1984 Evinrude 70hp not firing on top cylinder

[jbhasaboat]

I've got an 70hp 1984 Evinrude model E70TLCRD that isn't firing on the top cylinder. If I pull the plug wire on that cylinder there is not change to the motor and if I cover the carb with my hand the motor speeds up instead of choking like the other carbs do. I have tested the spark which is good, checked the fuel lines and replaced a few, replaced the fuel pump , rebuilt the crabs, done a compression check which shows 115 across all cylinders and that top spark plug when I pulled it had oil on it so i'm pretty sure its getting gas. I'm stumped on where to look next so any input would be appreciated!

 

[Daviet]

Re: 1984 Evinrude 70hp not firing on top cylinder

You have spark and compression, seems to have fuel.
Have you swapped the plugs and see if the problem moves to another cylinder, maybe you have a bad plug.
Does the fuel pump pulse line come from that cylinder?

 

[busted-bayliner]

Re: 1984 Evinrude 70hp not firing on top cylinder

if you cover the throat of the carb hence chocking that carb an it speeds up then there is a fuel delivery issue to that carb pull it apart an do a rebuild check all passages also make sure sufficient fuel is getting to that carb through the fuel line

 

[jbhasaboat]

Re: 1984 Evinrude 70hp not firing on top cylinder

I did swap the plugs around and it stays on the top and the pulse line comes from the bottom cylinder. The gas lines are clear and have good flow and I was certain it was the carb so I have rebuilt the carburetor several times meticulously going trough it with a wire through the passages, blowing compressed air through it and soaking it overnight but it changes nothing leaving me scratching my head.

 

[busted-bayliner]

Re: 1984 Evinrude 70hp not firing on top cylinder

I did swap the plugs around and it stays on the top and the pulse line comes from the bottom cylinder. The gas lines are clear and have good flow and I was certain it was the carb so I have rebuilt the carburetor several times meticulously going trough it with a wire through the passages, blowing compressed air through it and soaking it overnight but it changes nothing leaving me scratching my head.

on my 70 the pulse line is from the middle carb was the same on my 65 hp envirude

the main line comes into the middle carb the tees to the other 2 carbs

 

[busted-bayliner]

Re: 1984 Evinrude 70hp not firing on top cylinder

try swapping carbs around see if the problem move with carb

 

[jbhasaboat]

Re: 1984 Evinrude 70hp not firing on top cylinder

The pulse line comes off the intake manifold at the bottom carb. I swapped the carbs around and the problem followed that carb so I borrowed a carb from a friend off his motor that is the same as mine to make sure it was the carb. His was working fine before I put it on my motor it kept doing the same thing it was before then when I took it back he hooked it up to his motor and that carb ran fine again.