarded at partial loads?

 

[robin savell lloyd]

They do sell high performance ignition systems that are adjustable I do not know if they will allow for seprate cylinder timing curv but they might. :agree: