Problem Fixed with pictures!!! Outboard 4 Stroke Engine Problem

[Gobble Doc]

I've got a Yamaha 40 outboard, 1990.  I got it a couple of years ago used and it has run well.  It looks practially brand new.  I put new plugs in it 2 years ago but didn't do it this year.  It has a fuel-water separator and I put a new one in this year.  I have not replaced the fuel filter.  Typically I try to keep the gas fresh.   

Today I was going up the Snohomish and when I was at full throttle it began to loose power.  It never stalled but I was beginning to get concerned.  It seemed to run better at slower speed.  It felt like it just wasn't getting enough gas.  I checked the air valve for the fuel tank and it was open.

My plan is the following:

1.  Get fresh gas.
2.  Replace the plugs.
3.  Replace the fuel filter.

Is there anything else obvious to try?  Or, is it time to look at bigger things like rebuilding the carb? 

What say you experts?  Thanks for any ideas! 

[MADMAX]

One word
Ethanol

take it to the shop
buy pure gas
use Seafoam

[Gobble Doc]

OK.

I usually use the Yamaha Ringfree additive but I can switch to Sea Foam.

If it is an Ethanol problem has it caused a problem that the repair shop can fix?  Or, do you think it sounds like Ethanol issues plus another problem?

Thanks. 

[h2ofowlr]

Pull the fuel hose appart from the bulb to the fuel plug.  Also pull the hose from bulb to tank.  If you have used sea foam, stabil or other fluids it may have broken loose the ethanol that stuck to the ID of the hose and broken loose.  It will look like circular lengths broken into section.  It will plug or allow limited fuel to your engine.  Bulb can be pumped hard, but fuel will trickle out.  Your engine will act like its starving for fuel and cut out.  Also replace fuel filter in engine along with seperator in line.  New tank fuel probably wouldn't hurt.  Make sure you don't have particulate in tank as well.

[Gobble Doc]

h2ofowlr,

Thanks for the ideas.  I did completely empty one of my fuel tanks when I got home and there was some particulate that came out with the last amount of gas.  Not a lot but there was definitely some there. 

[BigGoonTuna]

losing power under throttle sounds like fuel restriction, my guess would be something obstructing one of your carb's main jets(i'm not up on my yami 4 strokes, my 2 stroke 40 has 3 carbs).  it'll run fine at idle and low speed(since the idle jet is clear) but when you open it up it'll start to stumble and lose power.

if your motor has been sitting for any length of time, some crud could have built up, then worked loose.

[steeleywhopper]

I would replace the plugs first, cheap and easy to start with.

[bloodhound]

carbs are the problem 80% of the time from what i see on a day to day basis. 10% will be a failed coil causing no spark on one cylinder which will allow it to run fine but lack power as well, and compression loss can and will cause this as well. you can buy all kinds of things you dont need trying to fix it, but if you do a spark and compression test and you have good spark and good compression on all cylinders its more then likely a carb issue. i have seen blown head gaskets and exhaust port gaskets cause this as well, you have to run the engine for about five min and pull the plugs as soon as you shut it off and see if there is water on the plugs. other then that you can bring it in the shop and pay me and ill fix/troubleshoot it for yah.

[Gobble Doc]

Thanks everyone for your ideas.  I'm going to focus first on the fuel system starting at the gas tank and work my way back to the engine.  I took the plastic tube out of the gas tank today that dips down into the fuel to see if there may be a clogged frit inside the tank but there was no frit to plug.  Next I'm going to look at the quick connect on the tank to make sure it isn't plugged with anything.  Then start looking closely at the fuel line and replace the fuel/water filter.  I also plan to replace the plugs since I've got new ones sitting on my work bench waiting to install.  If none of this easy stuff fixes the problem I'm going to probably have to take a close look at the carb (which is what I think I'll end up doing anyway).  There is also a fuel filter right next to the engine and I found them for $17 so I might as well replace that as well.  Thanks again. 

[Heredoggydoggy]

Probably just a plugged fuel filter.  Gasoline will pass through a filter, and water won't.  Get enough water in the filter=plugged filter.

