Outboard Symptoms (help please)

[SVJOCO]

I have a Yamaha 8HP (F8MHA; it’s a four stroke) that for the most part works fine, however it has a few nagging symptoms that I feel may be related.

1) I have to disconnect the fuel hose when I’m not using it, otherwise it becomes basically impossible to start it. I think I’ve figured out that it floods itself somehow. But how?

2) Most of the time I start the engine, I’ll get 5-10 seconds of smoke and then it goes away.

3) As of very recently I’ve lost the ability to plane. It’s like I’ve lost 5% of my power or so.

I changed the spark plugs a couple of months ago. Cleaned the carb 2 weeks ago. I have a Yamaha inline fuel filter/water separator also.

Thoughts on what the underlying issue(s) are?

Thanks in advance.

[rslifkin]

The first issue is likely due to flooding. It's "normal" with a modern un-vented fuel tank that builds pressure. The fix is to add a demand valve into the fuel line from the tank. Since doing that I can leave the fuel line hooked up to my outboard all the time with no issues.

The demand valve uses an outside air reference so it only allows flow when the engine is sucking fuel, but doesn't allow pressure in the tank to push fuel to the engine if the engine isn't sucking.

[Kettlewell]

Many possibilities why you are unable to plane. Often it means the dinghy bottom has become foul. If that is not the case, the carb may be dirty even if recently cleaned. The jets are so tiny on 4-strokes that it only takes the teensiest bit of crud to block or partially block one. I have found that using a good fuel stabilizer, like StaBil 360 or equivalent (the blue stuff) makes a huge difference in keeping your carb running clean too. Your carb could have a sticking float or needle valve too, which can promote flooding and/or mean you're not getting the correct fuel/air mixture. Very common.

[SVJOCO]

Originally Posted by Kettlewell

Many possibilities why you are unable to plane. Often it means the dinghy bottom has become foul. If that is not the case, the carb may be dirty even if recently cleaned. The jets are so tiny on 4-strokes that it only takes the teensiest bit of crud to block or partially block one. I have found that using a good fuel stabilizer, like StaBil 360 or equivalent (the blue stuff) makes a huge difference in keeping your carb running clean too. Your carb could have a sticking float or needle valve too, which can promote flooding and/or mean you're not getting the correct fuel/air mixture. Very common.

So interestingly I was adding Seafoam for most of our trip (months) through the Caribbean but recently stopped thinking I’m probably good for a while. I’ll get back on that train.

When you say needle valve, is that the valve that is attached to the float? If so, you’re the second person to suggest there may be an issue there.

[SVJOCO]

Originally Posted by rslifkin

The first issue is likely due to flooding. It's "normal" with a modern un-vented fuel tank that builds pressure. The fix is to add a demand valve into the fuel line from the tank. Since doing that I can leave the fuel line hooked up to my outboard all the time with no issues.

The demand valve uses an outside air reference so it only allows flow when the engine is sucking fuel, but doesn't allow pressure in the tank to push fuel to the engine if the engine isn't sucking.

I’ve never seen this on someones dinghy before. Is the use of one of these common?

Could you perhaps link me to one of these?

Thanks

[Kettlewell]

So interestingly I was adding Seafoam for most of our trip (months) through the Caribbean but recently stopped thinking I’m probably good for a while. I’ll get back on that train.

When you say needle valve, is that the valve that is attached to the float? If so, you’re the second person to suggest there may be an issue there.

Personally, I think Seafoam is probably snake oil. Practical Sailor has done tests and I think they concluded that Startron and StaBil were the best. I've added StaBil (the blue stuff) to every tank and jug of fuel that goes into multiple outboards, motorcycles, snowblowers, etc. for decades and have not had one carb rebuild in all that time. The needle valve is that little thing that slides up and down as the carburetor float pivots. Sometimes that sticks leading to flooding.

[rslifkin]

Originally Posted by SVJOCO

I’ve never seen this on someones dinghy before. Is the use of one of these common?

Could you perhaps link me to one of these?

Thanks

This is the one I added to our dinghy: https://www.westmarine.com/west-marine-fuel-demand-valve-13854252.html

[GreenWave]

Originally Posted by Kettlewell

Many possibilities why you are unable to plane. Often it means the dinghy bottom has become foul. If that is not the case, the carb may be dirty even if recently cleaned. The jets are so tiny on 4-strokes that it only takes the teensiest bit of crud to block or partially block one. I have found that using a good fuel stabilizer, like StaBil 360 or equivalent (the blue stuff) makes a huge difference in keeping your carb running clean too. Your carb could have a sticking float or needle valve too, which can promote flooding and/or mean you're not getting the correct fuel/air mixture. Very common.

Also if you have a double floor dinghy then it could have some water in it. Ask me how I know. Makes a huge difference.

[Kettlewell]

Here's a link to some Practical Sailor tests of fuel additives. I like and use the StaBil 360.

[SVJOCO]

Originally Posted by Kettlewell

Here's a link to some Practical Sailor tests of fuel additives. I like and use the StaBil 360.

Cool thanks. Check out the YouTube channel “Project Farm” videos on Seafoam.

[SVJOCO]

Originally Posted by GreenWave

Also if you have a double floor dinghy then it could have some water in it. Ask me how I know. Makes a huge difference.

Great thought! But alas, I do not have a double floor.

[SVJOCO]

Originally Posted by rslifkin

This is the one I added to our dinghy: https://www.westmarine.com/west-mari...-13854252.html

Very cool. I’ll definitely add this in the mix when I can. A little difficult to source in Bequia, lol.

[Madehn]

Check your prop for dings or bent blade. Also check your shallow drive bar for proper pitch. Last thing to check is do you have extra stuff that has accumulated doesn’t take much to weigh down a marginal motor boat combo. As for leaving the gas connected try shielding your squeeze bulb from the sun. I suspect this is heating up and forcing fuel into the engine.

[markcouz]

One more vote for flooding via needle and seat, which is causing the starting troubles and smoke.

The needle has a rubber tip that seals against the seat when the bowl is full (pushed up by your float). The smallest imperfection will allow fuel to bypass the seal and flood the engine.

Buy a carb kit for your engine which includes a needle and replace it - it is easy to do.

[KingRichard]

Needle valve/float height - The float is often a separate part from the carb kit, at least in cars. If it's the foam type replace it, if it's brass or a other sealed type and not leaking then it works fine and just check the height.

Also, there is definitely some merit to the modern unvented fuel tank being the original root cause. A check valve or vented tank would help prevent a reoccurrence.

The project farm guy does some neat stuff. My guess, without watching, which I totally will, is he did not find seafoam to be snake oil, but rather some of the applications of it are better than others. Assuming he tested a few. Now that I think of it, you might want to decarbon your engine with it once you have the carb working. Use the process where you choke the engine out with it, wait 15 minutes and then choke yourself out with smoke...