How to Clean & Rebuild Yamaha 90HP Outboard Carburetors

Need help cleaning and rebuilding the carburetor on a Yamaha 90HP outboard? We’ve got you covered.

All the necessary steps to clean and rebuild the carburetor(s) on a Yamaha 90HP outboard motor are listed below. 

NOTE: We used a Yamaha B90TLRX model for this walkthrough, but the procedure is virtually identical for most Yamaha outboard models with carburetors. 

Watch the Yamaha B90TLRX carburetor clean and rebuild video above, and follow the step-by-step guide below to get this job done. 

Yamaha 90HP outboard carb clean rebuild

Tools and Parts Needed - Yamaha B90TLRX Carb Cleaning

Tools

  • Ratchet and extensions
  • 10mm swivel socket
  • 10mm thin wall socket
  • Assorted screwdrivers
  • Dead-blow hammer
  • Pliers
  • Pick tools
  • Impact driver 

Parts

NOTE: The Yamaha B90TLRX has three carburetors, so you'll have to get three carburetor repair kits. You can purchase OEM Yamaha carburetor parts individually, but it's cheaper to get the complete Yamaha carburetor repair kit that includes everything you need for this job. 

Removing the Carburetors From a Yamaha B90TLRX Outboard

Step 1. Unfasten the two latches and remove the top cowling.

Step 2. Remove the four screws holding the silencer cover, followed by the cover itself.

Yamaha 90HP outboard carburetor cleaning

Step 3. Remove the two bolts holding the bracket to the front of the oil tank.

Yamaha B90TLRX carburetor clean and rebuild

NOTE: There's a ground wire attached to the lower of the two bolts which you'll need to remember to reattach when you reinstall the bolts.

Step 4. Remove the carburetor throttle linkage from the right side of the carburetor assembly. The linkage is held in place by three pop-pins, and can be removed simply by pulling it away from the carbs.

Step 5. Remove the six bolts from the bracket that hold the carburetors to the intake manifold.

Yamaha 90HP carburetor rebuild

Step 6. Disconnect the vacuum hose located on the right side of the powerhead; the fuel hose on the left side of the powerhead; the vacuum hose on the underside of the carburetor assembly; and the oil linkage from the left side of the bottom carburetor. 

Watch the clip below to see how to perform this step. 

PRO TIP: To avoid removing the fuel enrichment assembly on the left side of the carburetor assembly — which would allow debris into the carburetor  follow the next step as described.  

Step 7. Disconnect the fuel enrichment assembly's blue wire from the right side of the engine, and the black ground wire bolted to the lower left side of the engine block.

Watch the clip below to see how to perform this step.

PRO TIP: Use a ratchet, extension and a 10mm swivel socket to access the ground wire bolt.

Step 8. Remove the carburetor assembly from the outboard. 

NOTE: You'll see that the three carburetors are NOT identical. The bottom carburetor has an input for the oil delivery system; the center carburetor has the fuel enrichment starter assembly; and the top carburetor has neither of those things.

Yamaha 90 outboard engine carb rebuild

Step 9. Remove the remaining fuel hose assembly that is still connecting the three carburetors.

Yamaha 90 outboard motor carb clean rebuild

PRO TIP: Be careful when removing the fuel hose assembly, as the various hoses become brittle over time. If you damage a hose or any are already split or torn, they must be replaced.

Cleaning & Dismantling the Carburetors From a Yamaha B90TLRX Outboard

NOTE: In this section we will work on a single carburetor at a time.

Step 1. Thoroughly clean the carburetor with contact/brake cleaner. 

PRO TIP: Removing as much dirt and debris as possible will minimize the chance of debris entering the carburetors when they are disassembled.

Step 2. Remove the four screws and the float chamber from the underside of the carburetor.

Yamaha 90HP outboard carburetor float chamber

PRO TIP: If the four screws are difficult to loosen, place a screwdriver over each and hit the screwdriver with a hammer to "shock" the screw threads and break them loose. If that doesn't work, use an impact driver to break the screws loose.

Step 3. Remove the old float chamber gasket.

Step 4. Remove the screw holding the float arm pin, followed by the float itself.