[lokidog]

Probably just a plugged fuel filter.  Gasoline will pass through a filter, and water won't.  Get enough water in the filter=plugged filter.

Huh?  Water will flow just fine through a filter unless it is designed as a fuel/water seperator.  As mentioned by others, it sounds like you have some flow restriction.  I have a 9.9 that I had to drop the carb because it cut out on me at full speed.  It would then start  and run for only a few seconds.  It has a filter on the end of the fuel take up hose in the tank, and a filter where the fuel flows into the carb, but there was still a bit of silt like material in the carb bowl.  I pulled the jet out of the carb and couldn't see the hole so blew on it and pting, out popped a tiny, tiny bit of something.  If you have more than one carb you may have just one of them plugged, hence the engine runs at low speed. 

I have also had "varnish" in my gas line that had been sitting a while which could have been liquidized fuel hose or stuff actually from the gas, fresh gas would not dissolve it only acetone would touch it.  If your fuel line is older, I would replace it with one that is alcohol resistant, the bulb as well.  A neighbor spent a thousand or so because his fuel line's inner liner had disintegrated and clogged up his fuel injectors.  Spend the extra money for a high quality hose.

Also make sure your air filter, if you have one is clean.

[Gobble Doc]

Thanks for more ideas.

How difficult is it to pull the jet(s) out of a carb?  Do you need some special tool to do this or is it standard sockets, wrenches, etc.?  I've replaced a head gasket in an old mazda truck but I will admit that I'm somewhat intimidated to start taking carburetors apart from of my outboard. 

[lokidog]

Thanks for more ideas.

How difficult is it to pull the jet(s) out of a carb?  Do you need some special tool to do this or is it standard sockets, wrenches, etc.?  I've replaced a head gasket in an old mazda truck but I will admit that I'm somewhat intimidated to start taking carburetors apart from of my outboard.

I did mine sitting on the dock next to the boat with a screwdriver and a socket set, I am not a small engine mechanic but go the job done.  You might bring a jar with some acetone for rinsing metal parts off, I would be careful with gaskets though.  The hard part will probably be getting the carb(s) off the head, though it might be easier on a larger engine than the 9.9 I was working on. 

You could try draining the fuel cups on the carbs first, there should be a drain screw in the side.  If something isw wedged in the jet, this won't help but if it is something that moves into the hole while fuel is flowing and then falls back, it might work.

[Gobble Doc]

Today I removed the small fuel filter by the engine and cleaned it out.  Also washed the filter off with some clean acetone.  There were definitely some particles floating around when I poured the gas out.  Also, there was definite water droplets in the bottom of the container that I emptied the gas into.   

Also got my spark plugs changed and located where I can get no ethanol fuel in town.

Hopefully fresh gas will help out my problems.  If not then I'm going after the carb jets.

[Gobble Doc]

I'm pretty sure I figured out at least a couple reasons my outboard may have had power loss at higher throttle.  First, I took apart my fuel filter and found some water.  Took care of that with no problem.  Also rinsed out the filter with acetone and dried. 

But then I started going through my fuel lines.  At one point I had lines disconnected and I was pumping on the bulb but no fuel was coming out?   WTH?  I spent a half hour going in circles wondering if the check valve in the bulb may be shot...  But then I heard a hissing noise from the fuel/water separator filter.  Hmmm.  I had just put a new filter on that I got today and really cinched it down.  I took it off again and felt where the rubber gasket was supposed to seat.  The edge where the rubber gasket was supposed to seal on the metal rim was completely covered with some kind of inoranic salt.  I took the whole filter assembly off, washed it off with isopropanol, water, and eventually scoured it off with some really fine steel wool until I had a really good surface.  Then dried it all off, inside and out.  Put it all back together, filled up the tank with some ethanol-free gasoline and took it out on the lake for a test.  No more problems!     Maybe I'll find that my carb jets also need help but so far it all looks OK.  Thanks for everyone's help.  Picture 1 and 2 was before and picture 3 was after removing the crud.