How to Make a 9.9 Outboard Faster


The four-stroke 9.9-horsepower outboard is the one of the smallest of the mid-horsepower-range outboards from Evinrude/Johnson. Its frame is that of the 8-horsepower outboard and its powerhead, except for the carburetor, is that of the 15-horsepower outboard. Making your 9.9-horsepower Johnson outboard faster doesn't need to involve work that's exacting and requires expensive equipment. You can achieve the desired result by swapping out the 9.9's carburetor for the 15-horsepower carburetor.

Things You'll Need

  • Phillips screwdriver
  • Shop rags
  • No. 24 Torx screwdriver
  • 3/8-inch thin-wall socket
  • Plastic scraper
  • Gasket, from an Evinrude/Johnson gasket kit
  • Torque driver.
  • Twist the boot of the No. 1 spark plug wire and pull the boot from the plug. Wrap a piece of masking tape around the wire and mark it as the wire to the No. 1 plug. Repeat to remove the plug wire from the No. 2 spark plug. You do not need to mark this wire.

  • Loosen the hose clamp that holds the air hose to the air horn using a Phillips screwdriver. Loosen the single retaining screw on top of the air horn housing and lift the air horn from the engine.

  • Place shop rags below the fuel line. Compress the spring-loaded clamp that secures the line to the carburetor and push the fuel line from the nipple on the right side of the carburetor. Use a No. 24 Torx screwdriver to loosen the choke cable clamp and remove the choke cable from the link on the carburetor body.

  • Remove the flange nuts from the carburetor using a 3/8-inch thin-wall socket. Unsnap the throttle linkage as you lift the carburetor, carburetor gasket and insulator from the powerhead.

  • Remove the insulator from the carburetor, set it aside and scrape away any gasket material remaining on the mating surface of the carburetor using a plastic scraper to avoid damaging the surface.

  • Place a new gasket on each side of the carburetor insulator, without using gasket sealing compound. Place the insulator and gaskets over the carburetor studs on the powerhead.

  • Settle the carburetor over the studs. Snap the throttle linkage into place

  • Thread the carburetor flange nuts into place by hand. Tighten to 90 inch-pounds, using a torque driver. Secure the choke cable to the link, then into the clamp. Tighten the clamp to 84 inch-pounds.

  • Reposition the air horn on the powerhead and tighten the retaining screw on top of the housing snugly. Push the air hose onto the horn and tighten the hose clamp. Compress the clamp on the fuel hose and push the hose onto the carburetor's fuel nipple. Slide the clamp over the nipple until it snaps into place.

  • Squeeze the fuel primer bulb and check the system for fuel leaks.


  • Evinrude/Johnson Repair Manual -- 2.5- to 250-Horsepower Models, 2002-2007; Seloc Marine
  • Photo Credit Thomas Northcut/Photodisc/Getty Images
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