Yamaha outboard 90HP carb rebuild

Step 5. Use a pick tool to remove the float needle valve and its clip from the float.

Yamaha  outboard motor carburetor rebuild

Step 6. Inspect the float for signs of wear or damage, and replace it if necessary.

Step 7. Remove the needle valve seat from the carburetor using a 10mm thin wall socket. Note that there's an O-ring on the end of the needle valve seat.

Step 8. Remove the rubber pilot jet cap, and unscrew the pilot jet from the carburetor.

Yamaha 90HP outboard engine carb rebuild

Step 9. Unscrew the metal main jet cap and the main jet itself from the carburetor.

PRO TIP: The pilot jet and the main jet in older carburetors can often seize in place. To help free them, apply penetrating oil and let it sit for a few minutes before unscrewing the jets.

Step 10. Thoroughly clean the pilot jet and the main jet by squirting carb cleaner though them. Make sure the jets are completely clean and there is no dirt or debris blocking them.

Step 11. Squirt carb cleaner though the pilot jet, main jet and float needle valve channels within the carburetor body to remove any dirt particles from them.

Yamaha outboard engine 90HP carb clean

Step 12. Blow every channel and hole in the carburetor body with compressed air to ensure they are completely clean and clear.

Step 13. Remove the pilot screw and inspect it for pitting or wear, and replace it if necessary.

Yamaha outboard carburetor cleaning

Rebuilding the Carburetors on a Yamaha B90TLRX Outboard

Step 1. Reinstall the pilot screw and tighten it until it bottoms out, then back it off by one and a quarter turns.

Yamaha 90 HP boat motor carb rebuild

Step 2. Reinstall the pilot jet into the carb, and install a new rubber cap (included in the Yamaha carburetor repair kit) over the pilot jet.

Step 3. Reinstall the main jet into the carb with the end with the hole through it facing outwards, then reinstall the metal cap.

Yamaha outboard motor carburetor jet

PRO TIP: Don't overtighten the pilot or main jets, because they're made of brass and can be easily damaged.

Step 4. Install the new O-ring over the new float needle valve seat (both included in the carburetor repair kit), then install the new O-ring/valve seat into the carb.

Yamaha outboard carburetor rebuild and clean

Step 5. Install the new clip (included in the carburetor repair kit) into the float.

Yamaha carburetor float clip

Step 6. Attach the new float needle valve (included in the carburetor repair kit) to the clip in the float.

Step 7. Reinstall the float into the carburetor so the float needle valve slides into the float needle seat, then reinstall the screw that holds the float arm pin.

Step 8. Install the new float chamber gasket (included in the carburetor repair kit) onto the float chamber.

Yamaha 90HP boat motor carburetor rebuild

Step 9. Reinstall the float chamber onto the carburetor, followed by the four screws.

Step 10. Repeat the cleaning, dismantling and rebuilding processes for the other two carburetors.

Step 11. Reinstall the fuel hose assembly that connects the three carburetors. 

NOTE: Replace any sections of hose that are worn, split or torn.

 Yamaha outboard motor carb clean and rebuild

Reinstalling the Carburetors onto a Yamaha B90TLRX Outboard

Step 1. Reinstall the six bolts into the carb bracket, and lay the bracket down with the bolts pointing upwards. Next, thread the carburetor assembly down over the bolts.

Yamaha 90 outboard engine carburetor rebuild

Step 2. Lift the carburetor assembly/bracket and reinstall it over the intake manifold. Tighten the upper bolts first so they will support the weight of the assembly.

Yamaha 90HP carb clean and rebuild outboard

Step 3. Reattach the vacuum lines, electrical cables, the fuel line and the oil linkage. 

Yamaha B90TLRX outboard carburetor rebuild

Watch the clip below to see how to perform this step.

Step 4. Reinstall the carburetor throttle linkage to the right side of the carburetor by pressing it back into place.

Step 5. Reinstall the two bolts holding the bracket to the front of the oil tank (don't forget the ground wire attached to the lower bolt).

Step 6. Reinstall the silencer cover, reattach the top cowling and you're done.

Carb clean and rebuild Yamaha 90HP outboard

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