70hp evinrude cylinder not firing

[Big chief 422]

Any help would be greatly appreciated. I have a 70hp evinrude e70elcnb. Lower cylinder only fires after running motor on full throttle for about ten minutes then it kicks in but will only run for about 5 minutes then sputters out. Ipulled the plug and is black and wet. The other 2 cylinders run fine.I have cleaned the carbs thoroughly. Plugs are sparking good. And the compression is ok

 

[boobie]

Swap the coil with another cylinder and see what happens. If you still have a problem on that cylinder you could have a bad pack.

 

[Big chief 422]

I have swapped the coils. And replaced power pack and still no fire in lower cylinder

 

[Redstern]

The only thing I can think of is maybe the float valve is stuck open in the carb for that cylinder and is causing it to dump fuel in and flood that cylinder.

 

[Big chief 422]

I swaped a carb from one of the running cylinders to the non running one. And still no change

 

[Big chief 422]

The motor has also started to spit a gasy carbon mixture out of the back of the prop

 

[WernerF]

A leaky fuel pump might flood the bottom cylinder. Disconnect the pump's pulse hose. Then pressurize the fuel system with the primer bulb. See if fuel comes out the hose.

 

[Big chief 422]

No fuel came out of pulse hose. I tried new plugs again and after i ran it for a little while i pulled the one from the lower cylinder and it was dry, no gas wasnt blackend, look brand new

 

[boobie]

Will the spark jump a 7/16 " open air gap on a tester when running ??

 

[Big chief 422]

I ran another compression check today and that bottom cylinder is reading 0

 

[Big chief 422]

Found my issue. I pulled the cylinder head and it is all chewed up. Is it worth trying to fix or should i start looking for a new motor

 

[boobie]

You said in post #1 your compression was okay !! Oh,Well !!