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40hp Johnson missing badly shortly after cranking.

H

huntsman

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My 40 cranks easily idles ok but will not run w.o.t. for more than a minute before missing badly. If I pull EITHER plug wire it will continue to run but worse than with both wires connected. If I turn it off and back on, it runs ok again but shortly after, begins to run rough again. New spark wires, plugs, carb kit last year. New fuel filters and lines. Could this be a sensor problem? ANY help is appreciated.
 
I have been having a similar problem with my 2000 model. I found that I was not getting fuel to both carbs, when I pumped bulb it filled both, but after about 30 seconds the top carb would run dry. I may have fixed it today by replacing the fuel pump. I will not know for sure until I take it to the lake.
 
I think I figured out my problem today, a couple of weeks ago I adjusted my carbs and apparently got both too lean. I read in the manual that the starting adjustment was 2-1/4 out, mine were 1-3/4 out. I went to the manuals recommended starting setting and the problem went away. I guess it wasn't oiling enough and heated up just enough to force it into slow mode.
 
huntsman said:
I guess it wasn't oiling enough and heated up just enough to force it into slow mode.
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NO, that's incorrect. Don't assume such. If it was in SLOW mode, the horn would be blaring, and the hot light on the tach would be lit.

You DO have a Systems Check tach?

It was simply way too lean, and idling badly. Not hot from being lean, not at all.
 
daselbee said:
NO, that's incorrect. Don't assume such. If it was in SLOW mode, the horn would be blaring, and the hot light on the tach would be lit.

You DO have a Systems Check tach?

It was simply way too lean, and idling badly.


Thanks for keeping me straight, I do have the systems check when the engine is first cranked...no tach unless this is what the 4 light check is called???

I have no horns going off or lights on when it slows down off plane and refuses to speed up and go back on plane. If I turn off the key and restart, it runs great for just a few seconds then back to slow speed. After adjusting the carbs, symptom is gone, back to normal.
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Good it's fixed Huntsman....and what you have is the round two - half inch Systems Check gauge with four lights...vertical I think.

The light functions are the same as in the Systems Check tachometer...
 
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