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9.9 Mercury will only idle slow, stalls when throttle is opened

B

BigIron

New member
I was out fishing this past weekend and cruising down the lake at almost full throttle when I hit a barely submerged rock reef (apparently known as Prop Island). I manged to push the kill switch and shut off the engine after impact, after gathering my tthoughts as to what just happened I inspected the Prop for damage (Prop was a little dinged up but not too bad) and then started the engine again (it started on the 1st pull), everything seemed OK as I started to open up the throttle and the engine ran fine for about 30 seconds then it started to choke out and stall, I was able to restart the engine again but could only idle at slow speed (it runs perfectly fine at slow idle) as soon as I start to open it up it wants to choke out and stall. I managed to get back to the truck idling at minimum speed.

I'm hoping that someone might have had this problem and can help me out, I would appreciate any input regarding this problem.

Thank you kindly,

Steve
 
Did it kick up violently when you hit? If so, you may have dislodged some crud in the carb bowl that's stuck in a passage somewhere.

Jeff
 
Thanks for the reply fastjeff,

Yes, I would say that I hit the reef at about 2/3 to 3/4 open throttle and the fish finder went flying off the seat and the motor bucked up but did not stall, I actually hit the kill switch on the throttle, had a good look at the prop which had a couple of dings, it looked OK so I dropped the motor back down and it started fine, so I started to open up the throttle again and it went fine for about 20 to 30 seconds than it choked out and stalled. It started again easily (one pull) but from this point on it would idle at slow speed perfectly but would start to choke out and stall as soon as I tried to open up the throttle, so it was a very slow troll back to the truck. The outboard is a 1999 2stroke 9.9 Mercury (I add outboard oil to the gas premixed), it is/was in near new condition only using it a couple times each year. There would be No issue with the Gas being old as the gas was purchased this year and the motor is stored indoors during the winter. There is no grinding noise at all, it idles at slow speed perfectly, other than a couple of dings on the prop everything else looks good.

Steve
 
I think Fastjeff hit it.
If so, you may have dislodged some crud in the carb bowl that's stuck in a passage somewhere.
Click to expand...
Pull the carb apart and blow out the jets and passages. Check the float setting.
 
Thanks for your reply guyjg,

The motor is a year model 2000 9.9 and has not been used that much, maybe 2 times per year, I'm not sure there would be much crud (I'm assumming you mean oil & gas varnishy crud as opposed to something else) in the carb as it looks very clean when look down the carb shaft. I took the motor housing off last night and paid attention to the levers and such as I opened up the throttle and choke mechanism's and everything looked good, the carb intake opened all the way as I throttled full.

Is there a fuel injector cleaner that I could try to run thru the carb or do you mean that the carb has to come completely off and disassembled, cleaned and inspected? I will have to source a Service Manual for this job, mine is a year 2000 - 2 stroke engine and I found a service manual for a year 2000 - 9.9 4 stroke, not sure if this would be an accurate reference. My owners manuals do not tell me much.

Since the motor has been in the garage the last couple of days I did notice that there is a little puddle of what looks to be part gear oil and water, it is a greenish brown color and when rubbed on my fingers it definately has oil in it. I've had a few drops that drip out of the lower shaft before but this was a puddle about the size of a coffee cup lid.

Thank you all for your help,

Steve
 
Is there a fuel injector cleaner that I could try to run thru the carb...
Click to expand...
The only thing I use is Seafoam. You can try. Disconnect the fuel line at the carb and spray a good amount of "Deep Creep" (Seafoam in a can) into the carb using the red extension tube. Disconnect the spark plug and turn engine over several strokes to get the Seafoam throughout the carb. Let it soak overnight. Start the engine; it will smoke alot until the Seafoam is burned which will clean the internals of the engine.


...a little puddle of what looks to be part gear oil and water...
Click to expand...
Pull the prop off and check the shaft seal for oil leaking. Check the shaft for any damage--bent. The waterpump base oil seal may also be leaking.
 
If fuel is left in the carburetors they tend to plug up.-------------You can not see this by " looking " at a carburetor .------------Carburetors must be taken apart for a proper cleaning.-------Always pull fuel line off and let motor run untill carburetor is empty when taking boat out of the water, or if boat is going to sit for a week or more.
 
Sound advice guys, much appreciated!

I will go to Canadian Tire and get the Sea Foam Deep Creep, pull the fuel line off the carb and try to get it as far as I can into the Carb, I'm guessing that I will use just a few squirts and NOT 1/4 or 1/2 or a FULL Can? Let it sit overnight and set up a water barrel (garbage can with water) start it up the next day and hopefully it will throttle up again, failing that I will go to the next step of taking the carb apart and cleaning it with a air compressor and checking the Float settings, which I do not know what I'm doing with this procedure. Any advice would be great.

