Backwater Performance Systems Large Vanguard Mikuni Twin Carburetor Kit 1. Throttle Cable Twin (CKC-41) 2. Carburetor VM30mm (CKC-40) 3. Loctite 242.5mL (A-210) 4. Air Cleaner Filter 6000 (EC-86) 5. Rev Limiter 4350/5100 (CKC-27/15) 6. Intake Manifold Set (CKC-48) 7. Flange VM32 (CKC-44) 8. Air Cleaner Prefilter (CKC-31) 9. Rev Limiter Gasket (CKC-16) 10. Air Deflector (CKC-42) 11. Intake Gasket (CKC-65) 12. Hose Clamp (A-45) 13. Governor Lock 10mm (CKC-12) Bolt ¼ X 1 Hex (F-B42) Washer ¼ L/W (F-W29) Spring Pin 3/16 X 7/8 (F-M11) 14. Butt Connector 12-10 GA (EL-23) 15. Ring #10 16-14 GA (EL-31) 16. Needle & Seat 2.3 (CKC-18) 15. Ring #10 16-14 GA (EL-31) 16. Needle & Seat 2.3 (CKC-18) 17. Cable Clamp 5/8 (RS-02) 18. Bolt 5/16 X ¾ Skt (F-B64) 19. Nut 6mm Flange (F-N29) 20. Washer 5/16 Flat (F-W22) 21. Bolt 8mm X 25mm Skt (F-B76) 22. Washer 5/16 L/W (F-W04) 23. Fuel Hose T ¼ (CKC-43) 24. Jet 180 (CKC-55) 25. Screw 6 X 5/8 Skt (F-S14) 26. Zip Tie (BLC-96) 27. Fuel Hose ¼ (A-43) 28. Cowl (EC-25) Not pictured: 29. Jet 25 (CKC-57) 30. Sprocket 48/46 (STC-51/245) 31. Throttle Cable Lever (CKC-30) 32. Screw 10 X ¾ Tapping (F-S06) Tools required: Hex wrench set 12mm socket 10mm wrench 7/16 wrench Flat head screw driver Philips head screw driver Side cutters Pliers Small round file Wire Crimper Drill
Assembly - Twin Mikuni Remove the front panel by turning the cam screws one full turn. They do not screw all the way out. Remove the entire rear governor and throttle assembly. Remove the air cleaner assembly, rear throttle linkage, carburetor linkage, the carburetor, crankcase ventilator tube and the fuel line. Place a rag in the intake manifold holes. Remove the governor arm.
Install the governor lock. You must lock down the governor shaft so it does not move. First remove the upper snap ring from the gov shaft using snap ring pliers. This allows the governor lock to slide all the way down and close to the engine. Open and slip the snap ring downward. Install the governor block with the slot facing the front of the engine and the split pin under the lock next to the aluminum boss on the top of the engine. Important - Rotate the governor arm shaft counter-clockwise while rotating the governor block clockwise. Tighten the bolt to 25 inch pounds. There should be no free play in the governor shaft. Remove the oil cooler. Remove the bolts as shown here. Remove the 1 outdrive cooler hose. (not shown) Remove the front wire guard and grass screen. Remove the front cowl. If the cowl standoff come out of the block, hold the stud with vise grips and remove the nut from the stud. Blue loctite the studs back into the block. Keep the cowl bolts. You will use some of them later. Remove the head air deflectors.
Very Important Step - Elongate the bottom hole of the two head air deflectors downward 3/16. This will help you locate the holes when you reinstall the panels. Cut the coil wire ties from the intake manifold. Let them hang loose for now. Remove the intake manifold studs. Put them aside. You will not be using them. Remove the stock throttle lever assembly by cutting the assembly with a hack saw. You will need to make a couple cuts. Cut as shown and carefully use a chisel and pliers to split the throttle and remove. This takes a little work so be patient. Remove the stock throttle cable. Install the new throttle and twin throttle cable. Route the cable as shown. Install a wire clip on the engine head to hold the cable in place. If you have a BPS stainless exhaust, route the cable close to the engine near the mounting bracket. Not near the exhaust flange, tube or muffler.
