Tuning and Modifications: Learn how to De-Restrict your scooter for increased speed and acceleration


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 guide line 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, make sure you have a nice clean area to work in.  A small amount of dirt can be a big problem when working on the innards of your motor.  Keep your hands, motor, and any other parts you are handling very clean.

4.  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 end up messing up the heads.

Background Information
Almost all scooters have one or more of the same restrictions described here.  There are three restrictions covered here:
  1. A variator restriction
  2. An exhaust restriction
  3. A jet restriction in the carburetor

The Mojito has FOUR restrictions on it. they include: a jet restriction in the carb, a washer in the variator, and 2 on the exhaust. I will make several postings to show all the steps you need to complete the de-restrictions.

The sr-50 ditech only has 2 restrictions on it, they include: a washer in the variator, and you have to have a dealer re-map your injection system...  The exhaust doesn't have any restrictions on it, but you really need to get a high performance exhaust to get good performance.


Removing the variator restriction

First start by removing the socket head cap screws to remove cover on the left side of the scooter... Be careful of the gasket, my Mojito had a gasket, but my DiTech didn't. Ignore the remove kick start in photo... I am used to working on motorcycles, and the kick start is actually attached to the crank and you have to remove it to get the cover off. But on these scooters, you DO NOT have to remove the kick start.
This is what you should have removed...
OK, now you should be looking at the whole drive train... The variator is on the left, and the clutch is on the right. To remove the variator, you need an impact wrench... You will simply turn the motor with a wrench, IT MUST BE IMPACTED OFF!!! If you need to take the clutch off, simply hold the back brake on while removing the bolt.
Once you have the variator off, you will notice a washer located between the two halves of the pulley... THIS IS A RESTRICTION!!! That little washer does not let the two halves come completely together... Removing it makes a big difference in top end.
After the washer has been removed, re-assemble the variator onto the crank shaft. Make sure the Starter gear behind the variator is on the spline, and make sure the variator is all the way pushed to the back before tightening the bolt. The bolt must be impacted on, and be sure to use some loctite on the bolt before tightening the nut. It will have a tendency to spin off, so LOCTITE IT!!!

Removing The Main Jet Restriction In The Carburetor

I am not sure what the stock jet size is, but it is small. Get yourself a larger main jet. I went with the .8mm jet, with shipping it was like ten bucks. Ask around in forums to see what the best jet size is for your scooter and your set up.
The first step is removing the carb. You have to disconnect all the cables and hoses. Be careful when doing this, work in a clean environment. A little bit of dirt in the carb is a bad thing! Keep needles from the choke and throttle from touching anything. When the gas line is removed, stick a screw in it to keep gas from leaking.
This is how you take off the choke!
Once everything has been disconnected, remove these screws to take off carb.
The carb is going to be filled with gas, so be careful! Lay a paper towel down and flip the carb over. Remove the two screws on the bottom and take off the bottom cover.
Use a clean flat head screw driver to remove the jet. Simply screw in the new larger jet in its place and re-assemble carb. Bolt the carb back on and re-attach all the cables and hoses. When putting the throttle cable back in there is a channel and a key that has to line up. Turn it until it lines up and falls in all the way.

De-Restricting Your Exhaust

Most stock exhausts have some sort of restriction on it.  But at the same time, not all do.  The example shown here has 2 restrictions on it.  Now your exhaust may not be exactly the same, but this should give you a good idea of what to look for.  Some exhausts have a restrictor washer right at the exhaust port where the exhaust bolts to the cylinder.  If you remove your exhaust and see anything that might restrict the flow of your exhaust, chances are it is a restrictor.  Ask on a forum to see which restrictions might be present on your scooters exhaust.

In most cases, de-restricting your exhaust is a pain in the butt.  Purchasing a performance exhaust is usually an easier and a better way to go.  Performance exhaust will usually out perform a de-restricted stock pipe.  But if you are on a low budget, this is the way you will want to go.

First remove the exhaust from the scooter.  Look for any washers or flanges that might be restricting the flow of air.

On this pipe, you will notice a flange and a little pipe coming off to the side that just stops. These are where the 2 restrictions are.  You have to grind the bolt heads off to get to the flange, and you have to cut off the little pipe coming off the side.
Once you have ground off the bolt heads, you will be able to see the restrictor. You will notice a large pipe coming through the flange, but there is a smaller pipe welded inside it. You now have to cut off the small pipe behind the weld. Use a file to smooth out the burrs. Make sure you clean out all the chips before re-assembling.
OK, now that little pipe that had to be cut off... The proper way to do this is to cut it off and re-weld it shut. But if you are like me and welder less, I just left enough pipe to crimp and fold it over. I put the end I cut off into my vise and closed it until the pipe came together. After that I took a pair of vise grips and bent the fold in half. Then I beat it with a hammer until it was completely closed. After that I took a grinder and smoothed it over. I guess some JB weld or some exhaust tape might work also.
Now you need to re-assemble the exhaust. You are going to need some new bolts to replace the ones you cut off. I was able to buy the same thread bolts and put them through the nuts that were left welded to the other side of the flange. But if the nuts are messed up on the bolts from the weld, then you will need to grind the nuts off and use new nuts and bolts. Use some high temp black paint to paint over all those unsightly grinding marks you made! But it should look like this when you are done!
OK, all you have to do now is re-attach the exhaust to your scooter. Be sure to get the gasket between the pipe and the head back in its place.

And that is it for de-restricting! on the Mojito, the washer and jet did absolutely nothing to the performance alone. But once the exhaust was done, it made a world of difference.

As I said before, it is a pain in the butt to de-restrict the exhaust, just shell out a couple of bones and buy a high performance for it instead!

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