I will also remove the prop which I have instructions for with my mowners manual and check for damaged shaft and/or seals leaking.

I will make sure I remove the fuel line and run the motor until all fuel is spent in the future as you noted and is also outlined in my manual.

Thanks again,

Steve
 
Check the LU gear oil level before running it. Look for a crack in the gear housing behind the prop. I would use a 10 second spray of Deep Creep or until it backflows out the opening. Turn it over several times and refill the carb w/Deep Creep. Good luck.
 
OK, Neutral with the spark wires off is how it's going be.

I really appreciate everyones time, input and help with this matter, I have family arriving from out of town tomorrow so as soon as I can get a window of time to have a look at the motor I will post my results.

Cheers All ! - Steve
 
Similar problem that Steve has with his 9.9.....please help. I've read this thread and others on the web regarding the Merc 9.9 4 stroke problem with okay slow idle, but stalling when throttle is opened. I recently bought my 2007 version and it starts on first push of the electric start and idles roughly. It consistently stalls when I try to accelerate. I am prepared to rebuild the carb, but need to be able to identify the carb model # and need advice as to where a good place is to order a rebuild kit? Already ordered the service manual from Merc (approx. 2 week wait) and would like to have the rebuild kit here when the manual arrives. Any suggestions?

Thanks, new member,
Andyboy
 
These carburetors are realy quite simple and in most cases ------NO PARTS are needed.-----------------A good study of how they work and a thorough cleaning is what is needed in most cases.
 
racerone said:
These carburetors are realy quite simple and in most cases ------NO PARTS are needed.-----------------A good study of how they work and a thorough cleaning is what is needed in most cases.
Click to expand...

My concern is that a gasket or "O"ring will be damaged during the disassembly. Are there rebuild kits that cover these fragile parts or am I being overly concerned?

Thanks,
Andyboy, '07 9.9 4 stroke Mercury
 
I used the Seafoam on the weekend, with the engine off I opened up the throttle sprayed the Seafoam into the carb housing, let it sit for 5 minutes repeated this about 8 times until the Carb could hold no more fluid. I let this sit overnight as directed and it worked like a charm, my 9.9 mercury purrs like a kitten again and there is no hestitation or stalling problems when the throttle is opened up. I basically filled up a garbage can full of water and kept a hose running all the time while reving the engine.

I had my doubts that it was going to work as the engine is almost brand new (less than 100 hours usage) but it did and I am very grateful for the advise.

Thank you all for taking the time to reply to my post, I really appreciate the advise.

Cheers !

Steve
 
I used the Seafoam on the weekend...sprayed the Seafoam into the carb housing...until the Carb could hold no more fluid. I let this sit overnight as directed and it worked like a charm, my 9.9 mercury purrs like a kitten again and there is no hestitation or stalling problems when the throttle is opened up. I had my doubts that it was going to work as the engine is almost brand new (less than 100 hours usage) but it did and I am very grateful for the advise.
Click to expand...
:eek:
You are welcome. Thank you for your testimonial. Now make sure you add it to the fuel tank when you top off before winterizing and there'll be no plugged idle circuits or jets in the spring. I never run the carbs dry when using Seafoam.

I will state that Seafoam is not a "cure all" and cannot repair a worn out or maladjusted carb or heavy float. But, fuel varnish doesn't stand a chance against it.
 
Thanks again guyjg, I didn't think that my fairly new motor would have any gunk or varnish built up in the carb, but it must have had some and I definately was very surprised when I hit the rock reef going almost full throttle, from 40ft of water to 2 inches and never saw it coming. I'm just glad and alot lucky that I didn't really damage my motor, my prop took a few dings but all and all I'm elated that it turned out to be a minor problem. I do usually add the gas treatment stuff you buy but I never disconnected the gas line and ran the motor till it quit at the end of a fishing trip, I certainl;y will make sure I do from now on. I will also run the motor tonight for a while to make sure all the Seafoam stuff has burnt off before I put it away for the winter.

Cheers !

Steve
 
The rock reef I am referring to is located in the middle near the North end of Crawling Valley Resevoir Alberta, Canada. However, there are many other reefs on this lake as well, I was cruising along in 40 feet of water for quite some time and was just not paying attention to my fish finder as I may have had time to avert the mishap if I seen the depth quickly getting shallower. Big lesson learned as I will be much more careful in the future. I am surprised that some of these reefs are not marked with a bouy of some sort as there are many expensive larger boats that are cruising much faster than what my little 12 foot harborcarft with a 9.9 Merc can do. The next time I go out there I will bring some rope and painted milk jugs or something and mark a few reefs.

Thx - Steve
 
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