Category:Performance Tuning

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Required Reading

To familiarize yourself with two stroke engine tuning, read the "Two stroke tuner's handbook" by Gordon Jennings.

Better, Faster, Stronger

You'll get noticeable power improvement on most mopeds by the following performance mods, however, the system is tuned to work together overall, so changing one variable may affect other components, and require further tuning. The most common example is the need to upjet when changing any part to one that allows the engine to consume more oxygen, such as a bigger exhaust, carb, cylinder kit, etc.

Bigger Carburetor

Installing a bigger carburetor will increase the amount of fuel leading to more power. The hard part is getting the air to gas ratio correct so that you don't cause a seizure or foul plugs. Controlling the gas flow can be done by changing the size of the jet. Controlling the air flow can be through the use of special air filters or by drilling holes in your air box.

You can also try over-boring your carburetor. The process isn't very hard and saves a lot of money.

Click here for more info Over Boring Carburetors 101

Performance Exhaust

For most mopeds, this will be the best performance improvement, and the easiest for the average person to do in an afternoon.

Many mopeds of 1970-1985 vintage had exhausts tuned to deliver the most power at approx 25mph. As the engine goes faster, it's cycle rate moves out of the power band of the exhaust, and the exhaust begins to restrict the amount of fuel available for combustion, which self-limits the top speed.

However, if you replace the stock muffler with one with a power band that is higher, your top-end speed will increase, but at a cost of the low end power. For most moped riders under 200lbs, this really isn't an issue.

For example, on a Honda Hobbit, you can get up to an 8mph improvement, just by swapping out the stock muffler with a Proma Circuit exhaust.

Of course, every model of bike is different, and you'll need to use the forum search function on the 'Performance Tuning' forum to find what people recommend for your model.

To learn more about how expansion chamber exhaust sytems work, read this great primer:

For a summary of Puch Maxi exhausts, you can look here: Puch Exhausts

High Flow Air Filter

A high flow air filter will increase the amount of air flow capable of flowing through your intake. Most of these filters are made out of foam or another similar material. You must up-jet if you install a high flow filter in order to match your increased air with an increased amount of fuel.

High-Compression Head

Cylinder heads can be obtained that increase the compression in the combustion chamber leading to faster strokes leading to increased speeds.

Performance Crank

Installing a performance crank alone does not increase your speed. A performance crank can however influence the carter flow and the combustion chamber size.

A performance crank with full "cheeks" can improve the carter flow. Sometimes there are holes in the cheeks, filled out with nylon or cork. This is done to reduce the weight of the crank, increasing gas reaction but reducing low end torque. This is mostly done on high-rpm machines, since they don't need a lot of low end torque.

Some performance cranks have a shorter shaft that allows for greater or less displacement. Shorter or longer shafts are also used to fit cylinders that are not meant to go onto a specific engine. Although it does not fix the timing-problems, it does fix the piston coming above or too much below the cylinder.

A common mistake is that a shorter or longer shaft would influence the length of the stroke. This is not true. The stroke is determined by where the shaft is connected to the crank, how far it is off centre. The further off centre, the longer the stroke.

Piston Kits

These kits replace your cylinder and piston with a larger bore. Generally, you will also need to re-jet your carburetor to allow a greater volume of fuel/air mix to enter your engine.

They can be done in weekend, and generally give good performance.

However, most kits recommend a 300 to 800 mile break-in period after installation, to allow the rings on the piston to use the fine scratches (call the honing) in the cylinder to gently polish into a smooth, well seated finish.

Over-revving the engine, and showing off your new kit to your friends by throttling all the way up is a sure way to destroy your new kit if it's not properly broken in.

Note that some kits can increase your engine combustion area above 50CC, which may change your moped to a motorcycle due to your state's laws. Make sure to check with your DMV before you spend the money on a kit!

If you want an indication what speed you can get with different types of Puch Maxi cilinders, you can check this out:

Puch Maxi Cilinders

Cylinder Porting

Cylinder porting is one of two arts - the white art of Port Matching, and the black art of Port Reshaping.

See Smitty's full article, as transcribed from the forums, for a guide to cylinder porting from the guy who does it for a living.


By changing the front and/or rear sprocket you can redistribute speed to top or low end depending on your needs. Usually increasing top end with this method decreases low end, and vice versa.

Reed-valve intake

A reed-valve intake has a lot more tuning potential than a piston-controlled intake. Read how to make your own on a Puch engine (and any other engine if you're handy).

DIY reed-valve kit


The stroke has a major part in how an engine performs. It's not easily changed (as it requires a different crankshaft) but some people have managed to machine cylinders to engines with a mis-matched stroke.

Read about a lot of different strokes here:

Moped & Scooter strokes

Really Fast, But Not For Long

Nitrous Injection

Makes you go real fast for up to 5 seconds.

The problem? You run really lean for those five seconds, and every time you use the nitrous, you have a good chance of causing your engine seize from lack of lubrication.

JATO Rocket

A Jet Assisted Take Off unit will make you go really really really fast for up to 7 seconds... straight into a tree. And fry everybody behind you.


Nitromethanol, also known as RC-car fuel is an alcohol based fuel that burns faster and hotter than gasoline. This increases the performance greatly.

But as most people know, alcohol dissolves oil. And oil is what keeps your 2-stroke going. Also the added heat can cause your piston to over expand and instantly seize. So you will need a good lead-replacer (The type that goes into old cars that run on leaded fuel) to insure a good heat-conduction of the piston and cylinder wall. Also you will need special nitromethane 2-stroke oil, so the oil doesn't dissolve.

Don't use more than 15% nitromethane, as it will surely kill your engine. Mix the oil and lead-replacer with the fuel in the right proportions, shake and take for example 850ml's of that mixture and add 150ml's of nitromethane. Start the engine on normal fuel and run it till it is completely warmed up. Then switch to the nitromethane mixture.

Beware: You can't kill your engine by stopping the ignition anymore, the nitromethane mixture is self-combustible under pressure. So make sure you can cut the fuel off at any time!


This category has only the following subcategory.

Pages in category "Performance Tuning"

The following 104 pages are in this category, out of 104 total.