Yamaha 9.9 engine trouble - looking for advice

[Max123]

Carb is back together, all cleaned up. Float height was set so that the seam is dead level with the body of the carb by bending the metal tab (you can see this in the background, touching the head of the needle valve). I talked to a tech who said that in the absence of a specific height, this is the best way to go. At dead level, the float is exactly 1" from the rim and is also exactly in line with the set screw for the main jet nozzle - so I think that's right.

I'm also the kind of guy that likes a backup plan. So, I saw an old 9.9 Mariner on craigslist, selling for parts. Turns out, a 1996 Mariner is just a rebadged Yamaha with an identical carb to my 2007, so I picked that up for cheap. Now, I've got a spare carb and can mess around with both. Per ShipHappens, on the older carb, the fuel/air mix screw was uncovered and easier to adjust. I bet the old Mariner ran better than the newer Yamaha. By the time this is all said and done, I hope to have it purring and starting first pull.

Now to wait and try it next time i'm in the Okanagan... Will be a real letdown if it still doesn't run right.

 

[Max123]

Success! (Sort of).

So, brought the rebuilt carb back up to the Okanagan over the long weekend. Float level dialed in, jets 100% clean, enrichment screw cover removed and ready for fine tuning. Backup craigslist carb just in case...

Carb goes on while the engine is still on a stand in the garage and I attempt to get it fired. Absolutely no dice. Coughed/spluttered once, then refused to budge. No trick was getting it started: tape over the intake to simulate choke - nothing. Shot of fuel by juicing the throttle, nothing. Starting fluid direct into the cylinder - nothing.

Finally, after giving up I swap in the craigslist carb.

Aside from designing the world's most finicky carb, I will give Yamaha credit for one thing - this carb is easy to remove. Two 10mm nuts, disconnect the linkage, disconnect a fuel line and a vaccum line and its off.

New carb goes on, starts second pull.

The carb is still acting funky, and I suspect the low speed jet is plugged up. needs throttle to start and revs way up, won't idle below 2000rpm, and needs a good 5 min warm up before attempting to shift into gear or it stalls out. Even then it bogs down when shifting into gear and nearly stalls without a shot of throttle. At first i thought the tach was reading wrong, because it would stall at lower than 2000rpm, but that doesn't appear to be the case. Shifting at 2k is 'crunchy' and not something I like to do. Once in gear and warmed up, it idles along in gear at 1000rpm without complaint but goes back up to 2k when shifted into neutral. Flat out, its a rocket. With just myself and my 10 year old son in the old 12fter we were hitting 5500rpm and 32km/hr. I thik its hitting a limiter because It was going flat out at only 2/3 throttle.

I still couldn't figure out how to set/tune the enrichment screw. The craigslist carb is an older model, and the enrichment screw wasn't sealed so its easy to adjust. When I got it, it was fully tightened down - I experimented with trying to adjust it with the boat in gear - but no real apparent effect. Not entirely sure how it works (is fully tightened down lean?)

Anyway, its back in the garage and on the stand - next time I'll take apart/clean the the idle jet and see if I can get it purring on the stand.

 

[Max123]

For the nerds out there:

This old yamaha runs a 2:08 gear ratio and is swinging a 9.25x9-J prop (Assume this is 9" P). Fairly aggressive prop - large diameter and appears to be the highest pitch listed. At 32km/hr @ 5500rpm I'm at 12.7% slip which isn't bad because these little outboards tend to hang fairly low on the transom and drag a bit in the water.

The guy I got it from was using this motor as a kicker on a 30ft boat... definitely wrong prop for that application - but perfect for bombing around the lake on a little skiff.

 

[submerged]

On my last boat I went through 2 older yamaha 9.9s, and never got either of them to run reliably. Countless hours of frustration and several trips to Garside. These motors do not seem to like light use.

One of the issues I came across was that my fuel tank and hose needed to be replaced. I think it was sucking air, perhaps through a pinhole leak. This was especially annoying as I used the same tank on both kickers, so it might have been responsible for problems with both. The mechanic also told me these motors really don't like old gas. However this being said, I never could get the 2nd motor to run without spraying carb cleaner into the intake to get it going, then keeping it revved up. Didn't make shifting easy. This was after having the carb professionally cleaned.

 

[zurk]

lol. still at it, eh ? i would just do electric drive. the headaches are simply not worth it. the feeling of hitting a button and being propelled along silently is amazing.

 

[Max123]

No - got it running fine - tons of power and generally pretty quiet too. Still playing with the idle a bit.

I've got no complaints for a basically free motor.

 

[Max123]

Still tracking down a low speed idle issue.

After leaving the 9.9 in the garage over the winter, I got it fired up on a stand this saturday to try and get the idle zero'd in. Engine starts up after a half dozen pulls and was able to get a steady idle warm up idle at about 2000rpms. After about 5min I was able to get it the engine to idle down to about 1400rpms (any lower and it would stall). Would shift in/out of gear in a water tank (prop under load), but still not loving the low speed idle. Interestingly, with the engine in gear and the prop pushing water, it will idle at 1000rpm without much complaint.

