DR350 - MIKUNI CARB CONVERSION - THE VINTAGE BIKE BUILDER

Suzuki DR350 Pre-Jetted Carburetor Conversion
Installation Instructions

NOTE: This manual is provided as technical reference tool to assist experienced mechanics in the installation of the Niche Cycle, DR350 Mikuni carb kit. This manual in no way replaces the experience and skill necessary to safely and property install a motorcycle carburetor. It is assumed these kits will only be installed by professionally trained motorcycle mechanics. Niche Cycle, The Vintage Bike Builder and all associated parties accept no liability for any damage, or injury resulting from the incorrect installation or maintenance of any carburetor. Please use this guideline at your own risk.

The DR350 - Mikuni TM33 Conversion Kit is a very straight forward carburetor upgrade for the DR350. With these instructions, anyone with basic mechanical skills and a few tools can tackle the job. The TM33 has a built in fuel pump which provides unparalleled throttle response. And being a Mikuni, quick starting and easy maintenance are always present. Unlike the OEM Mikuni carburetor, replacement parts for this carb are readily available.

1999 DR350 with electric start

Fitment
This kit will fit all models of the 1990-2001 Suzuki DR350. This kit was designed to replace the stock Mikuni CV carb that came with DR350SE (electric start models) beginning in 1994. However, all DR350s can benefit with the use of the TM33.

NOTE: While other models are very similar; these instructions apply specifically to the DR350 electric start models. The test bike used for these instructions was a 1999 DR350SE. If your bike is not the same year or model, you might find slight differences, but the installation is basically the same.

A socket set like this will set you back less than $15 at Harbor Freight and can be ordered online if there isn't a store near you

The Tools you’ll need
Make it easy on yourself and use the right tool for the job. If we’re very specific about a tool, it’s because using anything else will eventually cost you time and money. If you don’t have the right too, get it and save yourself a lot of aggravation. If you try to use tools like an adjustable wrench or a vice grip, you’ll round-off the nut or bolt and have to replace it. With metric tools so cheap and available on Amazon, eBay or Harbor Freight, it’s just penny wise and pound foolish not to get the right tool.

One of the best tools you can use is a cell phone or digital tablet. Professional mechanics used to draw a lot of diagrams, but these days, they take lots of pictures. Some keep a spiral bound notebook handy for taking notes. These notes and pictures save a lot time and frustration on projects – especially when you are disassembling something you are unfamiliar with.

If you own a motorcycle, you should have all of the tools listed below and more to maintain your bike. Rather than list the individual sockets or wrenches, I have put them down as kits, because that’s how they are normally sold. You won’t need all the wrenches or sockets for this just, but it makes more sense to buy the kit than buying these tools individually.

Here is a list of tools and items you will need:

A flat blade screwdriver set
A Phillips-head screwdriver set
Metric Hex Key (Allen wrench) set
Metric combination wrench set (6mm-19mm)
Metric socket set (6mm-19mm)
Razor knife (for cutting hose)
Plastic prying tool (see note below)
Needle nose pliers

Primary disassembly

To avoid creating sparks around fuel, be sure to disconnect the battery

Remove side panels using a #3 Phillips screwdriver.
Disconnect the negative terminal for the battery using a screwdriver, 8mm or 10mm wrench (depending on battery bolts).
Remove the two bolts securing the rear of the seat with a 12mm wrench. Lift the seat from the rear, and pull back to remove it. These bolts can be found just above and behind the air box.
Turn off the fuel at the petcock. If the fuel line still has the factory clamp, use a pair of pliers to squeeze the clamp and move it down the fuel line about two inches from the petcock. Twist and pull the fuel line down to remove it.
Place a rag and a small container under the carburetor. Open the drain screw in the bottom of the float bowl, allowing fuel to drain into the container. If the screw is frozen in place, don’t worry, you can drain the fuel from the float bowl later (see examining fuel below).
Remove the carburetor vacuum line from petcock.
Using a 10mm socket, remove the two bolts securing the base of the fuel tank. With the bolts out, lift the tank slightly and pull backwards to remove it (photo upper right).

