Why Use One?The big advantage in using an over-the-counter jet kit is that all the homework has been done for you. Prior to the advent of kits, jetting was a by-guess-and-by-golly occupation. Many times you'd have to special order things like needles and needle jets. If you guessed wrong, it was back to the parts counter, and you'd have to wait weeks until the new stuff arrived. Jet kits remove the guesswork, and because they contain adjustable needles and a variety of jets, they allow you to fine-tune the fuel/air ratio to your exact requirements. Included in most kits is also a tech number with a real, live person on the other end to answer any questions that may arise. In most cases, there is also excellent online information available. In particular, the Factory Pro Web site (www.factorypro.com) is very good-an hour or two there can teach you an awful lot about how carburetors work and how to tune them.
What Won't A Jet Kit Do?Obviously, a jet kit won't repair a damaged engine. If your mill is low on compression, has a cracked intake boot or worn spark plugs, you can install jet kits until you're blue in the face and they won't change a thing. By the same token, if your otherwise properly running bike suddenly develops a case of "won't-idle syndrome" or manifests some other carburetor malady all by itself, chances are good that the problem is the result of something ingested, like water or a piece of dirt that's made its way into one of the jets. If that's the case a jet kit won't help nearly so much as a good cleaning.
Installing The KitCarburetors are no more complicated than any other mechanical device. They do, however, have some small, delicate parts, and as such are vulnerable to rough handling and contamination from dirt. So you'll need to work on them with deliberation and in a relatively clean environment. Essentially, you'll need a clean, dry place to work, preferably with a nice, solid workbench, where you can lay out the parts and a selection of hand tools. A can of aerosol carburetor cleaner and silicone spray or WD-40 will come in handy, too.
The job can be broken down into four steps: removing the carburetors; disassembling them; installing the kit and reassembling the carburetors; and reinstalling them on the bike. While the design of a few bikes will allow installation of a jet kit with the carburetors in place, that's a rarity. Especially since 90 percent of the time, the job entails drilling out the anti-tamper plugs placed over the pilot jet adjusting screw (see sidebar for details).
The first job will probably be to remove the carburetors from the bike. Your shop manual will detail the exact procedure, but as a rule you'll need to remove the fuel tank, remove or disconnect the airbox-to-carburetor hoses and then remove the carburetor cables before loosening the carburetor manifold hoses and pulling the carbs loose. The carburetor manifold clamps usually have smallish, easy-to-strip Phillips-head screws holding them in place. A sharp number 1 or 2 Phillips and a little elbow grease should get them loose, so don't be afraid to bear down. If any become truly buggered, replace them during reassembly. As an alternative, many foreign-car specialists stock thin worm drive clamps in the appropriate diameters with either Allen-head or slotted screws that are more attractive and somewhat easier to work with than the cheesy OEM stuff. Make sure to mark the location of any fuel, water, vacuum or emission lines you've removed before you disconnect them from their ports as well as the routing of throttle cables. You'll also find it easier to drain the float bowls with carburetors still in place as opposed to sloshing fuel all over yourself by removing them full.
Removing the carbs from their manifolds can be a little tricky, as the rubber tends to glue itself to the carbs. If the carbs stick, try rocking them back and forth while spraying a little silicone or WD-40 at the joint. Once the carbs are off (don't forget to plug the intake and airbox openings with clean rags) and the float bowls drained, it's a by-the-numbers exercise.
Some bikes have more carburetors than others. If you're working on multiple carbs, I suggest you complete all jetting changes first, then flip the carbs over and make all needle/spring changes, just to avoid confusion.
1 Start by removing the float bowl. You can expect the screws to be tight and easy to strip. I like to replace them with Allen-head screws (available at most hardware stores) on reassembly.
2 Before going any further, make sure you know which jets go where. The main jet should be in the center of the bowl, with the pilot jet off to one side. Be careful around the floats; rough handling could change the setting, which upsets the jetting. If the floats need resetting, the instructions and your manual will show you how.