84 9.9 Johnson runs rich WOT

[CapnChris]

I bought this motor for my 25 foot sailboat and it has had this problem since day 1. Starts great, idles great and runs good until about 1/2 throttle. After that, the bottom cylinder starts missing and blows a tremendous amount of smoke with no power. Here is what I have done so far:
1. Checked compression- 95 psi on both cylinders
2. Replaced power pack
3. Replaced both ignition coils
4. Replaced fuel pump
5. Installed carb kit including float
6. Replaced fuel lines
7. Replaced plugs and wires (gapped to .30)
8. Checked all fuel connectors and fuel line to tank- all ok
9. Removed and inspected intake reeds. Replaced plate and gasket- reeds
ok. (fuel was spitting back into carb- this was corrected)
10. Replaced charge coil

Neither cylinder is misfiring at idle but after running a while, bottom plug is very fouled.
Do I have an internal problem on bottom cylinder even though compression is ok? HELP!

 

[bktheking]

Re: 84 9.9 Johnson runs rich WOT

Is the motor reaching proper operating temperature? Stuck reed caused the lower plug to foul out on mine, found a zip tie stuck in the reed. Basically the one plug it getting too much fuel. What plugs are being used? i'm thinking a reed problem. If your sure ignition isn't a problem of course.

 

[Rick.]

Re: 84 9.9 Johnson runs rich WOT

This motor has cost you a lot of money so far. Sorry to hear that. How do you know it is the bottom cylinder that misfires? Just by the look of the plug? I'm throwing out an idea based on an experience I had with a 9.9 last spring. Bottom cylinder was fouling and every time I checked plug was wet and after a while I realized it had trace amount of water on it as well as fuel. I tightened up all the bolts on the exhaust plate and that solved the water intrusion. Later I had the poser head off it and replaced the gaskets. I haven't experienced it myself but was told by a forum member if the fuel pump diaphram leaks it will allow fuel to be drawn into the bottom cylinder, enough to foul the plug.

I am puzzled that it runs well up to 1/2 throttle, blows excessive smoke (no ignition and no smoke should be generated just lots of fuel in the water) and I wonder if you shouldn't check your compression with the motor up to temperature. Maybe I'm on to something. Could it be your head is leaking water into the lower cylinder but only when the head is up to temperature? These motors run remarkable well on one cylinder. Maybe it doesn't run so good on the lower 1/2 of the throttle either. Maybe your "blows a tremendous amount of smoke" isn't smoke but is water vapor. bktheking knows the inside of these 9.9's far better than I so I'd be interested to hear his take on my thoughts. Maybe he will agree or perhaps challenge some of my thoughts with his own. Quit buying parts until we get this thing figured out. Best of luck. Rick.

 

[CapnChris]

Re: 84 9.9 Johnson runs rich WOT

I also checked the spark -my tester is set at 1/2 inch and I get a yellow spark on both cylinders - about the same intensity.
The reason I suspect the bottom cylinder is the bottom plug becomes very fouled after runnung a while. I still use the motor to get back to my slip after sailing.
'Preciate everyones input.
Chris

 

[CapnChris]

Re: 84 9.9 Johnson runs rich WOT

One more thing- the only time it ran right was after I installed a fuel pump kit. It took off like a scalded dog but I noticed the fuel pump was leaking badly. So I installed a new fuel pump and it was back to its old ways.

 

[bktheking]

Re: 84 9.9 Johnson runs rich WOT

Probably cause the leaking pump was providing just enough gas to get it to go!

 

[jmendoza]

Re: 84 9.9 Johnson runs rich WOT

Aha, saltwater engine guys, he has probably got no thermostat. This is really common, and was the problem I had when I bought my 9.9 Johnson, it had been used by a sailor and they took out the thermostat. This is done because usually the engine does not get flushed, and removing the thermostat prevents it from corroding shut and causing an overheat and subsequent seizure. If the thermo is gone, you will most likely need a new head, I did, why? Because the area where it went, and the thermostat seal seats will be corroded and not seal anymore. I learned long ago to avoid salt water "dinghy" engines, as they have chronic problems from never being flushed.

The other thing is could be is the main jet, or orifice as OMC likes to call it. The ethanol in todays fuel absorbs water and eats away at the brass jets. If the engine is not run dry of fuel and allowed to sit for extended periods, the jets will first turn green, then begin to corrode away and cause uncontrolled rich running.

 

[bktheking]

Re: 84 9.9 Johnson runs rich WOT

And if you need a head, I have one off an 83.

 

[CapnChris]

Re: 84 9.9 Johnson runs rich WOT

The thermostat problem sounds plausible as I have never checked it. It's going to be the latter part of next week before I can get the water cover off so I will keep you posted.
Chris

 

[bktheking]

Re: 84 9.9 Johnson runs rich WOT

Well it would coincide, that's why I asked up a few posts if it was getting up to operating temperature, thermostat issues or blockage.

 

[Rick.]

Re: 84 9.9 Johnson runs rich WOT

I've got my money on a new head gasket right now. Be sure to let us know. The closest my motors have come to salt is when we eat chips in the boat so those issues are hard to imagine. Rick.

 

[bktheking]

Re: 84 9.9 Johnson runs rich WOT

LOL- I second that one- no salt here less tha chips!

 

[CapnChris]

Re: 84 9.9 Johnson runs rich WOT

Problem solved on 84 9.9. As I was running all the fuel out of the motor preparing to tear the motor down, I noticed that right before the fuel in the bowl ran out, the motor started runnning smooth. I installed a valve in the fuel line and sure enough, when the valve was almost closed , the motor would take off like a scalded dog. I knew then that it was a fuel problem. I removed the carb and completely dismantled it. Couldn't really see anything except that the smallertube in the main jet venturi was misaligned with the larger tube. I found a carb on Ebay for 20 bucks, overhauled it and now the old motor runs great now. The new carb turned out to be a 15 horse but works great. Thank you guys for all of your input and I just wanted to follow up to let everyone know the solution to the problem.
Chris

 

[bktheking]

Re: 84 9.9 Johnson runs rich WOT

Great work!