Engine running on 1 of 2 pistons.

[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.

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.

 

[glassmaster68]

Re: Engine running on 1 of 2 pistons.

compression check that problem cyl,,or both for that matter and see what youve got

 

[kenmyfam]

Re: Engine running on 1 of 2 pistons.

Agree.
Compression check
Spark check (with a spark tester)
Fuel delivery (pump function)
Spark plug condition

Post results and go from there.

 

[usernamesrule]

Re: Engine running on 1 of 2 pistons.

I appreciate the replies guys.

I have checked the plugs I think. I switched plugs with pistons and the bottom runs with either plug. Top never runs. But I did use a little inline spark tester on the top and bottom cylinder. On both, the inline light blinks, which indicates spark is being delivered to the plug.

What's the best way to check the compression? I'd really like to avoid taking it in to a repair shop if I can. Money's a little tight right now, and turn-around times are about 2-3 weeks here in Charleston, SC this time of year.

 

[bktheking]

Re: Engine running on 1 of 2 pistons.

Compression testers-$20 or so at Harbour Freight, Auto Zone etc. Screw it in tight with both plugs out, pull over 5 or so times and read the gauge.

 

[kenmyfam]

Re: Engine running on 1 of 2 pistons.

Grab a decent spark tester while you are there. You need to see a bright blue crackling spark that jumps a 5/8" gap for fun.

 

[usernamesrule]

Re: Engine running on 1 of 2 pistons.

Original Poster again here. I just talked to my dad and he has a compression tester. He's going to bring it over this afternoon and we'll see what that shows us.