Problem with Yamaha 9.9 4 stroke.

[Rockfish]

Kicker problem with a 1993 9.9 high thrust Yamaha 4 stroke, full remote model.

Kicker starts and idles OK. But produce much less power and thrust than it should at higher rpm. Not really useable except in light current at low speed. Before this occurred the rpm would drop on its own on occasion and then speed up again a little later. It also did this if one stood in the corner/side of the boat with the kicker which is installed on the far outside of a pod. When you stepped over to the other side of the boat it would speed up again. This was fairly recent behavior.

It was service fairly recently with new impeller, plugs and change of oil in the power head and leg etc and ran fine after that.

I am thinking this is most likely a fuel system problem. I am not highly familiar with working on the 9.9 Yamaha but it is like it is fuel starved or has the high speed carb jet clogged or is running on one cylinder. It does sound like something is not normal especially at higher RPM and can stall sometimes if the throttle is returned to low RPM quickly. We have checked the external fuel filter water separator and it is relatively new with no water in it.

My plan is to leave it mounted for now and:

Check the plugs for fouling and to see if one is wet and then replace them.

Replace the motor fuel filter.

Spray carb cleaner down the carb. If it is a clogged high speed carb jet I have no idea what to do or even how to tell if that is the problem.

Check the fuel pump flow and replace the fuel pump if necessary. I may do this anyway.

Check the oil filter and clean/replace.

Check the motor oil level

Check the thermostat with a meter and some hot water on the stove and see if it opens and closes and replace if necessary. If there is salt in there I may replace it anyway.

The manual does not reference an air filter so I don’t even know if it has one?

Is there anything else I should be doing or any advice from those with experience on these motors? If we can’t get it working correctly I guess I will be calling someone who knows what they are doing.

 

[ReelSlim]

Pretty good list of checks there Rockfish. It does sound like a fuel problem like you say. The only suggestion I work make is check your fuel bulb to the kicker and make sure it stays primed all the time and isn't leaking back. I have seen a bad bulb create all sorts of symptoms before.......good luck!

 

[Fish Assassin]

When my motor was surging I took it in under warrenty. I was told all it needed was new plugs. It seems to work. It started doing it again this spring so I replaced the plugs my self. Problem solved once again.

 

[Seafever]

Every once in awhile run alittle bit of fuel injector cleaner (even though it isn't fuel injected).

Also the fuel connector plug to the engine where it clips in can sometimes wear out and start sucking air intermittently which will make engine run erratic. Any air leak in the fuel line anywhere will make it run rough.

 

[Rockfish]

Every once in awhile run alittle bit of fuel injector cleaner (even though it isn't fuel injected).

Also the fuel connector plug to the engine where it clips in can sometimes wear out and start sucking air intermittently which will make engine run erratic. Any air leak in the fuel line anywhere will make it run rough.

I will check over the fuel line and the fuel bulb although I don't think that is the problem. The fuel line is directly plumbed to the motor but I will check for any sign of leaking. I have added two cans of Seafoam but it would have been pretty diluted in the 80 gal fuel tank which the kicker shares with the main engine. The kicker has its own fuel line from the main tank, shut off valve and filter/separator. Come to think of it I will check the fuel cut off lever valve in the bilge to make sure it has not been bumped partially closed.

 

[CIVANO]

Make sure the oil level is not too high. It has a cutout when oil is too high. i had that problem and took forever to figure out and my dealer is the one who changed the oil.

 

[spring time]

can be fuel pump diapram with a bulge in it

 

[Rockfish]

can be fuel pump diapram with a bulge in it

Yes the fuel pump diaphragm is another possibility.

http://www.yamahaoutboardparts.com/forum2/t9-9-fuel-starvation-fixed-long-th3901.html

The more research I do on it the more possibilities come to light. Attached is a link to a forum which speaks to a vapor lock issue with the fuel pump and an upgrade to a newer style fuel pump with internal water cooling. It has occurred to me that if the motor is running hotter because it needs desalting; that it could increase the possibility of fuel pump vapor lock given the older style fuel pump is attached to a cooling block, assuming I have this type??. I may have an even older type which may not be upgradable. We did recently have to do the copper wire bit up the pizzer to get the water discharge running. The boat is moored for the summer and not flushed much so salt build up is a possibility.

I have also been told that spaying carb cleaner down the throat on a four stroke when the motor is running is not a good idea and can damage the motor and that it is better to remove and check/clean/rebuild the carb if necessary - ???

Everything on a boat is always a learning curve. Advice welcome as I have litttle experience with this motor. I am impressed with the simple design, should be easier to work on than most.

Here is the complete Yamaha forum post listings on the site.

http://www.yamahaoutboardparts.com/archive/index.php/f-2.html

Here is a useful link with a lot of good motor diagrams and parts lists. Looks like my motor is a a year newer than I thought; a 1994 T9.9 ELRS.

http://www.boats.net/parts/search/Y...ium=banner&utm_campaign=Yamaha+Outboard Parts

 

[profisher]

Two of the more common problems with these engines both result in gas entering the crankcase and raising the oil level until the engine won't run properly. Crankcase pressure builds and often you will see an oil/fuel sheen on the water in your wake when trolling. Causes are either faulty T-stat resulting in engine never coming up to operating temp or a tear in the fuel pump diaphragm. The latter allows raw fuel directly into the valve cover area then into the crankcase. Oil levels will rise more slowly with a faulty T-stat and can over fill quite quickly with the torn diaphragm.