Removing seat bolts

Safety Note:
Handle all fuels with extreme care in a well-ventilated area. Gasoline is highly flammable and extremely dangerous. Drain fuel using great care. Do not allow any smoking or electrical sparks nearby while transferring fuel. Do not leave fuel in open containers unattended. Don not allow children to handle fuel.

Creating room to remove the carb
Like most modern, dual-purpose bikes, the DR packs a lot of components into a very small space. By temporarily relocating a few components, you can give yourself more room to work. Following the steps below will make the job faster and lot less frustrating.

Moving the shock fluid reservoir out of the way makes it easier to remove the stock carb

Give yourself more room on the right side of the carb by moving the rear master cylinder reservoir out of the way

Loosen the two bolts on the rear shock reservoir with a 12mm wrench or socket. Move the reservoir out of the way (photo top left). You can suspend the reservoir from another location by looping a long wire tie through the hole in the mount and around the frame.
On the right side of the bike, loosen the 10mm bolt that attaches the rear master cylinder reservoir to the frame. Pull the hose and reservoir back between the frame and exhaust (photo top right). Use a long wire tie to hold the reservoir upright and out of the way. If you don't have any wire ties handy, a section of metal coat hanger, a piece of welding rod or a length of wire can be used as well. Be careful not to stretch or damage the brake line. If the line appears to be damaged, this would be an excellent time to go ahead and replace it.
The coil is located on the right side of frame backbone, just above the carburetor. Using a 10mm wrench or socket, remove the two bolts securing the coil. The coil doesn't need to be disconnected, just moved out of the way. It's a good idea to support the coil with a long wire, tie wrapped around the frame, or by using a piece of wire holding the coil up. This will stop the wire connections on the cable from being unnecessarily stressed.
Using a #2 Phillips screwdriver, loosen the carburetor manifold hose clamp and the clamp securing the air box boot to the rear (intake side) of the carburetor (photo top left).
The air box boot, which connects to the intake bell of the carburetor, can also be temporarily moved out of the way, rather than removed. Being careful not to damage it, grasp the air box boot and carefully pull the boot back and to the left, allowing it to rest on the frame member away from the carb

Removing the coil bolts allows room to route the throttle cables

Removing the carb and manifold

Use a 10mm open-end wrench to loosen the adjusting nuts on the top and bottom of both throttle cables. These nuts also secure the cables to the routing bracket, located above the bellcrank on the carburetor. With the cables loose, you can rotate the bellcrank on the carb and this will allow you to remove the rear cable from the carburetor bracket. Lift the front cable out of the bracket and remove the cable end from the bellcrank as well (top photo right).
Using a #2 Phillips screwdriver (photo right), loosen the carburetor manifold hose clamp.
Double check to be sure there are no remaining vacuum lines or connections that will interfere with the removal of the carburetor.
Grasp the rear of the carb at the intake bell and pull rearward while twisting slightly to the right side. When the carb pops out of the rubber manifold, remove the carb through the right side. Note: if you haven't removed all the fuel from the float bowl, try to keep the carb upright until you can get it over a suitable container for draining.
Using a hex head (Allen) wrench, remove the two bolts securing the intake manifold to the cylinder head.
If you are going to be pausing work on this project for any length of time, place a clean, balled up piece of heavy duty paper towel or a small, clean rag in the intake port of the cylinder head. This will keep dirt, debris, bugs or hardware from getting in the opening and potentially ruining your engine.

NOTE: It's always a good idea to retain original parts - like the carb and throttle cables. If you decide to sell the bike, the new owner may prefer using the original components. It's also possible that in the future you may need to inspect the original parts for reference information. For this reason, it's a good idea to drain the fuel from the carb and dry it out with compressed air. Once you have removed the fuel, pack the stock carb and original cables away. Don't forget to label the box or container.

