9.9 4-stroke won't idle

Just purchased this 2006 Merc 9.9. Runs great but won't idle - just dies. Took carb apart and cleaned. New hoses throughout, new plugs. But still won't idle. Is their an adjustment for idel?

Re: 9.9 4-stroke won't idle

That is a Tohatsu motor and if you check the Honda/Tohatsu threads you will see lots of posts on idle problems. Most seem to be dirty or clogged carbs. May be time for a 10 micron fuel/water filter if you don't have one. Try running a very strong mixture of SeaFoam mixture with the gas or something like Techron Fuel Injector cleaner. I think the orifices are just too small and get clogged very easy. Honda is just about as bad to.

Re: 9.9 4-stroke won't idle

Mine is a little older, but there should be an idle needle screw on top of the carb (has a black rubber jacket around it). Mine idles best at about 5-6 turns out from bottom, Recomended is 2 1/2 to 5 I believe.

Re: 9.9 4-stroke won't idle

Not my thread but I have the same problem----Thanks, will check that tomorrow-

Re: 9.9 4-stroke won't idle

more than likely, a full carb cleaning is in order, soak it for 4 hours in the bath, minimum. at least that is what the guru's in the tohatsu/nissan section say to do, Paul and Elvin are geniuses, i trust them both with everything on my babies............

a decarb might be a good idea as well, get some sea foam, and do what it says on the can................

going forward, when you are done for the day, UNPLUG the fuel line at the end of the day and let it run out of fuel to clean it out, definitely replace the fuel filter and check all the lines............ replace anything that looks funky, ethanol eats the lines too along with playing h**l with the carbs

if you can, i use VP racing fuel SEL exclusively, because it has NO ethanol in it at all, and has a 94 octane rating, if it is good enough for the fire department and marine rescue around here, it is good enough for me. I learned this from my FIL, he is a FF

Re: 9.9 4-stroke won't idle

Some of those carbs have a series of very fine holes in the topside of the throat that are a real bear to get clean and clear.

I carry a very fine sewing needle in my bag for clearing those holes. Be careful, you do not want to enlarge them, only get the dirt out.

Double check they are clean by spraying a good solvent thru so you can see that each one flows.

Re: 9.9 4-stroke won't idle

The idle cicuit passages can not be cleaned with anything other than chemicals. The holes C.B. speaks of are main fuel feed I think. There are at least 8 threads on this for 9.9/15 4 strokes. Clean the carb with a good soak, be sure to blow out the tiny hole in the top of the ventury on the back side of the throttle butterfly. The Idle screw is behind a brass tamper roof plug that that you can drill with a small drill and pull out carefuly.

Re: 9.9 4-stroke won't idle

I'd tell him how i fixed mine but he ain't been back since he asked :facepalm: