A stroker crank is designed to do one thing, make the motor displacement larger, which will
make more power.  A stock Go-Ped motor is 22.5cc.  With a 2mm stroker, the displacement will
increase to 24.1cc.  This may not seem like much, but it does make a difference. 
 
The stroke is determined by the distance from the center of the crank to the center of the
lower rod pin(where the rod connects to the crank).  On a stock crank this distance is 14mm. 
So, the distance the piston travels from the top of the cylinder to the bottom is twice that,
28mm.  Therefore a 2mm stroker would be 30mm total stroke.  Rod length has nothing to do with
the stroke of the crankshaft.  Longer rods, however, can reduce piston skirt pressure on the cylinders walls,
 if the stroke to rod length ratio is not within reason. 
A 1mm stroker is not really worth the money or the time.  The only reason people use 1mm
stroker is because it will alter the port timing less and can be just bolted in.  
When a 2mm is not setup properly a 1mm will out-perform it. 
First of all, you cannot use an 1148 cylinder with a 2mm on the old style straight plug
motors.  The transfer port timing is way too high for this.  High transfer port timing will cause a loss of bottom end power.  Use the stock 1140 cylinder, and do not alter the transfer
or intake port heights.  If you are looking for hard acceleration, don't even port the exhaust. If you want more top end, raise the exhaust a little (no more than 170 degrees duration).  Do
not use more than 1 base gasket.  All of the 1140 stroker I have built so far have required no head machining.  The 2mm will bolt in the stock 1140 cylinder,  Just make sure the piston to
head clearance is no less than .017".  This combination runs best on alcohol.  To run race gas you should use a billet head kit and don't use too thick of a head gasket.  Keep the squish
between .017-.025".  Get either a race gas head or alcohol head, one head does not fit all.  Do not fix compression by changing gaskets.  Squish clearance is critical on these motors.  Too
wide of a clearance will cause noticeable power loss.  If you are using the new style G23 slant plug motor, then there is more work.  The cylinder
head must be machined 'up' to give the proper squish clearance.  Again, do not stack base gaskets.  If someone tells you to do this, they don't have a clue.  The squish clearance should
be between .017-.025".  If you want to run race gas, the head must also be custom cut to increase the head volume.  Just machining the squish will give proper piston to head clearance,
but the compression is too high for gas.  It will run best on alcohol.  As far as porting goes, do not raise the transfers.  Raise the exhaust port about half-way up the notch and widen.
Widen the intake, do not alter the height.  A properly built stroker motor will out perform a stock stroke motor in every aspect.  
You just have to take the time to do it right or be willing to spend the money to have it done right. 
 
Note:  We are currently working on a billet cylinder for the G23 slant plug motor.  It will come as an assembly with 2mm stroker, cases, billet cylinder, and a billet head with removable
domes.  Domes will be available for all fuel types.  This engine will be built for maximum power, with nothing else comparable.