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Honda B100S fuel question

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Dave waybright

New member
Hello, I am new to this forum so thanks for letting me in. Last year a bought a boat with a Honda 10HP B100SS/N 1400084 Motor looks really clean and the seller started it up and it seemed to run fine but I'm no expert.

I never ran the motor last season and it was stored in my garage over the winter. I have been trying to get familar with it and I think I may have fuel in my oil.

I put the motor in a barrel of water and when I primed the fuel I found that fuel was coming out of the water check tube. Is that normal? The motor started but the smell of fuel was really strong and the water in the barrel became cloudy. Today I drained the oil and although it was dark, it had a fuel smell that was noticeable and toward the end of the draining I noticed a yellowish streak draining out with the oil.

Should I be concerned about this, and if I need to fix it, how difficult would it be.

Thanks for any information you can share.

Here is a picture.

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Hi Dave and welcome!

I can't think of any way gasoline can enter the cooling passages but we could make a WHOLE NEW WORLD from things I don't know.

There should be a drain tube on the bottom of the carb float chamber and the carb is drained by opening the adjacent valve. Are you sure that valve is closed completely? If the carb is leaking, then the gasoline will drain from the case and into your testing tank.

The most common reason for gas tainted oil in these old motors....
...and it's VERY common indeed....is that the thermost is stuck open.
This results in the engine running much too cold and that results in very poor combustion efficiency. It's actually pretty amazing how quickly an inoperative Tstat can have the oil contaminated with gasoline.

Thermostat is item 7 in link below but you will probably also want to replace item 8 as well as the large gaskets items 2 and 3

Note there are TWO #7's. One is standard temperature and is listed as PRI. The other is for frigid water operation and is labled SUP. Unless you operate in very cold water you will want to install the PRI. Part #
19300-881-741

https://www.boats.net/catalog/honda.../bf100c-la-pre-1997/inlet-manifold-c-d-i-unit


Items 5 and 19 in link below are carburetor drain valve and tube.

https://www.boats.net/catalog/honda...100hp/bf100c-la-pre-1997/carburetor-air-guide

Also...look down the list in these links and you will see there are many parts no longer available. Just pointing it out.

Swapping out the Tstat isn't highly technical but is a pita. That's why many never get serviced.

I hope this helps you and ask all the questions you want. That's why we're all here after all.
 
Wow. I found the valve and it was indeed open! Thanks for that suggestion. I hope this solves that problem. Are you in agreement that the yellow streaking is gas in the oil?

Thanks so much.

jgmo said:
Hi Dave and welcome!

I can't think of any way gasoline can enter the cooling passages but we could make a WHOLE NEW WORLD from things I don't know.

There should be a drain tube on the bottom of the carb float chamber and the carb is drained by opening the adjacent valve. Are you sure that valve is closed completely? If the carb is leaking, then the gasoline will drain from the case and into your testing tank.

The most common reason for gas tainted oil in these old motors....
...and it's VERY common indeed....is that the thermost is stuck open.
This results in the engine running much too cold and that results in very poor combustion efficiency. It's actually pretty amazing how quickly an inoperative Tstat can have the oil contaminated with gasoline.

Thermostat is item 7 in link below but you will probably also want to replace item 8 as well as the large gaskets items 2 and 3

Note there are TWO #7's. One is standard temperature and is listed as PRI. The other is for frigid water operation and is labled SUP. Unless you operate in very cold water you will want to install the PRI. Part #
19300-881-741

https://www.boats.net/catalog/honda.../bf100c-la-pre-1997/inlet-manifold-c-d-i-unit


Items 5 and 19 in link below are carburetor drain valve and tube.

https://www.boats.net/catalog/honda...100hp/bf100c-la-pre-1997/carburetor-air-guide

Also...look down the list in these links and you will see there are many parts no longer available. Just pointing it out.

Swapping out the Tstat isn't highly technical but is a pita. That's why many never get serviced.

I hope this helps you and ask all the questions you want. That's why we're all here after all.
Click to expand...
 
Ok,
Now that you've found the valve...USE IT!
Not yelling at you but emphasing the importance of always making sure your carb is drained anytime you aren't using the outboard.
I don't mean every day but that wouldn't hurt anything.
I mean that, as quickly as gasoline "sours" these days, you should drain the fuel system anytime you won't be using the outboard for 2 weeks or more. Also, burn any unused fuel in the tank in a car or lawnmower or whatever. REMEMBER...STA-BIL will NOT keep today's gas in pristine condition for more than a couple of months in a little outboard tank.

As to the yellow streaks in the oil, yes, I agree that it's PROBABLY gas. But I base that opinion on you saying that you SMELL gas in the oil more than anything else. Whatever the yellow is, it IS contaminate of some sort and doing the oil change was a great idea.

But, the gas odor is why I recommend replacing the thermostat. TheTstat is WAAY more important to the operation and longevity of your outboard (or any other liquid cooled engine) than most people realize.

But on THESE old Honda twins it's even MORE critical!
Because....these outboards don't have a replaceable oil filter. They were built with an oil "strainer" in the sump that you can't get to without removing the power head. As a result, the sump will retain many of the contaminants that enter it in a film of sludge that builds up at the bottom. So...maintenance is really important to keep these babies tip-top. Running the engine dead nutz cold all the time because of a faulty Tstat only adds to the sludgeing process.
 
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