RUCKUS AND METROPOLITAN CV CARB JETTING BASICS
Altitude - your Ruckus / Metropolitan is basically jetted for sea level.
If you are at high altitude you may need to lean out your main jet and/or adjust the idle mixture screw. Don't overlook the effect of altitude on jetting.
Humidity - your Ruckus / Metropolitan is basically jetted for nice weather.
If you are operating your scoot in a humid climate you will need to lean the mixture. This is also true near large bodies of water. Example: The Great Lakes or an inland bay.
Rider weight - your Ruckus / Metropolitan is jetted for the average weight rider (170lbs).
If you weigh less you may be able to get away with richer jetting. If you are heavy leaner jetting may be in order. In rare instances 230lb.+ riders may use richer jetting.
Main jet - your Ruckus / Metropolitan comes with either a 72 or 75 main jet.
Changes to the intake and exhaust will require some sort of minor increase in main jet size. Keep in mind the factors listed above will impact your main jet size.
With the stock carb and engine internals the largest main jet you should think about running would be an 80. I've seen up to 90 but later in the article we will explain this.
Pilot jet - your Ruckus / Metropolitan comes with a 35 pilot jet.
Changes to the intake will require some sort of minor increase in pilot jet size. Keep in mind the factors listed above will impact your pilot jet size.
The pilot circuit is very important for the CV carb. When changes are made to the intake you change the way air enters the carb, this has a huge effect on the requirements for the pilot jet. A much larger jet will be required to maintain fuel into the engine. The engine is running on pilot circuit to about 20mph in the case of the Ruckus / Metropolitan. Any problems with acceleration up to 20mph are pilot jet problems.
A common mistake is to run too rich a main. Ignoring the pilot jet is the cause of this. A rich main will help cover a lean pilot but will also reduce your top speed. If you are reading this for a Ruckus / Metropolitan you don't have extra speed to spare. Don't cap your top speed with some ridiculously rich main jet.
Rev Limiter - Often overlooked, the rev limiter can effect jetting.
Don't jet around or to compensate for the rev limit. Keep in mind the rev limit should be avoided by changing the drive unit tuning or the limit itself. A common mistake is to run extra lean or rich jetting because the engine is hitting the rev limit with the proper jetting. If you are tuning without a tach you are wasting your time.
Choke - Keep in mind your choke may be on.
When tuning keep in mind the auto choke enrichment is on at some degree for about 10 minutes. Your engine should start but it will never run good with the choke on. Don't make the mistake of jetting during the ever changing period while the auto choke is running it's enrichment cycle.
Fuel - Run quality fuel.
You don't have to run high octane but just run good fuel. Keep in mind fuel across the country is different. The same goes for fuel in other countries. The fuel in other countries is often blended to work best for that climate. This is the reason we can't just say, "Hey, put a # in it". We'd be lairs. It would be easy but you would be slow and we can't have that.
READ THE CV CARB JETTING FOR MORE INFO ON JETTING A CV CARB