I know this sounds like an idle jet/carb issue, but I've been through the carb a few times now (rebuilt kit, new accelerator pump diaphragm, cleaned jets, etc). I actually bought a second hand carb to compare, and swap out a few parts to check different jets, check float configuration, etc. I've cleaned the idle jet, and also tried it with both new / old carb. I've also played with the air/fuel mix screw, idle screw, etc. Nothing seems to get me down to a clean, rock solid idle at 900-1000rpm

I was wondering about the fuel pump - this is the one part I haven't touched. Per above, the engine runs fine at speed, its only at idle. How do these fuel pumps work - is it possibly that a partial blockage or fault could cause a low speed fuel pressure issue? Its not an expensive part, so I'm just curious what the symptoms of a failing / partially blocked fuel pump could be.

One other thing. Even when the engine is warmed up, it won't start without a bit of gas. Most engine's I've had will usually startup with no throttle when they are warm, but this one definitely needs the throttle opened up to start.

 

[noluck]

have you ultrasonic cleaned the carb body?

 

[ClintR]

Still tracking down a low speed idle issue.

After leaving the 9.9 in the garage over the winter, I got it fired up on a stand this saturday to try and get the idle zero'd in. Engine starts up after a half dozen pulls and was able to get a steady idle warm up idle at about 2000rpms. After about 5min I was able to get it the engine to idle down to about 1400rpms (any lower and it would stall). Would shift in/out of gear in a water tank (prop under load), but still not loving the low speed idle. Interestingly, with the engine in gear and the prop pushing water, it will idle at 1000rpm without much complaint.

I know this sounds like an idle jet/carb issue, but I've been through the carb a few times now (rebuilt kit, new accelerator pump diaphragm, cleaned jets, etc). I actually bought a second hand carb to compare, and swap out a few parts to check different jets, check float configuration, etc. I've cleaned the idle jet, and also tried it with both new / old carb. I've also played with the air/fuel mix screw, idle screw, etc. Nothing seems to get me down to a clean, rock solid idle at 900-1000rpm

I was wondering about the fuel pump - this is the one part I haven't touched. Per above, the engine runs fine at speed, its only at idle. How do these fuel pumps work - is it possibly that a partial blockage or fault could cause a low speed fuel pressure issue? Its not an expensive part, so I'm just curious what the symptoms of a failing / partially blocked fuel pump could be.

One other thing. Even when the engine is warmed up, it won't start without a bit of gas. Most engine's I've had will usually startup with no throttle when they are warm, but this one definitely needs the throttle opened up to start.

I’ve got no issues with my yami 8hp but I also do need a little throttle to start it. Tiller removed and running 703 controls

 

[Max123]

have you ultrasonic cleaned the carb body?

I didn't, but went through it pretty well (multiple times). All components completely disassembled, including fishing a tiny wire through the jet, and blowing it out with compressed air. Obviously I can't completely rule that out, but I'm try to think of other things that could affect low speed idle stability other than the carb. Like I said, once it is going there is no lack of power or weird behavior.

Its an 18 year old motor, but it wasn't obviously abused of neglected. When I was rebuilding the carb, the only obvious issue was the torn accelerator pump diaphragm and old gaskets. The carb bowl wasn't full of a bunch of ethanol junk . I do suspect that the conversion to ethanol could have messed up some components of the fuel system, and I was thinking that maybe the fuel pump just isn't drawing very well at low idle. But could be something else - spark plugs looked decent, so I'm thinking its not related to ignition.

 

[noluck]

idle circuit is not working properly, there is a blockage somewhere

 

[profisher]

I've had many of these motors and still do. Listen to what you are being told by those in the know. Ship is one of them. Its the idle circuit in the carb. I'm fighting it right now with a carb that I finally gave up on and put my good spare on and **** idle or no start went away and I have a purring kitten again. My problem (my assumption) is that I get it clean and it runs fine for one trip but ethanol has eaten away the factory protective coating on the aluminum inside the float bowl. And it continues to flake away because it has been compromised. So it just re-contaminates itself time and time again. Si I'm looking for another good used float bowl so I can put this back together as a good spare. The picture is of the damage to the coating...the shiny aluminum is what it all looked like just 2 years ago before ethanol in the fuel.

 

[brutus]

For what it’s worth, I don’t even bother cleaning carbs anymore,just toss and put new ones on,( aftermarket Amazon tune up kit) 2 stroke small engines, and four strokes, I know brand name marine carbs are pricy but diking around with them, I’ve never had good success making them run good after cleaning them. Specially after trying a few times it goes right in the garbage

 

[Max123]

Any thought on taking the bowl off and dunking it in an aluminum cleaner like starbrite?

 

[Pineapple Express]

Any thought on taking the bowl off and dunking it in an aluminum cleaner like starbrite?

I've used diluted CLR to clean aluminum carb bits. Don't leave it too long....just 10 mins to scrub and then rinse with water

 

[profisher]

Any thought on taking the bowl off and dunking it in an aluminum cleaner like starbrite?

Soak in a good solvent, rinse and blow out with compressed air. I run a piece of mono fishing line small enough to pass through the tiny drilled passages..the mono is stiff enough to be pushed through, flexible enough to flex around any bends and won't scar the metal. Push in one end until it comes out the other..you know its clear 100%.

 

[kingblazer84]

https://www.amazon.ca/Berryman-0996-Arm-0996-Chem-Dip-Carburetor/dp/B077Y1YSZ5 - its expensive but it works! almost as good as the old not available anymore yamaha carb cleaner solvent