Install the two intakes and intake manifold gaskets. Use the four short 8mm X 20mm socket head bolts. One intake is longer than the other. The short intake installs on the left and the long on the right. Attach the coil wires with a zip tie to the upper air deflector panel as shown. Install the longer cowl bolt into the top of each side of the front cowl facing out as shown with the flange nut provided in the kit. Install the cowl being careful that you don t knock out the small spacers mounted in the cowl face bolt holes. The cowl needs to be slipped under the engine side panels to fit up tightly. Take your time and mount the cowl carefully and completely. Install the cowl bolts. Don t tighten any of them until all are installed.
Install the head air deflector panels. The panels install over the bolts you installed in the front cowl. Double check the cowl mounting to ensure it is fully in place. Early you elongated the bottom holes of the air deflector cover. This will help you install them. Install the grass screen and front wire cover. Install the oil cooler. Install the rev limiter. Place the adhesive gasket on the back of the rev limiter. It provides shock protection and the gasket helps keep moisture out. Mount it on the side of the engine cowl as shown. First raise the handle to see how high to mount the rev limiter. Newer model floating handles raise very high and may hit the right carburetor. If this is the case on your engine, you will need to give up your floating handle feature and tighten the handle bolts to make sure the handle does not come up and it the carburetor. Find the best position for your height and steering style and lock it down. Remove the engine plastic wire cover. Install the rev limiter wires as shown. We want you to cut the wires and install them into the marine heat shrink butt connectors. There are two types of rev limiters. The 4350 rpm rev limiter is for stock motors and the 5100 rpm is for the 45 engine. The red wire clips into the grey engine wire. The green wire clips into the engine green wire. The black wire mounts to the starter bolt as the ground. Use heat from a hair dryer to shrink the butt connector plastic. You will need to test the rev limiter later. Do not rev the engine until you perform the test
Attach the crankcase ventilator tube with a wire tie as shown. Install the intake manifold flange on each side. Put a small amount of silicone sealer on the flange face. Use 8 each of the 15mm long small socket head screws. Do not tighten any of the screws until they are all in place. Snug the socket head screws to 10 inch pounds. Install the intake manifold rubber flanges using 2 ea of the 8mm X 22mm socket head bolts. Loctite in place. Place a small amount of grease on the flange to facilitate mounting. U Install the carburetors. They need to be straight and very tight. Remove the carburetor throttle tube inserts located on top of the carburetor. Install the throttle cable with its inserts. Screw them in to within 1/8 of the bottom. Install the throttle cable by unscrewing the top of the carburetor and removing the round slide. Look down inside the top of the round slide. There is a flat retainer. Do not remove the jet needle. Remove the retainer, insert the large slide spring on the carb cap and while holding the spring back, place the throttle cable end into the slot and move to the center. Reinstall the flat metal retainer. Make sure the bent portion of the retainer is mounted downward and into the cable slot. The large carb spring will hold the retainer in place. Note: Route the throttle cable so that it does not get overheated and burned by the muffler.
Reinstall the round slides. Note: The slide has a slot that must be aligned with the pin inside the carburetor. Install the throttle cable guide on the engine head. Route the cable through the guide. Do not install the air cleaners yet. You need to see inside the carburetors to adjust the throttle slides. It is important to remove any slack from the throttle cable so you will get full throttle. When you squeeze the throttle, the carburetor inner slide front edge should be even with the top of the carburetor intake hole. Remove the slack from the throttle cable by unscrewing one side of the cable extender located three inches from the throttle lever. Additional slack can be removed from the throttle by turning the throttle cable extenders on top of the carburetor. Leave a very small amount of slack so that the cable tension does not affect the idle. The throttle lever has a threaded insert that can turned in and out which will lengthen or shorten the cable housing. The objective is to make sure that the carburetor inner slide moves all the way upward when the throttle is squeezed, but yet, have enough slack in the cable so the engine will return to idle. Synchronize the carburetors by observing the location of each carburetor slide inside the carburetor. Open the throttle with the throttle lever until the slides nearly reaches the top. Leave a small sliver of the round slides showing near the top. Both slides
