How To Avoid Jet Kit Disasters

A funny thing happened when I tried to re-calibrate my carb...

Okay, so you've decided to install a jet kit by yourself. While it is neither extremely difficult nor complex, there are many things that could go wrong. I've installed about a dozen jet kits on various motorcycles during my misadventures as a bolt-breaking, parts-losing, knuckle-busting do-it-yourselfer, and everything I'm writing about here is something that has actually happened to me.

We'll begin with the removal of the carburetors themselves. At first glance, this seems pretty straightforward. However, to get to the carbs, you have to remove the gas tank. This involves disconnecting the fuel lines, the vacuum line (if there is one), and the cables (throttle and choke).

jet kit parts for Kawasaki Vulcan 1500 Classic
This is the DynoJet kit for the single-carb Kawasaki Vulcan 1500 Classic, with new jets, a different, multigroove jet needle and some of the tools required for installation. Because the replacement parts generally make the bike run richer, installing such a kit may be considered tampering and run afoul of emissions rules.Mike Pons and Stephen Lee

A peek under your gas tank will reveal that the fuel line is held on to the petcock and carbs with very small pinch clips. At this point, take a second to figure out how to remove the pinch clips. Do you squeeze them together and then lift up, or do you need to pull them apart and lift up? I once spent over 15 minutes just trying to get the clip off the fuel line because I assumed it was a pinch-type clip. After the clip is lifted, loosen the fuel line from the fitting with a small flat-head screwdriver and gently pull with a pair of pliers near the fitting. Don't just grab the line and do a clean-and-jerk–type motion. I did this once and I actually pulled the bike off the sidestand and onto its side before I realized that the line wasn't moving, but the bike was. After this, I wondered why they even had those little pinch clips on the fuel lines.

After the line is loosened, remove the tank and carefully hold it with both hands close to your body. The sloshing fuel combined with a clean and waxed tank sometimes makes the tank easy to drop when you walk with it to put it in a safe spot. Don’t ask how I know this.

Airbox removal is next and usually fairly straightforward, although with certain bikes there’s only one way to remove it. Take your time here. If you’re like me, you’ve just spent over an hour removing the fuel tank. In my haste once, I decided to use a Stage 3 jet kit instead of a Stage 1 because I couldn’t figure out how to remove the airbox and wound up using a small Sawz-all to remove it. Needless to say, the airbox removal was not impossible, and the bike was not built around the airbox like I believed.

Jet kit needles
You can clearly see the difference between the stock needle (bottom) and the jet-kit needle. The kit needle has five clip grooves to permit you to set it at different heights (the lower the clip, the higher the needle and the richer the mixture), and it’s much more slender at its business end, which permits more fuel to flow past it.Mike Pons and Stephen Lee

Open-Float Surgery
Once the airbox is removed, the carbs should be free to come off the bike. Drain the gas out of the carbs (either by removing the main jet access plug or opening the drain valve), loosen the clamps on the intake boots, and remove the carbs. I find it easier to remove the cables after the carbs are out of the boots because you can turn them over and get to the cable drums more easily.

Once the carbs are off the bike, set them on a clean workbench and follow the instructions of the kit manufacturer. If you don’t have the proper size Phillips-head screwdriver for the tops of the carbs, go buy one (preferably a T-handle). The Phillips heads are made out of a very soft metal and will round-out easily if the screwdriver isn’t the right size. The factory uses a threadlock agent on the screws, so they don’t come off easily the first time. If you have an impact driver, a couple of very light taps will usually break the screws loose. Do not, I repeat, do not proceed without the proper size screwdriver. If you do, you can count on rounding-out at least one of the screws holding on the carb tops or float bowl. And if you round-out one of the screws, you’ll have to drill out the screw and try to use an easy-out (and in the process, discover just what oxymoron means).

After the tops are off, consult your service manual on the removal of your needle. Some needles are locked in place in the slide and require more than just the “grab the needle with a pair of pliers and pull” technique. A general rule of thumb I use, discovered through numerous trial-and-error experiences, is this: If you’re working at pulling, pushing, turning, or twisting any part on your bike with more than just your teeth clenched, there’s probably an easier and correct way of doing what you’re doing.

modifying carbs without removing them
If you’re careful, you can modify your carbs without removing them completely, as Muzzys’ Mike Wymer demonstrates. Use good screwdrivers of the right size and make sure they have a firm purchase before applying torque. When tightening things down again, don’t over-tighten screws or jets or you may damage the carb body.Mike Pons and Stephen Lee

The Right Hole in the Right Place
At some point you have to drill various parts on the carbs, whether it be the slide or the plug for the fuel-mixture screws. Consult your manual since the diagrams supplied by the kit manufacturer are not model-specific and carbs vary. If you have to drill both the fuel-mixture-screw plugs and the slides, be sure to distinguish which drill bit is for what. The bit for the fuel-mixture screw plug is usually larger than the one for the slide.

