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This is the mother of all upgrades,  a complete changing of the motor to pretty much any size/power motor your heart desires... Within reasonable limitations of course!  Because the MadAss uses the standard Honda horizontal mounting pattern, your options are extremely broad.  With several proven Chinese manufacturers, motors are readily available and, for the most part, fairly cheap.  We looked at the 2 largest manufacturers out there, Jailing and Lifan motors.  These are not by any means the extent of motors available.  Manufacturers like GPX, Zongshen, YX, and Loncin all offer other options for your motor upgrade.  Also let it be noted that the current OEM 50cc motor in the MadAss is actually a Jailing motor tailored for Sachs.

Be aware that there are a lot of options out there, and in those options lies a lot of Chinese garbage.  Be sure to choose a motor/manufacturer that has been proven for quality and reliability.  Keep in mind the old saying: You get what you pay for!  There are several motors on the market going very cheap, and that is exactly what you get in the end, something very cheap.  I would strongly advise not wasting your money on garbage.  It will only cause you hours of frustration and more money in the long run.

After numerous considerations, lots of reading and hands on experience feedback from our friends at we decided to try the new 2008 Lifan 150cc motor the new upgraded transmission with 4 up gears, large valves and 15mm wrist pin.  This newcomer has had a lot of buzz about it, and we decided it would be our best over all option for our MadAss while giving us the option to further upgrade performance in the future.

We are currently working with to provide an all-in-1 complete upgrade kit for the MadAss, hopefully to be available soon.  There were many complications involved with our motor swap, and we hope to get everything ironed out and made available to you for an easy drop in - plug in motor upgrade.
Fast Trails Performance now has several motor swap packages available.  Complete with everything you need to upgrade your MadAss to a rippin bike!  Available are a 125cc automatic for those who wanted a 125cc but were stuck with a 50cc instead.

They also have 140cc, 150cc and 160cc performance motors available.  All have the top mounting hole machined to fit the MadAss properly and the correct 3 phase stator installed so the motor simply plugs into the factory harness.  Kudos to FTP for making the 3 phase stator and putting these awesome packages together for the masses!  You can see all the upgrades available for your MadAss here!

1.  Let me first start with the fact that I am NOT a mechanic.  I have been working on motorcycles and scooters for a long time and know a little about what I am doing.  I simply take pictures for other people to use as a guideline to help them modify their own motors.  Any modifications you perform are done completely at your own risk and liability.

2.  Tampering with your motor in any way may void your warranty.  Make sure this is a sacrifice you are willing to make before you begin working on your own vehicle.

3.  Before you begin, read this ENTIRE article from start to finish so you know exactly what is involved and what steps are required to properly complete the procedure.  Also make sure you have a nice clean area to work in.

4.  This example was performed on a 2006 Sachs MadAss 50cc automatic.

5.  ALL bolts and socket head cap screws are in metric! Don't try to work on your vehicle if you don't have metric tools, you will just wind up messing up the heads.

Swapping the motor is actually a very simply task to perform.  All the Honda style horizontal motors are only held on with 2 bolts.  So removal and installation are very simple to perform.  The task is much easier however if you have 2 people to get the job done.

Let us begin!  You will first want to start by removing anything attached to the motor:
  1. Remove the fuel line going to the carberator.
  2. Disconnect your throttle cable by unscrewing the top of your carberator.
  3. Disconnect your choke cable
   4. Disconnect your exhaust: Remove bolt under seat, remove springs holding muffler on with a pair of pliers, remove 2 nuts holding exhaust onto the motor.

Once the bolts have been removed and the springs disconnected, simply slide the pipe towards the front of the bike and pull it out of the muffler.

   5.  Remove the chain: Remove the master link and pull the chain off. 

   6.  Disconnect the spark plug boot and remove the bolt holding the spark plug wire to the motor. 

   7. Disconnect wires going to and from the motor: Disconnect the starter wire from the starter relay, unhook the CDI Box, disconnect the rev limiter and remove it.  Unhook the white connector coming from the motor going into your rectifier.  Disconnect the blue and white wire coming from the motor.

   Note:  If you don't intend to install a motor with electric start, you can remove the starter relay entirely.  Also you can get rid of the rev limiter...  This is just a restriction on the factory motor and impedes your motors performance.

