Sierra 18-97350 Carburetor Kit | Mercury 9.9-25 HP

When a Mercury 9.9, 15, 20, or 25 horsepower outboard starts hunting at idle, floods on a hot restart, or dies the moment you back off the throttle, the carburetor is usually the culprit. Today's ethanol-blended fuel is hard on the soft parts inside a carb, and they don't last forever. This Sierra 18-97350 carburetor kit gives you everything you need to bring that carb back to life: gaskets, o-rings, seals, diaphragms, and the small hardware that always seems to walk off the bench.

Sierra builds its replacement parts to meet or exceed the original equipment they replace. They supply parts to a lot of the same engine builders and boat manufacturers every day, so you're not gambling on a no-name bargain kit here. The diaphragms are cut to the correct thickness, the o-rings are sized to seat the way they should, and the gaskets seal on the first pull-down. That matters when you've got the cowling off and don't want to do the job twice.

Most of these carbs fail the same way. The boat sits through the off-season with fuel in the bowl, the ethanol pulls moisture and leaves varnish behind, and the tiny metering passages gum up. Then spring comes and the engine won't idle, or it runs lean and hot at cruise. A full kit like this replaces every wear item at once instead of chasing one bad o-ring at a time. Cleaning the carb without new soft parts is a temporary fix at best, because the old diaphragms and o-rings have already taken a set and won't seal like they did new. Do it right and the motor idles clean and picks up crisp again.

A few things we've learned rigging these. First, confirm your exact carburetor model before you start, since a couple of the 25 HP variants use a slightly different diaphragm. Second, wet the new diaphragm before you set it and take your time on the alignment, because a dry diaphragm tears easily. Third, if the fuel pump runs off the same carburetor, replace that pump diaphragm at the same time or the lean condition comes right back. And while you're in there, put on a fresh inline fuel filter and run ethanol-rated fuel line so you're not back at the bench next season.

One heads-up on the hardware. The kit includes the screws and small pieces most of these rebuilds call for, but a few tiller-handle setups use slightly different length fasteners. So keep your old hardware until you've confirmed the new pieces thread in clean. It's a five-minute check that saves a headache.

You don't need a shop full of specialty tools for this job. A clean bench, a set of screwdrivers, some carb cleaner, and an hour or two of patience will get most boaters through it. Lay the parts out in order as they come off, snap a couple of phone photos before you disassemble, and the reassembly goes smooth. It's a very doable job for anyone comfortable turning their own wrenches.

These smaller Mercs show up on everything from tiller-steer jon boats to sailboat kicker motors, and access behind the cowling can get tight on the 15 and 20 HP models. Give yourself room to work. One honest caution: if the engine has cracked pulse lines or a warped carb body, a rebuild kit won't fix that. Sort out the hard parts first, then this kit handles the soft parts.

For a Mercury 9.9 to 25 HP outboard that's earned a tune-up, this is the kit that gets it running like it should. A carburetor rebuild is one of the highest-value jobs you can do on a small outboard, since it restores fuel economy, easy starting, and reliable idle for a fraction of the cost of a shop visit or a new carb. Order before 3 PM ET and we'll ship it same day on in-stock units.