Evinrude 8hp black smoke & dead cylinder

[balboa_27]

My junkyard 1991 Evinrude 8hp starts easy and runs smooth, but puts out huge amounts of black smoke and only delivers half power.

It appears to be running on one cylinder, runs the same with the top spark plug disconnected, but not at all with the bottom spark plug disconnected.

The compression is 110 lb in both cylinders, but I haven't tried a leak down test.

The spark itself looks normal. Both new spark plugs are coated with black oil, but appear to be working fine.

I'm running 50:1 TCW-3 oil with Sta-bil.

So far, I've replaced both spark plugs, rebuilt the carb, replaced the reed plate, run a can of Val-tech De-carb through it, and put about 10 lake hours on it.

Any hope, or am I screwed? "Never buy a junkyard engine, unless you are a better mechanic than the guy that scrapped it!"

 

[Daviet]

Re: Evinrude 8hp black smoke & dead cylinder

Spark, compression and fuel, that's all you need. Compression looks ok, did you check spark with a spark tester or by holding the plug next to the block? Spark needs to jump about 3/8" gap and be bright blue.
It may be time to overhaul the carb.

 

[balboa_27]

Re: Evinrude 8hp black smoke & dead cylinder

I used a spark plug tester, and have already rebuilt the carb.

 

[Daviet]

Re: Evinrude 8hp black smoke & dead cylinder

Black oily plugs sounds like a fuel problem. Try squirting some some fuel into the carb when it is running, if it picks up the second cylinder, you still have a fuel problem. If it doesn't , I would suspect the ign system.
About the only other thing I can think of is the upper crank seal, but i would think you would have a lean cylinder if you had a bad seal.

 

[Al-53]

Re: Evinrude 8hp black smoke & dead cylinder

Try swapping the coils around...see if the problem follows to the other cylinder...if so then a coil is needed....

Al

 

[Daviet]

Re: Evinrude 8hp black smoke & dead cylinder

Another thought, is the fuel pump driven off of the top cylinder? Thinking maybe a broken diaphram and leaking fuel into the cylinder.

 

[balboa_27]

Re: Evinrude 8hp black smoke & dead cylinder

Followup question on spark plugs.

Both plugs are new and coated with black oil, but they run fine in the good cylinder. What should they look like?

Since this is a carb engine, the kill switch simply kills the spark while there is still fuel/oil mixture in the cylinders. Won't this always make the plugs oily?