With the adjusting nuts loose, you will be able to remove the throttle cables from the carb

Loosening the intake manifold clamp to facilitate carb removal

Notes on fuel:
Because of possible fuel contamination, we always recommend you drain any existing fuel from your fuel tank before installing a new carb kit. One of the main causes of carburetor failure is contaminants in the fuel and you don't want to mess up your new carb with dirty gas. If you question whether or not your fuel is dirty, empty about a cupful from the petcock into a perfectly clean, white plastic or clear glass container. A white container is best because it allows you to easily see any sediments in the fuel. Place the container on a level surface, in a well-ventilated area and let it sit for about 30 minutes (make sure there are no nearby open flames, electrical sparks and that no one is smoking). If after 30 minutes, you can see sediment on the bottom of the container (no matter how small), you will need to change your fuel and clean your fuel tank.

A suggested method of cleaning the tank is to first empty the tank of all fuel (see notes on transferring and storing fuel below). Then put several good sized drops of Dawn dish washing detergent (it is best at breaking down oil and fuel) into the tank. Fill the tank about half way with water and vigorously swish the tank around. Empty the fuel tank and rinse it out thoroughly with a garden hose. Be sure you protect the tank from scratches by setting it on a rubber mat or thick towel. After draining the tank of all water, be sure to blow the tank dry with compressed air. The tank MUST BE completely dry before adding new, clean fuel. If you are transferring fuel into the clean tank from a fuel container, make sure the container is clean and there are no sediments floating about in the container.

The best way to transfer fuel
Transfer fuel only in a well-ventilated area. If you haven't done it already, disconnect the battery on the motorcycle. Make sure the petcock is in the 'OFF" position. Attach two to three feet of 1/4 inch hose to the barbed end of the petcock. Make sure the hose is secure and will not come off easily. If necessary, clamp the hose. The hose will be running from the petcock to a fuel container on the ground, so the length of the hose my vary depending on your particualr need. Be sure the container you are using to catch the fuel is designed to safely hold fuel. Also, make sure the container is large enough to hold all your fuel. In other words, don't use a 1-gallon container if your tank holds 2.5 gallons. Turn the petcock on and stay with the container until the tank is empty. Once empty, turn off the petcock, remove the hose and cap the continer. DO NOT SMOKE anywhere near the bike when transferring fuel or moving the container. Also, avoid any sparks while transferring fuel.

Removing the throttle cables
These procedures cover removing the stock cables and replacing them with a slightly longer cable set required for this kit. Both the old and new cable sets are push/pull-type cables. One cable pulls the throttle open with the other returns the throttle to the closed position.

Grasping the top ends of the cable, carefully fold back the rubber boot that covers the area where the throttle cables enter the twist throttle housing. This will provide you with a little more clearance near the elbows in the cable. You can easily slide the smaller diameter cable out of the boot, but the larger cable is more difficult to get out. Spray the inside of the boot and cable with WD40 or silicone. Now you will be able to carefully slide the boot off the larger cable. Take care not to damage the boot.
Loosen the two Phillips-head screws that hold the throttle housing halves together.
Remove the screws completely and carefully separate the two halves.
Before you remove the cable ends, take a few moments to carefully observe how the throttle control halves fits together with the cables. This will save you a lot of trouble later. You may even want to snap a few pictures with your mobile device. You will see on each cable there is a U-shaped tab that fits into a designated slot on both sides of the housing. Note that the rounded sides are positioned to the back of the slot while the flat fronts face each other. This is shown in the photo to the right. Be sure to make a note of where the tab fits on each cable. Also make note of which side the smaller diameter cable is located.
Lift the housing halves away from the plastic twist throttle base (this is covered with by rubber hand grip) and carefully remove the barrel cable ends from the hand grip. This can be done by rotating the cable until it lines up with open slots in the twist grip. Slide the ends out of the twist grip and remove the cables.
Before you remove attempt to remove the old cable, take a moment to note how the cable is routed. You will see the cables run up from the carb, along the backbone of the frame under the tank, up the gooseneck of the frame, under the instruments and finally out to the handlebar end.
The cable ends are fairly large, so it might prove easier to first remove the headlight cover and loosen up the instrument cluster. This is done by removing the three Phillips screws that hold the plastic headlight fairing in place. Next, use a 12mm wrench to loosen the two bolts securing the instrument cluster. Without removing the cluster, you can fit the cables between the bars and the cluster.
Before removing the old throttle cables, first make sure there are no cable ties securing the cables to the frame.
With the cables released from the frame and the instrument cluster loose, pull on on the handlebar end of the cables and slide of the cables up between the instrument cluster.

