engine running on 1 of 2 pistons. Why?

[usernamesrule]

It's a 1997 25 hp Evinrude. It's been running pretty poorly lately. I replaced the plugs(Champion QL77JC4) and the wires(one was bad). Only the bottom piston is working. I know this because I started it yesterday with only the bottom plug connected to the plug wire. The spark plug was in the block, just not connected.

Basically, the engine runs exactly the same whether the top plug is connected or not.

I asked this question last week, and was asked to check the compression. I did that. Both pistons show 110 for compression. That seems to be what it should be, from what I can find on the internet.

Other details: I took out both plugs and turned it over. From the steering wheel(where I turn it over), I can see gas vapor coming out of the top piston, but not the bottom. This seems odd because it is definitely the bottom piston that works. I put a paper towel over both open pistons and turned it over, and it looked like both were ejecting gas onto the paper towel.

Also, I plugged a little inline light into the spark plug wire. It blinks when the plugs are recieving the current. It blinks the both on the same.

I'm not sure what all of this tells me. Seems like both pistons are getting gas and spark. Could the top piston be getting too much gas? I do have to have the throttle up pretty high to make the engine start(on just the bottom cyl).

Thanks for you help guys.

 

[14ftgrumman]

Re: engine running on 1 of 2 pistons. Why?

Use a spark tester to check for spark. You might have good enough spark to have a grounded plug show spark, but sparking under pressure (compression in the cylinder) is another matter. Not familiar with these newer engines, but you should be able to jump a 1/4"gap with a white-blue snap.

 

[Tim Frank]

Re: engine running on 1 of 2 pistons. Why?

When did it last have new plugs?

 

[Rick.]

Re: engine running on 1 of 2 pistons. Why?

I agree you need to check for good spark to see if it will snap across a 1/4 gap. To prove to yourself the top piston is not firing pull the bottom wire while motor is running. If it dies it proves the top is not firing. Rick.

 

[usernamesrule]

Re: engine running on 1 of 2 pistons. Why?

Hi guys. I have new spark plugs in the motor.
I know it's running on only the bottom because it starts and runs the same with the top piston's cable off. I also started it up with both pistons getting spark, and pulled the bottom plug off. It cut off immediately.

I also just swapped the top coil for the bottom coil. That didn't change anything.

So I'm still here with the same problem. Top piston isn't working. I've swapped cables, plugs, and now coils. In any configuration, the bottom piston runs and the top doesn't. I would appreciate any ideas.

When you guys say it should jump a 1/4" gap, how do I test that? The only thing I can figure is that maybe I'm not getting a strong enough spark.

The only spark plug tester I have is a light that plugs in between the spark plug and the cable. it lights up if it's getting current. On both pistons, it lights up.

 

[14ftgrumman]

Re: engine running on 1 of 2 pistons. Why?

You can get a spark tester at almost any AutoZone,Advance
auto or NAPA store.

If there was no change when you swapped coils, the only constant is the plug wire. Change it out with a copper core wire, not the automotive kind, but what you would get if you bought a universal 4 cy. farm tractor wire set.

Give it a try and let us know of your progress.