Performance FAQ

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How can I make my moped go faster?

There are many ways to make your moped go faster than it does right now. Some ways are easier than others, some ways are cheaper than others, and performance upgrades are cheaper and easier on some mopeds than on others.

Pre-speed

Before you turn your moped into a blastin' machine, you need to make sure that it is running properly. This will reduce the number of things that could possibly be wrong with it when you start adding parts later. "Running properly" includes:

  • Clean carb -- even if you think your carb is clean, you should still know how to take it apart and change the jet. (More info)
  • Inline fuel filter/fuel line -- adding a fuel filter will help keep your carb from getting clogged in the middle of a ride. If your fuel line is cracked or brittle, replace it.
  • New, properly gapped spark plug -- get a few spark plugs and keep them on hand. You'll need them later. Don't forget to gap them. (Video)
  • Good tires and tubes -- those two little bits of rubber are all that separate you from becoming a smear on the pavement. Do you trust 30-year old rubber, especially at speeds over 25mph? Replacing your tires and tubes is HIGHLY recommended.
  • Clean points -- if you have points, clean them. It's not hard. (More info)
  • Clean exhaust pipe/exhaust port -- take off your exhaust pipe and make sure it's not clogged with carbon. If it is, take it apart and clean it. Also check the exhaust port for carbon buildup. (More info)
  • Good compression -- check the compression on your moped and compare it to the specifications listed in the manual. If it's too low, your moped won't run very well. (More info)
  • Good brakes -- going fast is fun, but you need to be able to stop yourself too. If your brakes are worthless, try tightening the cable adjusters, deglazing the brake pads/hubs, and/or getting new brake shoes.
  • Tension your chain properly -- you want about 1/2 to 1" of up-and-down travel on your chain. A chain that is too tight will slow you down and a chain that is too loose can disengage itself from the sprocket.
  • Make sure your wheels are perfectly true. see the article Wheel Truing for more info.
  • Air leaks (or lack thereof) -- air leaks are bad. Swarm them, Destroy them.

Free speed

Free speed modifications are modifications that do not involve buying moped parts. However, some of these modifications may require tools that will cost money unless you've already got an impressive arsenal of tools, and not all of them are recommended for beginners.

Got a Puch? Read this thread for an excellent run-down of free (or very cheap) things you can do to increase performance.

  • Clean and repack wheel bearings -- repacking your wheel bearings helps reduce rolling resistance, which can help you go faster.
  • Mill your head -- milling the cylinder head will increase compression and improve your low-end power
  • Remove any restrictions -- this will depend on your moped, so do some research. A common restriction on Puch mopeds is the addition of two small pipes that block part of the exhaust. (Derestricting a Puch Maxi exhaust)
  • Increase air flow -- many people use pantyhose as a homemade high-flow air filter, or they remove/modify restrictive stock metal mesh filters. It is important to increase fuel flow when you increase air flow, or else you risk seizing your engine.
  • Port your cylinder -- this is not recommended for beginners. See Smitty's Cylinder Porting Guide for more information.
  • Change your timing -- on some mopeds, advancing the ignition timing can result in an increase in speed. It can also blow a hole in your piston if taken to extremes, though, so be careful.

Bought speed

Bought speed modifications = performance parts that you buy and install on your moped. Some brands of mopeds have lots of performance parts that you can buy (Puch, Tomos, Motobecane, Honda, Minarelli, Peugeot) some mopeds have a decent selection of performance parts (Garelli, Morini) and some mopeds have zero support in the performance parts department (Batavus, Jawa). Brands with fewer parts can still be made fast, but it takes more time, knowledge, and creativity to make things work instead of bolting them on.

Please read the Performance tuning article.

How fast will I go if I get a _____?

42.7 MPH.

(That was a joke.)

Top speed depends on many factors, including but not limited to:

  • The parts you buy for your moped
  • How well the parts are installed on the moped (ie -- no air leaks, port matching if applicable, etc)
  • Tuning

The spreadsheet is an excellent place to look to get an idea of the combination of parts, the work required, and the carb jetting you'll need in order to reach your desired speed.

What exhaust should I get?

Different exhausts have different speed characteristics. Some are built to give you better acceleration but won't increase your top speed as much, while others are built for top speed but can kill your acceleration. If your brand of moped doesn't have its own exhaust review page, try searching the forums for reviews of exhaust pipes for your moped.

Please remember to UPJET when you add a performance exhaust.

What size jet do I get?

When adding performance parts to your moped, it is very important to maintain the proper fuel/air ratio. Any part that increases air flow through your engine (and most performance parts will do this in one form or another) will almost always need to be accompanied by a corresponding increase in fuel, usually referred to as upjetting. Failure to increase fuel flow can result in engine seizure. You increase the fuel flow by replacing your main jet with a larger main jet.

To know what size jet you need:

  1. Find out what size jet you have. You will have to take apart your carburetor and look at the number stamped in the jet to know what size you currently have.
  2. Buy a range of jet sizes that are larger than what you currently have. For example, if you have a Bing carburetor with a 58 main jet, you could buy sizes 60, 62, and 64. It is a good idea to use the spreadsheet to verify this range, especially if you are adding/modifying more than one part at once.
  3. When your jets arrive at your door, install the largest size you ordered.
  4. Run a plug chop.
  5. Downjet if necessary (if you were lean, order more jets)
  6. Repeat steps 4 and 5 until your plug chops show the desired color.

Note that correct jetting is dependent on many factors. Air leaks, differences in parts or part installation, temperature, altitude, engine, model, and other variables can all alter your jetting needs. This is why it is very difficult for someone on an internet forum to pinpoint the exact jet you will need and why it is recommended that you buy a range of jets and determine for yourself which size works best for your situation.

Where can I buy _____?

Some of the larger and more commonly mentioned suppliers of performance parts include:

There are many (MANY) other excellent moped parts suppliers though, and it is always worth looking through their websites to see what they have.