This photo shows the rubber boot rolled back at the throttle. The screws and on the base of the throttle

The tabs on the cables are indicated by the arrows. The round part of the tabs fit into the back of the housing with the front of one tab will face the other tab

A close up of the tabs on the cable. They will only fit one way

With retaining bolts loosened, the instrument can be moved back to let the cable ends through

Upper installation of new throttle cables

With the old cables removed and out of the way, place the throttle ends of the cables into the boot you just removed from the old cables. Spraying the inside of the boot with WD40 or silicone with make inserting the cables easier.
With the new boot in place, route the new cables down between the instrument cluster and the handle bars to the right side of the frame. Just below and behind the headstock (goose neck) there is a welded wire cable retainer. Route the cable through this bracket and behind the heat shield welded to the frame. Continue routing the cables over the engine, toward the carburetors.
As mentioned before, Suzuki uses a push/pull cable system on the DR models. While the cables look similar, they are not the same. The U-shaped tab welded onto the cable fitting (mentioned above) can only fit one way into the halves of the twist throttle housing. First examine one of the cables to see if it will fit properly in the bottom (push) side of the twist throttle housing. It should be obvious if it won't work. If that cable won't fit in the housing, exchange that cable with the other one. Place the U-shaped side of the cable fitting into the slot on the bottom half of the throttle housing. You can't make a mistake as the cable will only fit one way.
Place the barrel fitting from that cable into the closest recess on the twist grip and fit the raised end of the twist grip into the corresponding groove in the bottom half of the housing. With the barrel end of the cable in the twist grip, rotate the grip counterclockwise, a small amount, until the recess for the other cable is exposed outside of the housing half.
Place the barrel end of the other cable into the open recess on the twist grip. Route the cable along the groove in the twist grip in the opposite direction of the first cable (see photo above)
Place the tab of this cable into the top half of the throttle housing.
Place the top half of the housing around the twist grip e and hold the sections together until you can replace the Phillips-head screws removed earlier from the housing.
Tighten these housing screws just a couple turns leaving the housing halves loose.
Slide the twist throttle assembly, with the cables now connected, onto the handle bar.
Make sure the throttle cables exit the assembly at the top of the bar and in front of the mirror.
Grasp the carburetor end of the cables and test the motion by turning the twist throttle a few times. When the throttle is opened, one cable goes up the other retreats. The opposite action occurs when the throttle is closed.
If everything checks out properly, roll or slide the cable boot down the cables and over the end of the throttle housing.

With the boot over the cable end, route the cable set between the instrument cluster and the handle bars toward the engine

In this photo the push cable is inserted into the recess in the twist grip

In this photo the barrel end of the "pull" cable is seated in the correct recess and the halves are ready to be joined

