9.9 4 stroke - black soot coming out exhaust?

[Tips Up]

On the weekend my Yamaha 9.9 4 stroke stalled a couple of times which is not normal. The second time was just as we were pulling gear so I did not restart.

I started it up at home and there is black soot coming out the exhaust by prop. I pulled the plugs and they are heavy with carbon. I assume the soot is carbon? Motor is running rich and only used at trolling speed causing a heavy build up?

Any input would be appreciated

Tips

 

[fshnfnatic]

Had a similar problem with my Honda 8 hp 4 stroke last summer.Pulled the carb ,took the float bowl off and gave it a good cleaning,checking the needle and seat as well.Put it back on and it was still producing black soot.I decided to play with the air/fuel mixture screw and removed it making sure how many turns it was to bottom it out so I could return it to its original position.There seemed to be a tiny bit of crud on the pointed end of the screw that I cleaned off.I guess that's all it was because its ran like a top since.It was only a small speck of crap but enough to throw the mixture right
off.I'd give this a try before pulling the carb or taking it to a mechanic.

 

[profisher]

How is the oil level?

 

[Tips Up]

Oil level was first thing I checked. All good. It's not oil its soot. Best I can describe.
It's black and dry feeling. Wants to float.

Thanks FF. I'm not super mechanical so I won't take on the carbs.
I do like to try to figure things out though and fix what I can.

I'm thinking something is making it run rich and it is heavy carbon build up.

Do I just change the plugs and run it up to clear?
Is there a cleaner to run through it?

Or do I just take it in and get the carbs adjusted and mechanic to go over.

Need boat for Saturday so thought I'd start here.

 

[Tips Up]

Thinking harder about it, the throttle on kicker was a bit erratic last couple of trips.
Boat sat quite a bit this winter and I have only been out trolling with kicker a couple of times this year.

In case any of that is a clue.

 

[scott craven]

I would try running a can of seafoam through a tank of gas,
then change your plugs. simple, but quite often it fixes the problem.

 

[Chuck]

I would try running a can of seafoam through a tank of gas,
then change your plugs. simple, but quite often it fixes the problem.

X2. An easy try. Ethanol fuel and sitting is a bad combination.

 

[Derby]

Had the same problem earlier this season... take your carb off and clean your port and needle vales..soak them id sea foam ..and blow them out.. Motor runs like a clock after that

 

[sparkyew]

Had the same problem earlier this season... take your carb off and clean your port and needle vales..soak them id sea foam ..and blow them out.. Motor runs like a clock after that

I had the same issue last season. I have a 2003 yamaha 9.9. I had to drill out the plug on the carb that hides the air/fuel mixture screw and there was crud on the needle and seat. I don't know if this adjustment screw is still hidden on the newer models.

 

[Derby]

I pull 2 valves and soaked the carb in sea foam.. great stuff that sea foam

 

[Tips Up]

Thanks for all of the input.

I'm not confident messing with the carb so I will have to take it in for that.
I won't be able to get it in anywhere until next week.

Meantime I need to be on the water this Saturday so it sounds like I am OK to run it??
The crap coming out worried me so I did not run it long.

I picked up new plugs today. I'll run it up for a bit tonight and see if it blows through.

My main motor and kicker run off the same onboard tank so I'll see if I can get a hold of a small portable tank and run Seafoam through that.

 

[Derby]

U tube it.. its super easy to do... its will take a hr to do..just take your time....

 

[sly_karma]

Even a clean dry 4L milk jug will do at a pinch for a Sea Foam/gas container.

 

[noluck]

if you post up your location, there are alot of members on here with alot of experience that might be able to help if you are close

 

[casper5280]

Just put the Sea Foam in the main tank, it won't hurt the big motor. It's great stuff you can also just spray it into the air intake. As others have said it is a easy job. If you can get the needle values out and blow them out and clean them that is the best way.

 

[Discus]

I cannot answer if it's possible for a carb value needle needs to clean, if not, it's possible for the valve cams need to adjust. if not we need to use the compression test. However, I need to look at it, I will know and answer for the problem.

Because the engine is a 4 stroke.

 

[Tips Up]

Thanks for all the input. I'm in a time pinch this week so I am going to take it in to have carbs looked at next week.
Sounds like it is not serious issue.

Meanwhile I fired it up again last night (now that I know it is OK to run it).
Absolutely no black coming out. LOL.
I changed the plugs and let it run for 20 min. Ran great!

I will still take it in so I can find out why it is running rich and I want to get thermostat checked also.

Tips

 

[Seafever]

One time I had a Chevy truck and the small fuel filter on the carb was replaced at a shop. When the guy did it , he must have dislodged some dirt because when I drove away I got about a mile and it started belching thick black smoke.
Took it back in and there was dirt particles in the float bowl and elsewhere. It was all cleaned out, including needles, and after that no problem.