Dirt Bike Jetting 101

A correctly jetted carburetor makes a tremendous difference in the torque, mid-range pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike’s power-band.

A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. Hard starting when hot or cold, poor response when opening the throttle, reluctance to idle, all of these are symptoms of an improperly sized pilot jet or incorrectly adjusted air screw.

The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using.

Dirt Bike Jetting 101

A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It’s all in the jetting. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, leading to deposits and wet fouling of the plugs.

Do you have spooge? There are the rare instances where a mechanical issue, such as a leaking wet-side crank seal, can cause spooge. But, by and large, this isn’t the case. In most instances, spooge is caused by rich jetting. It has nothing to do with how much oil you mix in the gas, or how hard you ride. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, resulting in deposits, plug fouling, and spooge. Spooge is nothing more than unburned fuel and oil entering the exhaust.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless. Someone with a good understanding of jetting can get you in the ball park, but you need to do the testing to determine the correct jetting yourself if you want it right.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it’s best.

It’s very important that you start with the pilot circuit, because the pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to re-jet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel.

One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don’t seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.

Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.

All jet testing must be done with the engine at full operating temperature.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the air screw slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Is It Rich or Lean?

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet. If your engine doesn’t respond to air screw changes, then you either have a dirty carb, or the pilot jet is way too rich. When the pilot jet is way too rich, you are forced to use the idle screw to open the slide so far in order to keep the engine running that the pilot circuit is partially bypassed, and the engine is actually starting to draw fuel through the needle jet.

Once you have determined (and installed it if it’s necessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it’s time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day.

Now, it’s time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn’t really any way to test the needle other than by feel, but it’s usually quite obvious when it’s right or wrong. A too-rich needle can often be felt simply when revving the bike on the stand. The bike will sound rough and raspy when blipping the throttle on the stand. A correctly jetted bike should rev cleanly and crisply.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Please note that, when reading plugs, the tip of the insulator, threads, etc. are meaningless for jetting purposes. They can tell you a lot of things, but jetting isn’t one of them. Only the mixture ring at the very base of the insulator, inside the threads, can tell you anything about the jetting.

The slide is also a tuning variable for jetting, affecting the throttle range from 1/8 throttle to approximately 1/3 throttle. If you can’t clean up the small-throttle jetting on your bike no matter how lean you go with the pilot or the needle, the slide is the next step. But few bikes need leaner slides.

Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit.

Two-strokes have an air screw that you screw in to make the jetting richer, and screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer. Their purpose is the same, they just do it in different ways.

-Thanks to Chokey over at ThumperTalk.

Motocross & Dirt Bike Carrier AMC400 Single Aluminum Review


It’s nice to be able to haul your dirt bike to the track… But what if I don’t have a pick-up truck or trailer? Instead of going out and spending hundreds on a trailer (or possibly thousands), I can get a single Motorcycle/Dirt Bike hitch carrier that mounts to the hitch of my vehicle. That’s right, I can throw one on the back of my ghetto race-van to haul my motocross bike to the track, and still have plenty of room to haul gear and parts! Unfortunately, you can’t just buy or build any kind of bike carrier and expect it to last forever. This is how I found the AMC400 single Aluminum Motocross Bike Carrier.

Single Aluminum Dirt Bike Carrier

I like simple things, and this fits right into that category because I don’t have to take the time to hook up a big trailer, load my bike, make sure the lights work, check tires, and what not. It’s even easier that tossing my dirt bike in the back of a pick-up because I only need myself to load it, and now I have that extra room for gear, parts, tools, and passengers if I’m driving the van!

What To Look For When Buying A Dirt Bike/Motorcycle Carrier

  • Number of bikes it can hold
  • Weight limit
  • Material its made of
  • Ease-of-use
  • Durability
  • Quality of build (are things where they should be)
  • How much it weighs

How Many Bikes Are You Hauling?

