9.9 Johnson cutting out when warm AGAIN ! coil?

[jeffrey9567]

I posted this same problem before. 1976 9.9 Johnson will start cutting out(missing) after running at full throttle for a couple minutes. Everybody seemed to lean toward air leak in fuel system . I replaced bulb, hoses , and clamps. Really thought that was the problem because the bulb never got hard that quick. Still does it though. So when it started doing it I tried cracking the gas cap a little (didn't work). Then tried pumping the bulb ( no good). Played with the lean/rich adjustment both ways (nope). As a crazy last resort I idled down , reached back and took the motor cover off. I then opened it up to full throttle , it sputtered twice and took off like nothing was wrong. What the hell is going on. The outside temp was about 40 degrees. Could one of the coils be malfuctioning when its hot and cooled off when the air hit it.? I'm lost . Ready to use it for an anchor.

 

[kbait]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

Those '74-'76 9.9/15hp's have points. If the armature plate has lateral movement, it will directly change the point gap and cause ignition issues. (I'm assuming you filed-up and re-gapped the pointsets)

If it runs fine w/cowling off, and not when it's on, it could be an exhaust leak choking it out. Not common w/that motor.

Good luck!

 

[rolmops]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

You just posted the solution to your problem. You are not getting proper air to your carburetor.
So either your air holes in the cowling are clogged or you have an exhaust leak that channels exhaust fumes under the cowling and caused a lack of oxygen which will make the engine go very rich and it will start missing until it gets a good supply of fresh air.

 

[jeffrey9567]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

I don't see any holes at all in my cover. Should I put one in ???

 

[kbait]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

Running w/cowling off would be a great test! I'd hook my spark tester up first and scrutinize the spark. Those low-tension magneto's liked to foul plugs if not functioning tip-top w/clean points and a stable platform (armature plate). And then they still may foul a plug..

That said, if you're getting 1/4" consistent blue snappy-spark from each lead, call that good for now (w/new plugs) and test it w/cowling off.

You can read up from an expert here: http://www.sschapterpsa.com/ramblings/OMC/OMC info.htm

 

[rolmops]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

If I remember correctly,the holes are under the handle at the rear of your hood.It's either that or towards the front in your lower cowling.
Don't just put holes in there. The original holes should do the job and if it is exhaust then you have to properly fix that problem.

 

[jeffrey9567]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

What could possible exhaust problems be ? All I know is it comes out from the propeller. I am a novice to boat motors.

 

[rolmops]

Re: 9.9 Johnson cutting out when warm AGAIN ! coil?

If it would all come out from the propeller,there would not be a problem.
Part of the exhaust housing is next to the engine and if there is a bad gasket or a damaged cover over there,exhaust gases will escape into the hood (cowling) where they will build up and get sucked back into the carburetor.