Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

[Submariner]

Greetings,

Bought my son a Carolina Skiff J16 with a 2000 Mercury 25M (25HP, 2-Cylinder, 2-Stroke). The motor looks brand new, and I'd be surprised if it had 20 hours on it. Had a full tune-up done before letting my son use it, and it ran flawlessly the first few times we used it.

Taking it to the boat ramp about 4 months ago, I was going through an idle speed zone when out of the blue it started running on one cylinder. Went back to the dock, put it back on the lift, started it the next morning, and it ran perfectly. Took it to the boat ramp, and all was well. Last weekend, the same thing happened. The boat ran perfect the entire day, but dropped a cylinder in an idle speed zone.

I haven't started it since to see if it's back to running normal, but I don't want my son out in the boat with this issue. The engine was gone through top to bottom by an outstanding Mercury mechanic, but it's tough to trouble-shoot because it's intermittent, and you never know when it's going to happen. It sounds electrical to me, so could it possibly be a bad/failing power pack?

Any advice would be most appreciated..

 

[Laddies]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

The 2 things that can cause that engine to drop 1 cyl are the switch box or a coil both are effected by temperature so it's up to you, you can start throwing parts at it which can be expencive or you could buy a OHM meter with a DVA in it or with a plugin DVA the testing is simple and we can give you a test sheet, then you can test the system to find the problem.

 

[Submariner]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

..............you could buy a OHM meter with a DVA in it or with a plugin DVA the testing is simple and we can give you a test sheet, then you can test the system to find the problem.

Thanks very much for the quick, informative response...I have a digital mutimeter, but please pardon my ignorance; what is a DVA?

 

[Laddies]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

A DVA is a direct voltage adapter, it stabilizes peak AC voltage so it's possible to get a correct reading on it. If you don't want to buy one it's simple to make one for about $10 from radio shack parts here's aprint for one.

 

[Submariner]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

Thanks...One thing I'm not very proficient at is electrical items, so is the testing pretty straightforward?

This is a pull-start motor by the way...

On the extreme side, a new power pack and set of coils would cover all the bases?

 

[Laddies]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

The testing is very simple, you might have to get someone to crank if or if it's in the water just let it idle

 

[Submariner]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

Thanks....Where would I find the test procedure? I've built cross-overs, so I can definitely made the DVA....

By the way, could the test be done with the motor running on muffs?

 

[Laddies]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

I will send you the test tomorrow and yes it can be done on muffs but you may have to warm it up by running it under load to make it act up

 

[Laddies]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

 

[Submariner]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

Thanks...Hopefully I can address this in the next week...Does the motor have to be acting up to identify the problem, or will the testing reveal which component is out of spec? Based on the frequency of the issue, I could go for weeks without dropping the cylinder...

 

[Laddies]

Re: Need Assistance with Mercury 25HP 2-Stroke Dropping Cylinder

In most cases of come and go problems it has to be acting up, it's probably a SCR switch in the box but it could be a coil. You might check the ign connections for corrosion