9.9 won't hold RPM

[Lady of the Lake]

After starting one of my yamaha 9.9s, I cannot get it to hold at a consistent RPM. It tries to hold and then drops down and eventually stalls. This happens even at high RPMs so it is not just an idle issue. Also, I do not suspect fuel since the other motor idles perfectly. Any thoughts?

Thanks,
Sam

[Allezcat]

Sam; Check for airleaks in the fuel supply (fuel connector, priming bulb, Racor filter, fuel hose) or a fuel supply restriction (engine fuel filter, bad priming bulb, stuck float valve in carb).
Chet
Allezcat

[amytom]

Sam,

If you don't find anything else I would throw a rebuild kit in the carb along with a very thorough cleaning.

Unless...

Does it drop down to less than 2000 rpm quickly then pop back up at times? If so I would also check the oil pressure sensor.


Tom

[Lady of the Lake]

OK, thanks. I have a bulb in the fuel line and was pumping it with no change, still had the issue, so I don't think it is a leak in the fuel lines. I do have a spare carb, I will try that and see if it follow the carb.

[duetto]

sam,

does a 9.9 have the little screw on filter/screen on the port side? if it does, pumping with a bulb doesn't eliminate an air leak there.

[thinwater]

1. Try the small fuel filter on the side first. Easy. A replacement is a few $$ (lawnmower filter) and a few minutes.

2. Fuel pump. Some times they just get weak. Take the discharge hose into a bottle. It should be rather strong, almost like the water discharge on the side of the motor, with some pressure. A 5-minute swap if you have a spare.

3. Dirty carb, specifically the needle valve seat. Take it off, turn it upside down and remove the bowl, and spray it for a while with carb cleaner (make sure to hit the valve seat with the valve up--better, remove the float). you probably don't need the kit, if it's not too old. Just clean it.

Don't be surprised if it is all 3 of these. Because the cause is dirt, it is VERY LIKELY that all 3 are needed. Don't be disappointed. I actually did these 3 steps while underway, single handing, this fall. Not difficult, really. Fortunately the traffic and weather were light.

The engine will also throttle down if the oil is low. Probably not the problem unless the sensor is bad.

[Marc Gershel]

This is a "longshot", but it happened to me. Check the oil level.
I had a leak that I was unaware of. When the oil level gets too low, The engine speed drops back to idle, and when you try to give it more gas , nothing happens. I went crazy with this for almost 2 days, until someone got me to check the oil, and it was empty. I never thought to look, since I had just checked 2 days before. I added oil, and she ran perfectly, for about an hour. Turns out I had a massive oil leak. Luckily I found a good used engine before trying to repair this one. It's a bitch of a job to fix.
Marc

[windrush]

Did you find a solution for yours yet Sam? I'm having exactly the same issue right now. Cleaned out the carb twice... worked for 2 days then the same problem reappeared. I'll replace the filter and try switching the pump off the other engine today as we're in Nassau waiting for the blow to move on. Let me know how you made out.
Bruce

[Page 83]

I found a small collection of "gummy bears" in one carburetor bowl and not the other and still can't understand how that happened. Soaking the carb parts in a gallon can of carb cleaner made it work fine until I replaced both engines.

[Page 83]

As soon as I posted that I remembered: I ran the engines for a while on two separate portable tanks. DOH.