Cylinder not running

[Mike0704]

I have a 1975 50 hp evinrude top cylinder isn't running. I have gas and fire. Both cylinders have 130 compression. Bottom cylinder runs fine.

 

[racerone]

You need 4 things for motor to run.------Crankcase compression.-----Spark at the right time.----Correct amount of fuel.-----Compression in cylinder.-----How did you determine there is gas at the top cylinder.----Does the spark jump a gap of 3/8" or more ?-----Checked fuel pump diaphragm ?-----Checked reed valves?

 

[Mike0704]

You need 4 things for motor to run.------Crankcase compression.-----Spark at the right time.----Correct amount of fuel.-----Compression in cylinder.-----How did you determine there is gas at the top cylinder.----Does the spark jump a gap of 3/8" or more ?-----Checked fuel pump diaphragm ?-----Checked reed valves?

I can put my hand over the carb and gas will be all over my hand. Reeds are good. I think its a timing issue but not sure wat controlls timing. Fire has good arc

 

[racerone]

Check the flywheel key.-----But timing is fixed at the factory.----And if bottom cylinder runs fine the timing for top cylinder will be ok.

 

[Mike0704]

Check the key its fine. So im think its the coil maybe.

 

[racerone]

??----Post # 3 states ----" fire has good arc" -----So what does that mean ?-----Does spark jump a gap of 3/8" or more , yes or no ?----Swapped sparkplugs ?----Checked / rebuild upper carburetor.----Is there any fuel in the top carburetor ?----High speed jet clean ? ----I will ask again , how did you determine there is gas going into the top cylinder??

 

[Mike0704]

Ok im going to check fire again.im going to change to a better plug ill get back to you on that.i just want to be positive on that. As for the gas to the carburetor i was choking it with my hand.i had both carburetors jet cleaned. Im going to go now and change plug and check the spark

 

[Mike0704]

Ok so spark is jumping a good 3/8. What i did find our is that the cylinders i have fire on upper then it switches. Top cylinder will run but bottom won't then bottom will run and top won't

 

[racerone]

Install new powerpack.-----That may fix it.

 

[Sea Rider]

If spark plugs are in good running condition swap the coils, should work OK on top cylinder and miss, have issues on lower cylinder. If so, one it's shot, better install 2 new ones in, motor will work much better.

Happy Boating​

 

[Mike0704]

Think i will buy new coils but it weird how it swaps cylinders. One works cut it off ,turn it back on and it dont. They are swapping back and forth. They wont both work together.i can start it pull top plug and nothing happens.cut it off turn it back on top is running and bottom is not

 

[Mike0704]

Ok so i found out that both cylinders work but only one at a time. Turn it on only one cylinder will run turn it of an back on the orther runs but the one that was running isn't