should be at the same height. You can adjust the height of either by turning the throttle cable insert on top of the carburetor in or out. Once the slides are even, tighten the two jam nuts on the top of the carburetor. Recheck slide height after one hour of operation. Install the air cleaners and air cleaner prefilters. Route the carburetor overflow tubes as shown. Check all fitting and remove all your tools from the engine. If you have a fuel line bulb, gently pump fuel into the carburetor. If not, close the air vent on the fuel tank and gently push down on the tank for one minute. This will act like a large fuel bulb. Depress the choke on each carb and start the engine. Let the engine idle for a minute and turn off the choke. Adjust the idle speed to 1200 rpm by turning the idle screw located on the left side of the carburetor. Test the rev limiter. The stock motor has a 4350 rpm chip and the 45 horse has a 5100 rpm chip. Do not run the 5100 rpm chip on the stock motor or it will cause permanent engine failure. idle screw location Start and warm the engine one minute. Gently increase the rpm to either 4350 or 5100. The engine will begin to surge at this point. Each time you run the engine, take a minute and check to ensure the rev limiter is working. This protects the engine if you hit an underwater object and the prop clears the surface. This will cause an rpm surge and the limiter will make sure the engine does not overrev and cause damage. Idle Speed Adjustment: With the engine turned off, turn each of the idle adjust screws in completely. Turn them back out 6 turns. Then start the engine and set the idle to 1200 RPM. Whatever you turn on one screw, do the same on the other. They should each be in the same position to ensure good idle.
The idle air/fuel mixture screw is located on the right side of the carburetor. It is normally set at 1 and 1/2 turns out. With the engine at idle, turn the screw on each carburetor in and out a quarter turn at a time to get a smooth idle. Whatever amount you turn on one carburetor, do on the other. Route the Rev Limiter Important Information: The rev limiter will turn off the engine if it fails or is damaged. Disconnect the green wire from the engine to start the motor. The rev limiter must be installed correctly with wire down and chip sealed. The wires must be corrected properly. Check the rev limiter often by warming the engine and rev the engine slowly to the rev limit top RPM. Replace immediately if the rev limiter is damaged.
Mikuni Manual: Read the instructions and apply those things you need to know for our application. Jetting is important. Service and Maintenance: Use a new fuel filter and always use good clean fuel. Drain the fuel from the carburetors when you place the machine in long term storage. Adjustment: The Mikuni carburetor is set up at Mud Buddy for best all around performance. We highly suggest you use our tuned stainless exhaust with this system. The Mikuni carburetor has an accelerator, idle, mid range and high speed adjustment. Your carburetor comes with stock jetting and some custom Mud Buddy internal parts. Your carbs are fitted with a 25 idle jet, 180 main jet and stock jet needle and needle jet. Your jet needle height is set to the second lowest C-clip location. The Mikuni carburetor will almost certainly run correctly on your engine as designed and with the installed parts. But if it doesn t, you may alter its tuning to suit your engine s needs and type of conditions you encounter such as load, altitude and temperature. The low speed air screw is normally set at a turn and a half out. Turn it in and out a little at a time to ensure good idle performance. The brass slotted low speed air screw is not used to set idle speed. This is done with the left side screw with spring. Set to 1200 rpm. Warranty: This carburetor may not meet California air emission standards. You will not be provided Briggs and Stratton warranty service if this carburetor is installed at the time you request warranty service. Keep your stock parts. Notice: You are responsible for the use, correct installation and service of this carburetor. Mud Buddy is not liable for installation or any subsequent damage to the motor due to installation, jetting adjustment and maintenance of this carburetor. Tips: We recommend you replace your fuel filter. We recommend you check belt tension and grease the drive. We recommend you use Autolite AP3923 or APP3923 spark plugs. We recommend you use synthetic oil. We recommend you use 91 or higher Octane fuel. We recommend you install a tach on your engine. We recommend you check your rev limiter often. We recommend you use a personal floatation device and the safety lanyard while operating any watercraft. We recommend you use our tuned stainless exhaust and our Tiger Big Blade for best performance. We recommend you let others know your destination and return time. We recommend you carry a cell phone. Be safe and be careful. Remember, return your front engine cowl to Mud Buddy to avoid a core charge. Thank you. Mud Buddy/Backwater Performance Systems, 7945 South, 1530 West, West Jordan, Utah 84088, 801.352.8011, www.mudbuddy.com