1988 Evinrude120 rough idle

[kryptonite850]

This is probably going to be wordy and I appologize right off the bat, but I have done a bit of troubleshooting and want to include this information so you get an accurate description.

Here goes...

I bought a 1988 Mirrocraft 20ft openbow with an Evinrude 120 (E120TLCCA). I knew it ran with a bit of a miss, so I got the deal I wanted. Now, before replacing the outboard, I want to see if I can get her running right. (I'll just keep the motor on it if I can).

So... what's going on?

Right off the bat, it had a rough idle. I ran it around a local waterhole and when accelerated, it smoothed out. I ran it for about 20 minutes and then it died (thought maybe impeller along with some other idle issue). It was pumping water fine though and the dang thing wouldn't start until I pushed the key in for the choke, then it would start up and idle rough, but start the whole process over again.

I pulled the air cover off and saw that the lower left carb was puking gasoline. It appeared milky. My thought was stuck float and possibly water in the gas. I ordered a rebuild kit for the carb.

I then hooked an external fuel tank to the outboard. This is a clean tank and I put fresh out of the pump gas in it. I pumped out the VRO reserve and put some fresh 2cyl oil in it. I removed the fuel filter and replaced it with a straight through piece.

My carb rebuild kit came! I rebuilt the carb, following the Seloc manual. It quit puking gas! I was happy, but while it smoothed out a bit, it still has a slightly rough idle. It will run great for about 10-15 seconds and then trip over itself for about 10-15 seconds. Then repeat.

I ran a compression check on it and found all 4 cylinders to pump up to 120 and hold fine.

I checked the spark with a basic spark tester (arc style). The spark looked strong and consistent.

I read somewhere that these things will run on 1 cylinder. Probably not smart to do much, but I wanted to find out which cylinder was having issues. I started the motor and pulled each plug wire individually to see what happened. The varying rough idle continued until I pulled the plug wire for the same cylinder that I rebuilt the carb for. When I pulled this wire, it smoothed off pretty good (as smooth as you would expect for running on 3 cylinders), with no more bucking motor.

Found my suspect!

Next, I pulled all the wires off of the plugs and tried each cylinder one by one. It would start on a single cylinder and run briefly on each cylinder, except the one that I rebuilt the carb on. HMMMMM....

I swap the sparkplug with one that was in a good cylinder, no change. I swap the plug wire, no change. I swap the coils, no change. ARGGG... I use the push to choke and that cylinder fires up. Ok, so now is it a weak spark that needs the raw gas or is it not getting fuel?

I unplug all plug wires and crank the engine for a few seconds. I check the plugs and find the problem cylinder to have a damp plug. I wipe it off and wipe off the one above it, then put them back in. I crank the motor a few times and pull the plugs again. Again, a damp plug, but it looks a bit more dry than the one above it. Not much more though.

Back to "maybe I screwed something up in the rebuild, but I really don't think so". The carbs are identical, so as a drastic measure and I HAD to know, I swapped two of the carbs. I really expected the problem to move to the new cylinder for that rebuilt carb. NOPE! Problem stayed in the same cylinder. Eureka! It's electrical! or not...

So I start reading a bit more and come across the reed valves section in the Seloc. Sounds kinda like what is going on. I hold some folded up computer paper infront of each of the carbs and get NO gasoline blowing back through ANY of the carbs. Makes me think that is not the problem. Hmmm... back to electrical, but it's not anything from the coil through the sparkplug.

Any idea what is going on with this motor? Any help would be GREATLY appreciated!

 

[kryptonite850]

Re: 1988 Evinrude120 rough idle

Ok, so I went out after dark and ran the motor (I'm sure the neighbors were cussing me :facepalm to see if I could see any sparks jumping around. I found that there are near constant sparks jumping on the coil for the "bad" cylinder. They jump from the plastic on the coil itself to the mounting bolt (ground). Everything that I've read means that this could be a bad sparkplug, plug wire, or coil. This makes sense to me, but what doesn't make sense is why the problem stayed with the same cylinder when I swapped the coil, plug and plug wire with a known well functioning cylinder's electrical equipment.

 

[kryptonite850]

Re: 1988 Evinrude120 rough idle

Ok, so I went to start it up today with changing NOTHING from last night (I wanted to see if the arc'ing spark was visible in daylight). It ran like crap. Worst I've ever heard it run. Lucky me , the lower right carb was puking gas. Fortunately, I had bought another carb rebuild kit. I pulled that carb and rebuilt it. By now, I'm becoming quite proficient at these and it took no time at all.

I put the carb back on and found no more puking and it is running about like it did last night, so back to the arc'ing spark issue while I wait for two more carb kits to come in by mail. (I might as well finish what I started) and at $20 per kit, I can completely eliminate the carbs as an issue, especially if I end up taking it to a marine mechanic to have him iron out the issues.

In listening to it more today, I realized that it is indeed backfiring with a "pop" when (I'm guessing) that cylinder finally picks up enough juice to fire the fuel.

Oh, and I am ordering new plugs and will be replacing the plug wires soon. Best to eliminate all of that (and hopefully take care of the issues) before I take it to a mechanic and pay out the rear orifice.

I am learning a lot doing this and it has been worth it so far, though it's not fixed.

Anyone see anything that I'm missing here or should I stay the course?

 

[Sureshot]

Re: 1988 Evinrude120 rough idle

I appreciate your updates. I'm facing a similar issue w/ my 50 and I'll be trying that trick for catching arcing by running it in the dark.

 

[kryptonite850]

Re: 1988 Evinrude120 rough idle

Sureshot, I'm looking forward to hearing what you find checking it at dark.

 

[kryptonite850]

Re: 1988 Evinrude120 rough idle

UPDATE:

Here is what I have settled on as being the problems.

Lower right cylinder (looking from the prop side) has an electrical issue, causing the coil to short to ground and only fire occasionally (when hell freezes over, I think). This cylinder will not even attempt to run the engine solo. No sputter, no cough. It's not putting enough fire together to get the ball rolling. More testing showed that it had a very good wet plug (see not firing).

Upper left cylinder (looking from the prop side) needs the carb rebuilt (looking from the prop side). When this cylinder is run with other cylinders, it backfires. Unplug it and the backfire is gone. This cylinder will not run on its own, unlike my two non-problem cylinders (which have the two rebuilt carbs on them incidentally ), who will run the engine solo. It will start but die very shortly (3 seconds or so), probably due to a sticking float causing the bowl to go empty and not refill. It will not restart until a click is heard from that carb (sticky float coming unstuck I suspect).

So, here I am waiting on my rebuild kits and scratching my head, trying to figure out the electrical issue in the lower right cylinder. I tried a brand new plug wire on that cylinder, no luck. I tried a plug swap with one of the good cylinders, no luck (good stayed good, bad cylinder stayed bad). Only thing I can think is it has to be that darn coil, right? I might have to try a coil swap on it again...

I'll post more when I find out more. Feel free to chime in at any time as I will be keeping an eye on this thread.

 

[crb478]

Re: 1988 Evinrude120 rough idle

If you switched coils and the problem cylinder did not move try switching powerpacks to see if the problem changes cylinders , if so replace that powerpack. Check the. Cdi trouble shooting section to diagnois further electrical problems