Yamaha 9.9 Carburetor Air inlet

[Franziska]

Hi,



just cleaned the carburetor on our 2015 Yamaha 9.9 High thrust 4stroke outboard.



When disassembling it I noticed a fair amount of a sand like substance in the main yet, cleaned it and the motor is working fine. I tasted it, it wasn't salty.



Still, I was wondering where that stuff came from.

Can it be coming in via the air inlet?

We have a fuel filter/fuel water separator in the fuel supply line.



We have occasionally some of that very fine Sahara dust in the air.



Two questions :
1) Main air inlet

The main airtake seems to only have a very coarse metal grid to prevent bigger particles from getting in, no foam filter.

Would it be good to stuff some open air filter material into the air inlet, or will the outboard not get enough air then?



2)Tiny air inlet in carburetor

Secondly I noticed two manufactured very small air holes under the metal plate shown in attached image. There is a channel system underneath this plate and I found some "sand" there too. Suspect that's where it's coming in.

Why is there no filter, does it make sense to somehow fix something spongy in front of these inlet holes to prevent clogging in the future?



Btw. the carburetor shown is not the same we have, just similar.

[rslifkin]

No air filter is common on marine engines, as the manufacturers figure it's not a dusty environment. It's possible you sucked some sand in via the air intake, but on most outboards it would be tough to get sand into the cowl and then into the air intake without it settling out along the way.

It's also quite possible that whatever the sandy substance is precipitated out of the fuel and that's why you're only seeing it in the carb.

[thinwater]

You meant to type "main jet."


I have had several Yamaha 9.9s over the years, am a chemical engineer, and have researched this in the lab and field. Also led a working group in ASTM to develop the test methods. So I'm pretty sure. I've also used these approaches in the field for 20 years, without a single carb problem. Before that I had epic problems (I could pull the carbs and clean them underway, I did it so many times!), which of course, created the interest in finding solutions.



This is aluminum corrosion products, the result of galvanic corrosion between the aluminum body and brass jets. This is encouraged by the water absorbed into e10, which makes gasoline into a weak electrolyte.


There are two ways to prevent this.

• Keep the gas dry. If it is a portable tank, keep the vent closed when not running If installed, use a silica gel vent filter.
• Use an additive proven to stop e10 corrosion. I only know of 3 that are well-tested for this (some can actually make it worse). Biobor EB, Stabil 360 Marine, and Merc Quick-Store.

This is a short version on my blog. The long version is in Practical Sailor.
---
I assume you meant the fuel jet. Of course, you may have dust from the air as well, given the location. That is beyond my experience. Is there dust inside the cover and inside the inlet horn?







[One of my 9.9s. See the pitting (deep)? That is where the grit is coming from.]