Nylon pry bar set from Harbor Freight

Manifold and carburetor installation

Clean the intake manifold surface on the cylinder and the intake adapter. Suzuki uses an O-ring rather than a gasket, so these surfaces should be relatively free of debris.
If you placed a paper towel or rag in the intake port of the cylinder head to protect it, remove it now.
Niche does not supply an O-ring to replace the one in the stock manifold. If the O-ring appears dry or flattened, then order a new one from Suzuki and replace it before installing the kit. These O-rings usually hold up well and shouldn’t need replacing.
The Suzuki intake adapter tilts up slightly and is designed to fit only one way. However, it is also possible to put it on upside down, which can cause you extra work. So, care must be taken to be sure it's installed right the first time. Take a moment to examine the face of the rubber manifold adapter (the side that faces the carb). You will see there are two, rectangular, rubber protrusions sticking out from the front edge of the adapter. There is a small space between them. These protrusions are highlighted by arrows in the photo on the upper right. If you look at the top of the engine-side spigot on the TM33, you will also see a small, single, rectangular, aluminum casting protruding from the top of the spigot. With the hose clamp in place but loose, put the rubber manifold adapter onto the intake bell of the TM33 making sure the rectangular casting on spigot fits between the two rubber protrusions on the manifold adapter. This is how you can be sure the manifold is fitted correctly (photo right). Tighten the hose clamp on manifold adapter.
Working on the left side of the bike, hold the carb on its side and insert the carb (with the flange adapter mounted) into the space behind the cylinder (picture above right). Rotate the carb horizontally so it faces the cylinder. After that, rotate the carb vertically and into the correct position (photo top next page).
Place the new manifold spacer behind the existing manifold (photo right). The fiber gasket goes behind the spacer. Secure this combination to the cylinder head with the two 6 x 26mm screws which are supplied with the kit. Be sure to snug each bolt up evenly before fully tightening them. Also, make sure the gasket is properly in place before tightening. You can do this by threading in the screws just a few turns and then pulling the carb and spacer back to see if the screws are inserted through the holes of the gasket. When everything is in place, secure the screws.
Taking care not to damage the air box boot, carefully pull it back toward the rear of the bike and tuck it back inside the frame and onto the intake bell of the carburetor. Line up the boot as close as you can with the intake bell of the carb. Use a plastic pry tool to eliminate any areas where the boot is folding inside the edges of the intake bell. Harbor Freight makes a very inexpensive nylon pry bar installer set (item # 69668). One of the tools has a smooth pointed end and it can be very useful when fitting air box boots. If you try to use a screwdriver to fit the boot in place, you take a real risk of tearing the boot (which is expensive and a pain to replace). If you can get most of the boot to sit in place on the intake bell and there is just small piece that won't drop over the lip, then there is a nifty trick you can use to get the boot to seat fully: Try pressing on the center of the boot with your thumb (see photo on right). This may take several attempts from slightly different angles to work. Unless the boot is really stiff, pressing on it in this manner will normally allow the front of the boot to pop into place over the intake bell. Do not attempt to fit the hose clamp on the boot until after you have the boot properly seated (see step 8). The clamp will get in the way and provide unnecessary aggravation, because it can be put on after the boot is installed.
If you are having trouble fitting the boot in place, you can remove it and let it soak in hot water for several minutes to add flexibility. Do not apply excessive heat directly to the boot (flame or heat gun. Once installed, use a flashlight to examine all sides of the boot to ensure that it is in place. Make sure there are no gaps. If the boot has gaps around the intake bell or at the air box, sand and debris can enter the carb, which can quickly ruin the engine.
With the boot fitted properly in place, remove the screw from the hose clamp. Spread the clamp open enough to fit around the boot taking care not to bend it sharply in the middle. Slide the clamp around the boot and secure it after replacing the screw.

The factory, rubber flange adapter mounted to a new TM33. Notice the rubber tangs (protrusions - shown by arrows) on opposite sides of the of a raised casting in the center of the intake bell on the TM33

With the factory flange adapter mounted to the carb, insert the carb from the left side of the engine like shown, then rotate and turn into position

The prototype spacer shown in this photo was aluminum colored. The spacers included with our kit are now gold anodized.