If you’re transporting two bikes or more then you’ll need a Double Motorcycle Carrier or trailer, unfortunately. If you’re hauling one bike, then the AMC400 dirt bike carrier is what you’re looking for. It’s the perfect set-up if you’re an individual going out for a day of practice or racing.

Will It Sound Like A Shaker?

Weak and poorly built carriers will shake and rattle, making it sound like you have someone banging on a tin can. Although this dirt bike carrier is made of aluminum, it is sturdy and will hold bikes that weigh up to 400 lbs safely. It’s able to do this with light-weight aircraft aluminum. The main hitch tube, though, is powder-coated steel so it doesn’t twist or bend.

No Spending A Night In The Shop To Prepare…

Wouldn’t you rather do things quickly to get out and ride, rather than spending hours fixing or putting something together? I know what I would rather be doing, and unless you’re a workaholic, I bet you want the same. Fortunately for us, the AMC 400 bike carrier can be put together in just minutes. That will allow you to get in more riding, and relieve some frustration. Once it’s together, just shove it in the hitch receiver, load your bike, and you’re off!

Lightweight, But Will It Last??

Aluminum is much lighter than steel, so the same volume of it will weigh less. But, the same volume of aluminum as steel will not be as strong. So, the compromise of aluminum is: light and flimsy, or strong and bulky. There is also a happy medium, and AMC has it figured out for their single dirt bike carrier. It is light and not too bulky, yet strong enough to carry your full-size dirt bike across the country. Although it can’t haul a street motorcycle, carrying your dirt bike on this will save you time and money. It’s much cheaper than a trailer, and the weight and wind resistance are minimal, giving you more MPG’s in your vehicle!

What’s Included?

  • Single aluminum dirt bike carrier
  • Reverse anti-tilt device
  • Loading ramp features a full width, welded attaching lip with 2/3″ hook
  • Aluminum ramp that mounts on carrier

Limitations?

  • Carriers up to 400lbs safely
  • Hitch Weight Limit: Most Class III hitches are rated for 500 lbs Most Class IV hitches are rated for 1000 lbs
  • Vehicle hauling capacity: May be restricted to by your vehicle (check dealer or manual)
  • Will not work with class II or smaller receivers
  • NOT recommended for tow-behind trailers including 5th wheel trailers & camping trailers
  • NOT recommended for use with hitch adapters / extensions
  • Not scooters/mopeds

Does It Include Warranty?

Yes, the AMC-400 comes with a 1-year warranty.

What Are Others Are Saying About the AMC 400 Single Motocross Bike Carrier…

This dirt bike hitch carrier is getting many great reviews from buyers, and has 4.5 out of 5 stars on Amazon.

Here are some comments in it to date:

  • Great carrier for the money
  • When you don’t want to pull the hauler…
  • Off to the races
  • Awesome bike hauler
  • Good for the price
  • I love it
  • Light ramp that works

Any Complaints?

Some people had trouble loading and unloading their bikes because the carrier rail is a little narrow for some tires, and the carrier itself is relatively short. But, someone found a solution to unloading the bike without having a heart attack. The dirt bike is quite high when on the carrier, so for average to shorter riders it can be difficult to pull off if you aren’t very strong. So instead of pulling the bike off the carrier backwards, put the ramp in front of the bike. Then start the bike and put it in gear. While leaning the bike towards you, slowly release the clutch, allowing the bike to ride safely down the ramp.Another tip for loading the your bike is parking right up to a ledge or curb so you don’t have to push the bike up as high to the carrier.

Where Can You Buy The AMC Dirt Bike Hitch Carrier?

You can buy this Single Motocross Bike Carrier from Amazon. Currently they offer free shipping for this item within the continental 48 states.

Click Here To Buy My AMC-400 Dirt Bike Carrier

Where Can I Read More Reviews For the AMC 400 Aluminum Motorcycle Carrier?

The best place to read reviews  Amazon from people who actually bought this carrier is Amazon. Click here to read more.

-Tom Stark