Dropped cylinder

[8ntruck 7,006]

We went to start up the Honda 20hp outboard on our pontoon the other day.  It started and idled well until I went to drop it into gear.  Stalled.  Several tries later I got it going and we started our normal lap around the lake.  A hundred and fifty yards from the dock, one cylinder dropped intermittently.  Headed back to the dock, and the engine stalled as I was approaching the dock.  Fortunately, we had enough momentum to get to the dock.

 

Fresh fuel, non alcohol recreational gas with 2oz per gallon Sea Foam.  The motor (engine?) Is three years old.  Fresh engine oil, filter and lower unit lube.  Pulled the top plug.  Didn't look bad, no wear slightly brown insulator.  No air filter on this.  Fuel lines and priming bulb look good.

 

Once Mrs 8n and the dog got back to the house, I tinkered a bit with the outboard.  Turning the idle speed stop screw a turn resulted in an idle the a would let me shift into gear without stalling.  I drove the boat around a bit and observed that one cylinder would still drop out, then come back, then drop out again.  Throttle setting didn't seem to make a difference.  Performance was definitely off at WOT.

 

We normally take a lap around the lake at a trolling speed, just above idle. Thinking something is 'gunked up', I picked up a new set of plugs and a fuel filter today.  Not sure if that will help, but it certainly will not hurt.

 

Any other ideas?

[JoeM 7,874]

Don't discount an electrical problem. Check / test the coil packs. 

[stevasaurus 22,741]

My Mercury outboard (3 cyl) was doing something like that a few years after I got that engine.  Turned out to be the head gasket and water was running out and shorting out a plug wire.  

[wh500special 2,184]

Does that outboard have a coil/power pack/ignition module/whatever-it’s-called on each cylinder?
 

Same symptoms the old

OMC two cylinders exhibit when a power pack is dying. 
 

steve 

[8ntruck 7,006]

The new set of plugs I installed today solved the cylinder dropping problem. 

 

I did notice that the plug I took out of the bottom cylinder seemed to be wet with oil.  I'm pretty sure if I do a good cleaning on it, I will be able to put it back in the engine without any issue.  

 

Got to wonder where the oil came from.  I typically tilt the motor (engine?) until the lower unit is out of the water when we are not using the boat.  I wonder if that is causing some sort of oil drain back issue.

[wh500special 2,184]

Glad you’re back to running on both cylinders.  
 

I’m just guessing, but I think warm weather and the engine being tilted probably contributes to some oil getting passed the valves when it’s not running.  Both my Honda 90 and Yamaha 8 four strokes will periodically puff a little oil smoke at startup when they’ve been tilted AND it’s been hot and sunny.  The 90 probably has 800 hours, the 8 probably less than 20. 
 

I don’t know if there is anything to it, but many guys on the fishing forums I read preach the need to run the engine hard for a few minutes every once in a while after trolling or puttering around to get the thing hot enough to evaporate gas and water that gets passed the rings and accumulates in the sump.  Might be worth it to open it up and run it like a rental once in a while. 
 

steve

Edited July 1, 2022 by wh500special

[8ntruck 7,006]

Yup.  I try to make a couple of full throttle passes across the lake and back frequently to 'blow the gunk out'.

 

Been poking around in outboard forums.  They say that there is a water separator thingy strapped to the dipstick tube that needs to be emptied from time to time.  I'll give that a try in the near future, too.