Air box boot seated properly and hose clamp in place. Avoid any gaps when seating the boot

Installing and adjusting throttle cables

With upper part of the throttle cables already in place, (see Upper installation of throttle cables, steps 1-13), twist the throttle forward to the closed position. Look at the end of the throttle cables near the carburetor. With the throttle in this position, the cable with the most free play (longest end) is the pull cable. The other is the push or return cable.
Grasping the pull cable, screw the top nut to the last thread nearest the elbow, and loosen the bottom securing nut, running it to the bottom of the elbow. This will leave about one inch of space between the nuts. The cable bracket on the top of the carburetor will fit between these nuts.
Looking at the bellcrank on the carburetor (pictured to the right), the end of the pull cable will fit in the rear recess of the bellcrank and the push cable will fit in the recess to the front (see photo on right).
Turn the bellcrank forward with one hand. Place the barrel fitting on the end of the pull cable in the rear recess of the bell crank, with the other hand. Turning the bellcrank forward will allow more access to the rear recess
With the barrel end of the the pull cable secured in rear recess on the bellcrank, route the inner cable (wire) through the grove on the bellcrank and up to the rear bracket. Center the space between the securing nuts between the bracket. Leave the nuts loose for the time being.
Place the barrel fitting on the end of the push cable into the recess on the front side of the bellcrank.
Using the same technique as the pull cable, place the push cable into the cable mount (photo right).
With the cables loosely in place. gently twist the throttle and see if the cable fully opens the throttle (bellcrank) on the carburetor and returns it. With the twist throttle fully open, attempt to turn the bellcrank in a clockwise direction. If it doesn't move, you are are opening the throttle fully. If the bellcrank moves, adjust the cables to allow more play as needed.
With the throttle fully closed, check for slack in the pull cable. Remember, there are two adjusters on the pull cable. One is near the carburetor; the other is up by the handlebar (see photo right). Use these adjusters equally to remove any slack in the cable. Make absolutely sure you do not advance the bellcrank at all. This will open the throttle on the carburetor and raise the idle. Ideally, you want the bellcrank fully closed (all the way counterclockwise), with the cable snug, but not pulling on the bellcrank.
With the slack removed from the pull cable, check for any slack on the push cable. The push cable has just one adjustment and that is at the end of the cable near the carburetor.
With throttle cables connected and securing nuts snug; once again, operate the twist throttle and double check the motion of the bellcrank for complete, end-to-end movement.

With throttles cables in place, this photo shows the location of the push and pull cables

This photo shows the location of the recesses on the bellcrank where the barrel- end of the throttle cables are placed

Cables in place, but securing nuts not yet adjusted.

Completing the installation

If you removed or lifted up the fuel tank, replace the fuel tank and secure using the correct bolts.
NOTE: We highly recommend you replace the old fuel line and clamps; install good quality fuel filters; clean the fuel tank; and refill the tank with new, clean fuel. Image how difficult it would be to set up the tuning on your new carb if the chambers were getting clogged by crud in your fuel tank. So, consider replacing these items a time saver.
Using new clamps, secure the new fuel line to the fuel tank and carburetor.
Reinstall the shock reservoir, the rear master cylinder and coil removed earlier.
Reinstall the battery and connect the terminals.
Reinstall the seat and seat bolts
Replace air filter element and reinstall the side panels. NOTE: We highly recommend replacing the air filter element with a good quality product. If a dirty or clogged filter is used, this will limit air flow into the carburetor causing a enriched fuel/air mixture.
If the Headlight was loosened to provide access to the throttle cables, reinstall the bolts holding the headlight in place.
Put fuel in the tank and check for any leaks.
Double check all components removed from the bike to ensure everything has been reassembled.

A reminder about fuel:
When putting on a new carb, we highly recommend cleaning your fuel tank and replacing the fuel with new, high octane fuel. After years of use, sediments can find their way to the bottom of fuel tanks and eventually into the carburetor. You don't want this to effect the performance of your new carb so make sure the gas is clean! See "Notes on fuel" above.

Being imprinted on clear plastic, it's sometimes hard to see, but the arrow on the filter indicates the flow of fuel. If the filter is on backward, it won't work properly.

