How can you tell which bore?

[bign1514]

I've got a new superjet, and try to figure out if its been bored out or not. How can you tell if its been bored? Also, can you tell if its a 701, or 760? Also, can you tell what stroke it is 3mm or 4mm? thanks! any help would be greatly appreciated!

 

[sjetrider]

81mm is stock 701 bore / 84mm is stock 760 bore, as for the stroke you would have to do some measuring of the crank rods unless there is a visible plate under the cylender or unless its an aftermarket cylender. We need to know what you know before we can help.

Help ME help U.

 

[extreemthrottle]

what year ski is it? also does the motor have twin carbs or single carb. what color is the motor? got a pic of it? that would help. 701 and 650 motor (61x) will have the intake manifold where it turns and comes up is actually part of the motor. the 62t motor 701 and 760 both are typically black in color and the reed assembly is straight into the bottom half of the engine cases.
bore on a 701 i believe is 81.00 mm and 760 is 84.00 mm

 

[bign1514]

i bought a modded superjet built to race. As i can see and know, it pretty much has everything. It has a protec intake manifold. My compressions is around 150 psi on both, and its suppost to be around 175 psi with the protec head. If the cycl. been bored out, to my understanding it will lower compression. trying to figure out what they are bored out to.. thanks!

 

[yamanube]

If it is bored out, there is usually a number stamped/cast into the top of the piston that will correspond with the overbore size.

 

[Waste Land]

i bought a modded superjet built to race. As i can see and know, it pretty much has everything. It has a protec intake manifold. My compressions is around 150 psi on both, and its suppost to be around 175 psi with the protec head. If the cycl. been bored out, to my understanding it will lower compression. trying to figure out what they are bored out to.. thanks!

Boring a cylinder over shouldnt drop it that much. Porting however has a large play in compression

 

[keefer]

Increasing the bore size will raise the compression if you do not compensate with bigger domes. You need to check the domes after the bore is increased by 2mm from what I understand. Domes will vary depending on brand & style. At some point you will have to get the domes recut for the increased circumference of the piston and the squish relief will have to be recut also. For example I am running 82.5mm in my wife's 701 and I am using 84mm 38cc domes. I get 185 psi from this setup with her porting.