 

[Hookin'up]

I would pull the carb/s and remove the float bowl/s and check for any sign of crud and also check the jet in the bottom where fuel is sucked up maybe try and run a small piece of strand wire up it or a welding tip cleaner works well sometimes they plug up if left sitting for any extended lengths of time and fuel solidifies.
I also years back had a small 4.5 merc that would run perfect in a barrel and in fact would troll all day long, but when mounted on the boat and under way the second you hit the throttle it would bog and stall would not pull any rpms under load, after many hours in the shop with pretty much a complete OH it turned out to be a bad coil, as soon as it was replaced the problem immediately dissapeared, I still have that motor for my tinny and still runs perfect

 

[profisher]

I wouldn't shove anything up the small orifices in the carb. If it breaks off you have just added to your problems....compressed air is the proper way to clear the small passages. Check your oil level first, if ok then look elsewhere.

 

[pescador]

I just had a similar problem with my almost new 8HP Yam high thrust. Its got low hours and was winterized in Nov but when I started it up this year it didn't run right. Took it into SG and had them put a carb kit in it and new plugs. The key was the carb kit as it seemed to be running lean. Got it back and it runs perfect. Cost was a couple of hundred dollars. If you're using gas with ethonol, it can break down gaskets, plastic parts and works like a cleaning agent. I can't help but think this may be causing some of us problems.

 

[Rockfish]

Two of the more common problems with these engines both result in gas entering the crankcase and raising the oil level until the engine won't run properly. Crankcase pressure builds and often you will see an oil/fuel sheen on the water in your wake when trolling. Causes are either faulty T-stat resulting in engine never coming up to operating temp or a tear in the fuel pump diaphragm. The latter allows raw fuel directly into the valve cover area then into the crankcase. Oil levels will rise more slowly with a faulty T-stat and can over fill quite quickly with the torn diaphragm.

I think you hit on the problem Rollie. Thanks.
We worked on it today and once the motor was warmed up and turned off, we pulled the dip stick and oil/gas pushed up out of the dipstick hole like it was pressurized from heat expansion. We then replaced the fuel filter and the plugs. The plugs looked fouled with black soot/gunk and one seemed a little worse than the other. I think it was just running on one cylinder. Replaced the plugs and the motor started right up and produced full power and a lot of smoke burning up gunk in the combustion chambers. There does not seem to be any problems with spark or fuel supply or the carb in general given the power the motor is now producing. My guess is that gas has leaked into the crankcase and raised the crankcase pressures so much that thined out oil was being pushed up past the rings fouling the plugs. With the new plugs the motor runs fine now although I know it is temporary until the plugs foul again.
Looks like we will be putting the boat on the trailer and replacing the crank case oil, fuel pump diaphragm (cheap) and thermostat (pricy for a simple thermostat). Will look for a tear in the diaphragm. Hopefully that fixes it and its back to fishing or else it’s time to call someone who knows what they are doing.

 

[salmonslayer31]

I had same problem with mine and did all those things and it turned out to be bad fuel.....they are very finicky....

 

[Island Fish Lifter]

I think Profisher is on the right track. Once again, good job bro!

 

[profisher]

Everyone gets lucky once in awhile. I've owned a few of them and the same thing has happened to me 2 or 3 times.

 

[profisher]

The diaphragm may not look torn. ken at SG uses a magnifying glass to look for even a sign of roughness or abrasion which if there will allow gas to seep through. As you say the diaphragm is cheap, replace it regardless while you have it apart. I carry a spare on board when I go out of town. I just put it in my boat as I'm heading to Nootka this week.

 

[sammyslabber]

I would pull the carb/s and remove the float bowl/s and check for any sign of crud and also check the jet in the bottom where fuel is sucked up maybe try and run a small piece of strand wire up it or a welding tip cleaner works well sometimes they plug up if left sitting for any extended lengths of time and fuel solidifies.
I also years back had a small 4.5 merc that would run perfect in a barrel and in fact would troll all day long, but when mounted on the boat and under way the second you hit the throttle it would bog and stall would not pull any rpms under load, after many hours in the shop with pretty much a complete OH it turned out to be a bad coil, as soon as it was replaced the problem immediately dissapeared, I still have that motor for my tinny and still runs perfect

Funny you mentioned crud in the gas seems that it did the same thing to my merc had the carb cleaned twice runs fine now...still seem to find dirt in the bottom of the seperater thinkin the marina drained the last of their tank into mine...sammy

 

[captsteve]

prop

The first thing I thought of when i saw this was The prop. Everything is fine until the boat is under load. Prop could be worn out. Yamaha high thrust props have a feature which keeps them running (turning) unless under load.
I may be way off, but that is immediately what I thought of due to an experience I had.
I looks like your prop is running, but when you really need it under load it does not spin properly. It is very odd if you have not seen it before.

Try checking out your pop or do some research on that problem.
good luck.