Bottom cylinder won't fire at idle

[Robj]

Hello,

I have a 1994 30 hp Merc outboard, 2 cylinder, with oil injection. It looses the bottom cylinder at idle and surges. If I turn out the mixture screw to about 5 turns, the cylinder fires and the engine runs normal. But I know 5 turn is too much. It sounds like an air leak. I pulled off the reed plate, the valves look OK, the check ball in the check valve for the bottom cylinder disappeared and I replaced it, hoping that was my problem. Put it back together, and still does the same thing. Anyone have any other suggestions? Should I start ripping it apart to look at the bottom crank seal? Or is there something else?

Thanx for your help and have a great day,

Rob.

 

[Robj]

Re: Bottom cylinder won't fire at idle

Anybody?? Suggestions??

Have a great day

Rob.

 

[zorak]

Re: Bottom cylinder won't fire at idle

I was wondering? Do you have the correct spark plugs.I had a merc once that seemed to be doing the same thing.It seemed not to be running on all cylinders and after going thru the ignition wiring and the carbs i put new plugs in it.I had regular plugs that weren't the correct heat range and the right plugs had the flat electrodes.Put them in and it ran perfectly.Something to consider.

 

[JustJason]

Re: Bottom cylinder won't fire at idle

I agree with the plugs. Don't take out what you have and replace them. Take out what you have and look at the book to find the correct plug. 1/2 of all owner maintained motors I see have the wrong plugs. Make sure they are gapped correctly as well.
That being said. Start with the basics.
Compression on 1&2?
Spark as checked via a spark board on 1/2?

You'll need a DVA along with a DMM for this but check the output voltage from the pack to the coil with it running. (NOT from the coil to the plug, that wll hurt you!!!) You want to see anywhere from 100 to 300 volts. Most of them run about 225ish. If you get voltage to the coil shut the motor down and do a resistance check on the coil. Check both the primary and secodary. You may have a bad coil/plug wire. The wires are part of the coil so you just replace the whole thing.
If you are not getting voltage to the coil then you need to check the voltage into the pack from the trigger, and the voltage in from the stator. I believe a 30 is a waste fire spark, It may have a common trigger, so that may not be nessacary.
You can aways swap the leads from the pack (green/white, green/yellow) and see if the problem switches cylinders. If it does then you most likely have a bad coil.

Go to this site...

http://cdielectronics.com/Downloads/tabid/55/language/en-US/Default.aspx

Download the dva charts for mercury as well as the troubleshooting guide and keep it in a binder. Its the holy bible for troubleshooting outboard igniton systems.

 

[Robj]

Re: Bottom cylinder won't fire at idle

Thank you Jason for your reply. Unfortunately I do not believe this is a ignition problem. It is the bottom cylinder not firing due to a lean condition. Since when it gets richened up alot, i.e. 5 turns out of the mixture screw, it will fire. I know there is a strong spark, when I pull the lead to the bottom cylinder, I can see it and unfortunately feel it as well through the gloves. I will try changing the plugs see what that does. I also found another faulty check valve and will replace that. Apparently if the venting systems are plugged, not operating properly, this can lead to this type of problem as well.

My WAG is that it is getting air through the bottom crank seal. How likely is that? Is the sealing set-up on this motor prone to problems?

Have a great day

Rob.

 

[Robj]

Re: Bottom cylinder won't fire at idle

I guess no one has any suggestions to offer. Time to start ripping the piece of junk apart.

Have a great day

Rob.