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.]

[Franziska]

Originally Posted by 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.]

Thanks,

regarding air, I meant the main air intake "Air horn" as you call it, and on my carburator, there is this square stainless steel plate held in place by three screws. Underneath it is a kind of air channel labirinth with a small air inlet and I presume outlet of similar small size at the other end of the labirinth. I could see that on, what I presume is the tiny air inlet side, there was a fair amount of these beige colored sand like particles, similar to the ones I found in, what I presume is the main jet.

The small outlet side was clean.

I did not notice any pitting.
The carburetor is half a year old. Still I never took it apart up to now and the engine was working flawless so far.

Wondering if it could be some casting sand particles. The carburetor is a Chinese made copy of the original Yamaha part. Costs 10% of the Yamaha part and is identical but might have run through fewer quality controls.


Regarding the water in the fuel, will add some additive. Mix enough for our 120L tank into a 5L can and then pour that into our main 120L stainless tank.

Btw. someone suggested that high grade clean alcohol would do the same but would be cheaper and easier to find. Is that true?

Thank you for your input.

[Franziska]

Originally Posted by 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.

Thank you, we will add an extra large in-line fuel filter now right before the fuel intake.

[Jammer]

Thinwater speaks my mind on this.


I had the same Yamaha 9.9 for four years. One fact to consider is that the idle air passage is extremely small and hidden, and clogs easily leading to mixture problems at idle. It's hidden under a cap you have to pry out that covers an adjustment screw that the EPA doesn't want you to adjust (hence the cap). That all has to be taken apart for a thorough cleaning.


I also have seen what I believe are aluminum corrosion products clogging jets in outboards with unimpeachable fuel filtration even though I only use non-ethanol gasoline. I have started using Stabil Marine 360. Time will tell.

[Franziska]

Originally Posted by Jammer

Thinwater speaks my mind on this.


I had the same Yamaha 9.9 for four years. One fact to consider is that the idle air passage is extremely small and hidden, and clogs easily leading to mixture problems at idle. It's hidden under a cap you have to pry out that covers an adjustment screw that the EPA doesn't want you to adjust (hence the cap). That all has to be taken apart for a thorough cleaning.


I also have seen what I believe are aluminum corrosion products clogging jets in outboards with unimpeachable fuel filtration even though I only use non-ethanol gasoline. I have started using Stabil Marine 360. Time will tell.

Thank you. Idle air passage is the keyword I was missing.

Yes, it's tiny and yes it was clogged up.
Wonder if the particles went in there.



As a remedy I wonder if one could carefully glue a small piece of an open cell sponge over it, which could act as a filter. Taking care not to block it by getting the glue on the actual hole.



If you need to clean it just rip the sponge off.



Would that work?

[Shrew]

A carb rebuild kit should cost around $50 USD and includes replacement jets.

You can try removing the jets and soaking them in carb cleaner for about 24 hrs then blowing them out with a can of carb cleaner. Sometimes its just easier to rebuild the carb and replace the jets.

disassemble the entire carb, removing all the gaskets and o-rings. Soak the parts in a gallon of carb cleaner overnight, then blow out the parts and reassemble with the rebuild kit.

[Jammer]

I don't think I'd want to try the sponge, it may disintegrate and create the problem it is intending to prevent.


I believe constant use of Stabil Marine 360 is probably the best preventative measure.

[Franziska]

Originally Posted by Shrew

A carb rebuild kit should cost around $50 USD and includes replacement jets.

You can try removing the jets and soaking them in carb cleaner for about 24 hrs then blowing them out with a can of carb cleaner. Sometimes its just easier to rebuild the carb and replace the jets.

disassemble the entire carb, removing all the gaskets and o-rings. Soak the parts in a gallon of carb cleaner overnight, then blow out the parts and reassemble with the rebuild kit.

Thanks, I have already cleaned it, works fine. I was only wondering where the particles come from and possible remedies to prevent them from getting in again.


Further I was wondering what these tiny air inlets are.
They are the idle air passage I have learned now.

[boatpoker]

Judicious use of Tef-Gel on all dissimilar metals will greatly reduce or eliminate galvanic corrosion and the resulting aluminum oxide dust.

[barnakiel]

Given the small orifices of the carburetor and the big orifice of the cowl, you may be better off adding some fine mesh material there.


I often wonder what happened to our engine when we started it on a kalima day ... it probably got very clean inside cylinders ... very soon ... (???).


Yes marine environment is not dusty - most of the time.


cheers,
b.

[Franziska]

Originally Posted by barnakiel

Given the small orifices of the carburetor and the big orifice of the cowl, you may be better off adding some fine mesh material there.


I often wonder what happened to our engine when we started it on a kalima day ... it probably got very clean inside cylinders ... very soon ... (???).


Yes marine environment is not dusty - most of the time.


cheers,
b.

Good point. Just added a kitchen sponge inside of the cowl inlets.
Will see if that helps.
Thanks and all the best from Napoli.

[GordMay]

Did you notice an unusual accumulation of yellow[ish] dust, on your decks?
July, 2024 had a higher than average SAL dust cover, which may have been [some of] the source of your carb' problems.

The Saharan Air Layer [SAL], also known as Saharan Dust, is made of aeolian mineral sand, dirt, and other dust that is lifted, a couple of miles, into a dry adiabatic layer, in the atmosphere, from the vast desert area, that covers most of North Africa.
This dust is carried in the African Waves, which push westward into the Atlantic Ocean, toward the Caribbean, Florida, and the Gulf Coast.
These dust clouds are not uncommon, especially during the months of July and August.
Dry air mixes into the middle and higher levels of the atmosphere, preventing [or substantially reducing] the ability for tropical storms and/or hurricanes to develop.
NOAA estimates that more than 180 million tons of dust leave the African continent, every year.

[Franziska]

Originally Posted by GordMay

Did you notice an unusual accumulation of yellow[ish] dust, on your decks?
July, 2024 had a higher than average SAL dust cover, which may have been [some of] the source of your carb' problems.

The Saharan Air Layer [SAL], also known as Saharan Dust, is made of aeolian mineral sand, dirt, and other dust that is lifted, a couple of miles, into a dry adiabatic layer, in the atmosphere, from the vast desert area, that covers most of North Africa.
This dust is carried in the African Waves, which push westward into the Atlantic Ocean, toward the Caribbean, Florida, and the Gulf Coast.
These dust clouds are not uncommon, especially during the months of July and August.
Dry air mixes into the middle and higher levels of the atmosphere, preventing [or substantially reducing] the ability for tropical storms and/or hurricanes to develop.
NOAA estimates that more than 180 million tons of dust leave the African continent, every year.

And we spent November to March in Tunisia, right next to the desert....