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help with a misfire

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kbcave

Contributing Member
i have a 1985 70hp evinrude 3cylinder motor on my boat. Having a hec of a time trying to fix intermittent missfire. runs between two and three cylinders in the 5mph zone. if you catch it on 3 you can get on a plane and go until it decides to run on two again, it then slows the boat to idle speed.On two you cannot give it throttle very much over idle or it dies. i have got it to run at full speed on and off for a few hrs. Compression is 118 120 110, i have replaced coils, timing base, electronic ignition module, pulled the carbs, no dirt anywhere all flowing through the jets. checked the stator with an ohm meter 1.5 on the yellow wires, .547 on the brown/brown yellow which is from what I can find reading of a good stator. plug wires give a reading of .5 not sure what normal is there. I am completely stuck as of what to try next. any help would be appreciated very much, thanks
 
faztbullet said:
Put a timing light on it and see which cylinder/s are dropping out.
Click to expand...
it is the bottom cylinder, it makes no difference with the plug wire on or off even though the test plug is firing on that cylinder. I put new plugs in before the last test. After coming home and pulling them top two were black, bottom plug was white
 
What fuel pump is on it ?------The fuel pump was not mentioned.----Checked the diaphragm if it is a conventional pump.
 
The fuel pump has no wires or any mechanical device driving it. So I guess it would be conventional. It has two diaphragms and they both appear to be in good condition. I did find a hose at goes to the bottom of the pump with a splint and another running to the pump was off. Neither was fuel supply line but I would guess vacuum. I bought all new lines to run to pump and carb. In response to timeguy I have tried two new sets. So I will go from there. Thanks.
 
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