Home Forums Shifter Karts Building a Stock Moto CR125 Reply To: Building a Stock Moto CR125

Patrick Roth

Now that I have the disclaimer out of the way, I’ll see if I can’t be more helpful… ;) I’m unable to view the ebay item so I’ll make some assumptions.

1) A key decision is to go with either a 99 or a 01 top end.  Based on price alone, the 99 is cheaper and there is arguably little, if any, performance gain by going the 01 route (but the 01 is the choice of just about every SKUSA racer out there).  I’m going to assume you’ll be going with a 99 top end.

2) A complete rebuild kit (both the top and bottom, less the crank) can be had for about $500 from Fastech.  You could also identify the parts and try to save a few bucks by going to a large distributor such as Partzilla.

3) If you go with a new crank make sure you get the slip fit available from a karting specific supplier.

4) For the top end you’ll need a 99 cylinder and head with a set of power valves installed.  The nice thing about the 99 is the power valves can easily be removed and installed on another cylinder.  Depending on how complete your bottom end/engine is you may or may not need some additional items (cylinder studs and nuts, water hose joint, etc).  DO NOT HONE THE CYLINDER (it has plating)!

5) Hopefully your motor will come with an intake boot and reed cage.  If so take a real close look at the reeds and replace if there is any sign of cracking or fraying.  The safe bet would be to replace the reeds to put you at ease.  If it doesn’t come with the intake boot and reed cage, you’ll need to buy them.

6) The “hot” carb is the Keihin PWM carb.

7) As long as your track allows, the cheap route is to go with an air filter intake rather than an airbox.  The air filter is the preferred route.  I recommend a support of the filter/airbox to keep the intake boot from ripping.

8) On the exhaust side you’ll need a flange coming off the cylinder.  In my opinion, they all stink so pick your poison.  The o’rings constantly need replacing or the OEM metal band also will crack and fall apart over time (I don’t like this one because it seems like an opportunity for small metal parts to get into the cylinder).  The 01 has a nice manifold with a wide rubber seal but this won’t work on the 99.

9) SKUSA runs a SK1 exhaust pipe; however, check your club rules to see if the RLV pipes are allowed.  If the RLV pipes are allowed you may want to put a wanted to buy ad on this site as there is likely a SKUSA racer that has a pipe laying around from before the switch to the SK1.

10) For a 99, a 14″ silencer is what I ran and is what I’ve seen many other people run.

11)  Mounting brackets – I highly recommend the MRC brackets for the coil and CDI as it moves everything to the back of the seat and takes away the vibration which seems to be the cause of several failures.  MRC also makes/sells nice exhaust pipe and silencer brackets at good prices.

12)  I recommend going with the MRC fuel pump and mounting bracket.  This is a single pump and simplifies everything.  I haven’t had a single issue with this setup.

13)  Electronics – I hope you got the CDI and coil with your bottom end; otherwise, you’ll need these items ($$$).  I’m assuming the stator is coming with the motor (if not this is another big $$$ item).

14)  Cooling – Closely inspect your water pump impeller and bearing (not sure if this is included in a bottom end kit) when you have the bottom end in pieces.  Replace if needed.  As far as the radiator goes there are a lot of options.  I recommend calling RPM Racekarts as they sell low cost radiators with a nice mounting bracket.  I’m sure there are others out there, this is just what I have found.

Hopefully this helps!  If the $$$ adds up to more than you are willing and decided to go the used kart motor route, I just notice a DDR 01 package go up for sale for $4k from Roy Montgomery.  Included in the package are two cylinders so you could buy the package and sell the other cylinder.  I know Roy and he is meticulous about his stuff and since he is a karter his package should fit the bill.