   8.  Remove the ground wires on the motor:  There are a total of 2 wires grounded to the motor, one on each side of the bike.  Use an 8mm socket to remove the bolts and take the ring terminal off.  Replace the bolts once the ring terminals have been removed.

For the following steps, you need to prop up your bike.  We are lucky enough to have a fork lift, but a saw horse or something equivalent will work.
   9.  Prop the bike up so it can't tip over.

   10.  Remove foot pegs and kick stand: 4 bolts on the bottom of the motor hold the entire assembly on.

  11. Remove the 2 bolts holding the motor in the frame:  Remove the lower one first.  Rotate the motor forward by pushing on the cylinder head in an upward direction.  This will give you a clear view of wiring connections.  Be sure that there is nothing still connected to the motor, then, while holding the motor and applying some upward force, push out the top bolt.  The motor will drop into your hands.

Once the motor is clear of the frame, set the motor aside as you will not be needing it any more!
New Motor Installation
Now is the time to bolt in your new power plant.  In our case we chose the Lifan 150cc.  Unfortunately the motor only comes in silver.  We couldn't bring ourselves to drop a silver motor into our MadAss and ruin the awesome flat black color scheme.  So we purchased a few cans of Flat Black Dupli-color High Temperature Ceramic paint. We were now ready to remedy our dilemma.  We started by washing the motor with a mild detergent to remove any oil from the paint.  Then we gave it a good wipe-down with rubbing alcohol.  Once we were confident that any oil residues and dirt were eradicated from the motors surface, we hung the motor from the ceiling of the garage.  The we meticulously taped off every chrome bolt head.  After an hour or 2 taping, we were ready to paint.  We applied 4 coats of paint in about 30 minute intervals.

Now there is a decision for you to make.  The top bolt on the original Madass motor is 10mm and the bottom bolt is 8mm.  Most horizontal motors don't differ in size and they mostly have 2 mounting holes for 8mm bolts.  So you will have to decide on 1 of 2 solutions.  The first which I would recommend to most.  Get a high grade 8mm bolt and replace the 10mm bolt with an 8mm bolt.  The second solution which is the route we went with, we drilled the hole out to clear the larger 10mm bolt.  If you are unfamiliar in working with this type of situation, don't do it.  You could wind up drilling your hole off to one side and ruin your motor mount.  Great care must be taken to ensure the hole is drilled out in the same path as the original hole.

Once you have decided which method of mounting you are going to use, lift the motor up into the frame and push the upper mounting bolt through the motor and out the other side.  Now rotate the motor forward and push your motors wiring through to the back and leave them hanging in the battery compartment.  Make sure the oil over flow tube is located properly - we ran ours out the side where the brake is, as running it straight back would not work because the second mounting hole would squish the tube.  Also be sure the spark plug wire is running on top of the motor.
Once you have the motor in and you are satisfied with it, push the second mounting bolt through.  Tighten the mounting bolts up and re-attach the foot pegs and kick stand.
Once you have the bike sitting on its own feet again, now you can begin by hooking up your carb and clutch.   Bolt your intake manifold onto the bike then attach your carb to the manifold.  Hook up your gas line and throttle cable.
The throttle cable can be re-used with the new carb.  Simply disassemble the top of the old carb and remove the cable from the slide by pushing the spring down and creating enough slack to get the end of the cable through the eyelet.  Push the cable into the top of the new carb, place the spring over the cable and attach the new slide by compressing the spring and push the cable through the eyelet and lock it into place.
Now you have to attach your clutch.  Start by attaching the clutch perch and lever.  Run the new clutch cable down to the motor and attach it to the motor.  Then attach the cable to the lever.  Adjust the slack out of the clutch so that there is little to no play in the clutch lever.  Use wire ties to pull your cables up nice and clean.
Attach the spark plug wire to the motor with the small wire clamp.  Then plug your spark plug in.
That is pretty much it for mounting and attaching the motor.  Now time for the wiring.   We ran into all sorts of complications with the wiring on this bike, so be sure to visit our Wiring Guide for electrical hook-up specifications and visit our Oil Cooler page for hooking up an oil cooler for your new power plant!

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