The color of the insulator can provide and excellent report on the fuel/air mixture

Initial start and tuning
You could start your bike at this point and chances are it would run okay. But if you stopped here, the bike probably wouldn’t run to its full potential. This next step doesn’t take that much time and it will ensure your bike is running properly. Tuning and jetting is individual to every motorcycle. Some bikes have more wear than others. Some may be fitted with aftermarket pistons, cams, exhaust or air cleaners. These changes effect a bike’s jetting set up. Not only should your bike idle smoothly with a new carb, you should also make sure the fuel mixture entering your intake manifold is correct for your bike. A fuel mixture that is too lean will sometimes make your bike feel like its performing better, but it can also going to run at a very high engine temperature and ruin your engine very quickly. A mixture that is too rich can sometimes protect the engine from damage, but will also make the bike run poorly. The best way to tell if your mixture is spot-on is by the color of a new spark plug after testing the bike under certain conditions for a few minutes.

Take a look at the color of the ceramic insulators in the photo to the right. The spark plugs with bright white insulators are indicating a lean condition, or not enough fuel. The dark or sooty plugs are indicating too much fuel in the mix. The plugs in the middle are a nice caramel color. They indicate the correct fuel mixture. Ideally, you want your plugs to be this color.

When we ship these carb kits, they are jetted for stock bikes ridden in an altitude range between sea level and about 3500 feet. If a bike has been modified with performance parts or if it is ridden at higher altitudes for any length of time, it will probably need jetting correction. If your bike is mostly stock (no performance cams or exhaust system) and you do most of your riding at an altitude below 3500 feet, then this kit should already be properly jetted for your bike. Keep in mind, you'll still need to adjust the idle and mixture screws.

For customers who have made performance modifications to their bikes, it's a good idea to begin testing your jetting with the jets we've already installed. Your bike will run with these jets and they will provide you with a baseline for correction. Please follow the steps below:

If your bike was running okay with your old spark plug, you may leave it in for the time being. If the plug is fouled (black or sooty in color, you should replace it).
Temporarily adjust the air/mixture screw by first gently tightening the screw in all the way. Do not over-tighten this screw or you could damage the seat for the screw. Once in all the way, back the screw out 1-1/2 turns.
Start your motorcycle. After a minute or so of warm up, let the bike settle to an idle. If it does not idle, try turning in the idle screw until the engine can maintain a smooth idle.
With the bike at a smooth idle, slowly begin backing out the air/mixture screw. The idle should rise a bit. Continue slowing backing off the air/mixture screw until the idle peaks. When it does, turn the idle screw in ¼ turn.

Checking the Jetting:
On a Mikuni round-slide carburetor, there are four ways to adjust your fuel/air mixture:

The pilot jet - Also known as the slow jet, this jet controls the fuel/air mixture at or just above idle. The idle mixture is further controlled by the air mixture screw mentioned above.
The slide cutaway - The cutaway in the throttle slide begins working the moment the throttle slide is lifted. The larger the cutout on the slide, the more air that enters the fuel/air mixture.
The needle jet and jet needle - These two items work together to control the mixture in the mid range
The main jet - This jet controls the fuel air mix for the top 25-percent to full throttle.

Checking the jetting at idle:

Warm up the bike and install a new spark plug (correct type recommended by the manufacturer). With the engine warm, start the bike without using the choke. Let the bike idle about five minutes. Do not rev the engine. Keep the engine at idle speed the entire time. Remember you are only checking the idle circuit and only one circuit can be checked at a time.
Shut the bike down with the key or kill switch (do not choke to stop it) and let the engine cool for a few minutes before you remove the spark plug.
Check the color of the insulator on the spark plug. If it’s bright white, you’re not getting enough fuel in the mixture and you’ll need a larger pilot jet. We include a larger jet with the kit. If it’s just slightly white, you can try screwing in the air mixture screw about ½ to 1 turn and run the test again with a new plug. If the plug is dark in color, you’re getting too much fuel and you’ll need to restrict the fuel flow at idle with a smaller jet. There is one included with the kit, but we sell all available sizes for this carburetor.
Similar procedures can be preformed to check the mid-range and top end. To find out more about these procedures, please go to our Mikuni Tuning and Jetting Manual.

Suzuki DR350 Pre-Jetted Carburetor Conversion Installation Instructions

Suzuki DR350 Pre-Jetted Carburetor Conversion
Installation Instructions