Drilling the slides is pretty easy. It usually involves just drilling (with the proper drill bit) one of the holes next to the hole where the needle goes. I have not seen a kit yet that calls for the center hole to be drilled. Be sure all shavings from the slide get cleaned out thoroughly. When drilling the plug for the fuel-mixture screw, be absolutely certain you’re drilling the right plug. Ahem, it would be a shame to drill a hole on the wrong part of the carb because you assumed the fuel-mixture screws were on the bottom just because you saw them there before, and then have to fill it in with a spitball and solder. After locating the proper plug, drill very, very gently and be prepared to stop. The screw usually lies just underneath the plug, and if you mutilate it, it will be very hard to find a replacement; fuel-mixture screws are sometimes not available as an individual part.

jet kit washer
In many cases, a thin washer—around 1mm thick—placed under the clip of the stock needle will improve throttle response, midrange power and, in some cases, even mileage. Most U.S.–spec motorcycles made in the past 18 years suffer to some degree from lean carburetion in the midrange, though it may not be a problem at higher altitudes.Mike Pons and Stephen Lee

Which Setting?
Once you've gotten this far, just follow the kit manufacturer's baseline recommendations for the proper settings. When installing the small e-clips on the needles, I usually take a large clear plastic bag and install them inside the bag. I've been involved in more than one e-clip hunt after the e-clip didn't install properly and popped off the needle and onto the floor and then God knows where. If you plan to fiddle with the settings frequently, you may want to invest in a small supply of e-clips.

After adjusting the carbs to the kit manufacturer’s recommendations, reinstallation is the next step. Guard against haste here. Take your time and work methodically.

diaphragm in jet kit
Handle the diaphragm atop the vacuum slide carefully and be sure that it’s installed correctly and not pinched or torn during installation.Mike Pons and Stephen Lee

You might consider making some changes that make it easier if you have to readjust the jetting on the carbs. Lockhart sells a quick-disconnect coupler for the fuel line that I find invaluable in the frequent removal of the gas tank. It splits your fuel line in two and saves you the trouble of having to disconnect your line at the petcock or carburetor (and thus avoiding the pinch clips that hold the fuel lines that cannot be pulled free by hand anyway). Also, you may want to replace the Phillips-head screws with the appropriate sized Allen-head screws on the carb tops and the float bowls to ensure that you don’t round them out in future adjustments. The screws holding the tops and bottoms of the carbs in place don’t require very much torque at all. I can certify that over-tightening would be a mistake.

After all this is done, you're ready to put the carbs back on the bike. If the carbs don't go back into the intake manifolds easily, spray a little WD-40 onto the inside of the rubber boots and then wiggle them in. Once the carbs are back on, reinstall the tank (some WD-40 on the rubber mounts can help here too), reattach the lines and cables, make sure everything moves freely, and start up the bike. Don't forget to make sure your petcock is on (or set it to prime). It will take a couple of seconds for the bike to start since all the gas was drained out of the float bowls. Once it's started, look for any leaks. If there aren't any, give yourself a pat on the back and take it out for a ride to feel how great a job you did on enhancing the performance of your bike.

jet kit fuel-hose fittings
These quick-disconnect fuel-hose fittings from Lockhart Phillips USA can greatly simplify carburetor or fuel-tank removal and reduce fuel spillage in the process. To install them, cut the line at an accessible point and insert half the fitting in each section and clamp them in place. Then simply snap or unsnap them to separate carb from tank.Mike Pons and Stephen Lee

Do-it-yourselfing is a great way to learn more about the machine you ride. In the process of becoming more intimate with the maintenance and modification side of motorcycling, you'll learn and test your limits. Patience, perseverance, problem-solving ability, self-reliance, despair, frustration, and pride are just some of the feelings you will encounter as part of your bolt-breaking, parts-losing, knuckle-busting do-it-yourselfing.

jet kit disaster-drilling too hard
As almost everyone who has ever done it will warn you, be sure that you don’t drill too hard or too far when removing the mixture-screw cap. Be sure that you’re drilling in the correct place and using the right bit. Clean all shavings out of the carb, since even a tiny sliver can cause a stuck throttle or plug a jet and damage your engine.Mike Pons and Stephen Lee

Some final words of wisdom: Never throw a tool in anger in the garage. Like the toothpaste cap that will find its way into the toilet when you drop it in the bathroom, the tool will find a very expensive part to damage (and, once again, don’t ask how I know this).