94 Johnson 9.9 outboard question

[sailboat738]

Hi guys ,

I have a johnson 9.9 on my hunter 23.5 it starts up and runs fine but when im in gear at low revs leaving or coming to the dock it dies. when in open water it runs fine its just at low revs . Any body know how to find the idle screw or has a pdf of the manual ?
any help ?

 

[Kermit]

My mechanic cleaned the carburetor jets when I had the exact same symptoms. Runs like a top at all speeds now including idle.

 

[BrianW]

Kermit's probably got it right. You may first try running a strong gas/Seafoam mixture for a gallon or so. BrianW

 

[Bill Roosa]

check the tank vent if it runs fast for a short time then dies. A vacume created due to a plugged vent will starve the engine of fuel and kill it. To test just take the fuel tank cap off and see if she can operate at high RPM.

 

[BrianW]

Sailboat738, that low speed engine failure is especially worry some as you are coming into a dock a little too "hot" and need that sudden reverse thrust to soften the blow! I've been there, Brother!? BrianW

 

[kloudie1]

dirty low speed jet or jet passage. While tied up at dock, slow it down a lot.. try 1/2 or 3/4 choke to see if that keeps it from dieing.. If it does, it is low speed carb circuit that needs to be cleaned out. Apply the choke slowly and progressively to see if it keeps running.. too much choke will kill t too.
If not, then (in order of complexity) Spark plugs, air leak in fuel lines/connector, Timing (assuming 4 stroke engine?) Valve clearance ..

 

[Benny17441]

Take the carburetor apart and give it a good cleaning.

 

[twodzusfittings]

Possibly look at the fuel hose line. The high ethanol content effects some of the older lines in such a way as to make the interior wall of the hose to swell, causing the inside diameter to shrink. At low speed when the demand of fuel is less, it does not allow the fuel to flow vs. at high speed the suction is greater and allows it to pull through. Try changing out your fuel line and see if that helps. I agree with everyone's suggestions so far, so for sailboat 738, its a matter of process by elimination. Let us know which resolution suggestion is the answer please.

 

[Chris14830]

Hi, If your 9.9 is 1993 to 2001, 2 stroke, then the idle speed adjustment is on the starboard side towards the rear of the engine about 3 or 4 inches from the cooling water tell tale (pisser) tube. The head of the adjustment screw faces rear ward. Its at the lower end of an arm that moves back and forth with throttle. If you take the cowl off and move the throttle it will be pretty obvious.

The idle speed mixture, on the other hand, is on the upper, starboard side of the carb. The head faces out starboard with a spring underneath it. Note with after 1993 carbs the starting point is 4 1/2 turns out, not the usual 1 1/2 turns out. See this great article for reference:
http://www.leeroysramblings.com/OMC_9.9_1993.htm

If your motor is pre 1993 or four stroke, I do not have experience with these.

The comments about carb cleaning, either with additives or diss-assembly are very true, but this adjustment might get you by. AVOID ethanol fuels, the alcohol will suck up water out of the air on cool nights. It will then collect in the float bowl and grow what the mechanics call green snot (technical term?). Your car fuel tank is relatively sealed so its not a problem there compared to a boat.

Good luck.
-Chris

 

[twodzusfittings]

Regarding the idle screw, if this change with lack of idle is happening without having adjusted the idle screw or the fuel/air mixture screw, then I would suggest the issue is elsewhere. If you adjust the screws now and it works better, you have not resolved the issue, just made the mixture more rich, with the end result of using much more fuel and eventually de carbonizing will need to be done sooner along with greater accumulation of carbon. Your exhaust holes in the sleeve will clog up leaving you with another issue. How do I know? Not from my boat motor but my weed wacker. I kept giving it more choke until it would not work anymore. Then, broke down the exhaust and found the holes in the manifold clogged with carbon. After a good cleaning with WD40 and a fine bronze brush, I reassembled and it started up like a champ. So using a can of fog a few times should help. Just my two cents.

 

[celticwinds]

Kloudie has given you the best advise of all the replies. Sounds like the low speed circuit is partially blocked. If you are not familiar with carburetors, leave it alone. You can try locating the jet or jets, carefully screw them in until they stop while counting the turns that it takes so they can be replaced exactly in the same position when you replace them. After they are removed spray some carb cleaner into the openings. Replace the jets exactly the same number of turns that they were in. When screwing the jets in use light pressure. When the screw stops, you stop. Any pressure can damage the jet seats.

 

[sailboat738]

thanks for the reply's
as i said it starts fine runs fine its just moving in and out of the dock at low rpm it cuts out , does any body have a photo of the idle screw ?

 

[John23883]

Mine did the same thing

I thought it was the carburetor, but I had a bad spark plug. It was firing intermittently, so it seemed ok when I checked it, but if I slowed down it would quit running. Replaced it and problem solved. Cheap fix to replace both and worst case you've spent only a couple of bucks.

 

[isaksp00]

On my Honda 8 (4 stroke), with essentially the exact same symptoms (dies when try to idle or put in gear and then throttle up) it has almost always been a dirty idle jet or on occasion other parts of the idle circuit clogging. Usually I just have to remove the idle jet and clean it, but have had to dip (not just spray clean, but dip in real carb dip cleaner) the carb body. Once it turned out that the idle mixture screw was off a bit.