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I've got a 2008 Tohatsu 9.8 HP four stroke outboard. My low speed jet keeps getting fouled and on several occasions, I've found yellow almost crystalline "growths" for lack of a better word inside the carburetor. They look like tiny sulfur crystals, and crumble into incredibly fine powder if you touch them. Since everything's been soaked in gasoline, there's no way to smell the powder to see if it is indeed sulfur or not.

Tohatsu Carburetor

I use alcohol free gasoline (now, but there's still a mixture of gas with ethanol and mostly ethanol free) in the tank. I use both Marine Sta-Bil & Startron in my fuel. The fuel runs through several filters including a Racor Fuel/Water separator and there's nothing evident in the fuel if I run it into a clear glass jar right at the carburetor inlet.

The boat sits in a marina in brackish water, fairly close to the river inlet into the bay, so it's mostly salt water.

I've got the carburetor soaking in dip right now, and new jets and gaskets on order. I've gotten so good at removing and cleaning my carburetor I can do it in about 40 minutes now. I almost always find the low speed jet plugged with something. I can't blow whatever it is out, I have to use a fine piece of wire to dislodge whatever it is (I'd assume a glob of the yellow stuff, but can't really tell, it's so small).

Any ideas? Any ideas on how I can prevent it in the future? This isn't the first time this has happened.

EDIT: Yesterday 30 April 2016 I reinstalled the carburetor and the engine ran just fine, although it didn't seem to want to settle down to an even idle, but it only died once while it was still cold. I applied a little choke to make the mixture a bit more rich until it warmed up a bit, then ran it at idle for about 20 minutes or so. After that, I pulled the fuel connector and ran the carburetor dry. I probably won't be back for a weekend or two which is about how long it's taken in the past for the crystals to show up.

The experiment begins, cross your fingers...

EDIT: 06 Jun 2017 It's been a long time getting back to this, we didn't take the boat out for a very long time due to various medical problems my wife & I experienced in the interim. That said, the last time I was at the boat (and ran the engine), I ran the fuel out of it as suggested. Several weeks ago we took it out for a short sail and had absolutely zero problems with the outboard. We ran the carburetor dry on that occasion as well and I hope to continue with this new behavior. I'd like to unlearn how to clean the carburetor so quickly in the future.

Thanks for the suggestions and help, my wife & I appreciate it.

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    Seems like a DIY or automotive group would be a better place to ask.
    – Carey Gregory
    Commented Apr 25, 2016 at 23:17
  • Does the boat get left unused for long periods of time?
    – Nick C ♦
    Commented Apr 26, 2016 at 13:08
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    Yes, sometimes, especially over the winter, however, the precipitate can show up within a couple of weeks. So far I've only gotten stuck on the water once and needed a tow to get in safely. The engine will run on the high speed jet, but I have no desire to come into my marina at 4-1/2 - 5 knots with 3 tons of sailboat, nor do I want to be shifting at 1800-2000 RPM which is about as low as I can idle it when this happens.
    – delliottg
    Commented Apr 26, 2016 at 14:38
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    Those are gasoline additive deposits (which are in all gas blends) and are normal after the gas evaporates in the bowl. Best prevention is to run the carbs dry before storage.
    – Moab
    Commented Apr 26, 2016 at 22:50

1 Answer 1

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Those are the remnants of gasoline

When you let gasoline evaporate it leaves behind various elements within the gas that can't dissipate through evaporation.

These remnants can clog various galley's in your carburetor as well as clog jets.

Even if you are soaking your carburetor you will still want to physically clean out the jets and use compressed air to ensure there is no buildup plugging the various circuits within the carburetor body.

You can use thin copper wire strands to poke through jets. Hold them up in the light and look through them to ensure you have removed any debris that may be blocking them.

In the future, as @moab states in his comment, you will want to run the carburetor float bowl dry after use to prevent this from occurring again.

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  • I got the new parts last night & I'll put the carburetor together for this weekend. Do you have any idea how long it takes for the gas to evaporate from the bowl (ball park)? I ran the outboard fairly hard for a couple of months during crab season last year and then not nearly as hard for just going out sailing, but never had a problem until the boat sat for an indeterminate amount of time. I'm just wondering how long that might be.
    – delliottg
    Commented Apr 27, 2016 at 15:06
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    @delliottg It's hard to say how long it will take evaporation to occur. That carb body looks very similar to a motorcycle carb. There should be a screw on the side so you can drain the carb after each use if you think you won't be using it again for an extended period. Variables such as being in the sun will increase the temperature of the carb thereby accelerating evaporation. Evaporation rate will also be determined by your climate (cold or hot). Best practice would dictate you drain the float bowl using the small drain screw that, I believe, should be on the side of it.
    – DucatiKiller
    Commented May 1, 2016 at 19:12
  • The drain screw is there, but I've never used it for it's designed purpose (yet). I suspect as sailing season warms up (literally), I'll be using the boat enough that I won't see the problem, but I want to see how well it runs next time I get down there after running it dry. Plus at the end of the season I'll use the drain plug to see if I can prevent it from happening over the winter.
    – delliottg
    Commented May 1, 2016 at 21:32
  • +1 for draining the carbs if you're going to get let it sit. Even with Sta-Bil in the tank, you'll have fewer problems if you simply shut off the gas and drain the carbs before leaving the boat sit for an extended period. And the amount of gas you drain out is so small, I'd suggest draining the carbs every time you think there's even a slight chance you won't be using the boat for a couple of weeks.
    – TMN
    Commented May 2, 2016 at 16:07

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