Need help. Evinrude 1983 115hp missfiring on one cylinder?

[JCBytes]

This is getting a little bit frustrating.

I'm trying to break in a new rebuild with this Evinrude and it's beginning to behave like a bad omen. Anyway, the motor has been running fine on the hose and in a tank (of sorts) until it was decided to launch and finish breaking her in through a few nice "put-put" rides down the river. Everything was stellar the first night she was in (other than a little bit of weakness in idle) but now I seem to have developed some sort of misfire and cannot go anywhere in gear without it fixed. My question is, once I find out which cylinder isn't firing up, what do I look for and how do I get her fixed?

There is a slight fuel leak in the fuel line where it connects to the motor, but nothing I can't keep on top of for now. Fuel has been run at a 25 to 1 ratio to help with lubrication, but it doesnt' seem to do the spark plugs much good. Upon giving the throttle a few taps by the carbs, I can tell she is building up carbon pretty fast. I can see a few spews of dark smoke clearing out the exhaust when I do that. I'm not trying to tempt fate by giving it a few revs to clear up the smog, because this motor has been running idle long enough in the tank before I launched her. I'm just a little perplexed as to what to expect as the most likely culprit in the misfire situation now. I've done a number of compression checks (without open throttle) and she is giving me around 115psi per cylinder on the nose. COMPLETELY CONSISTENT PRESSURE. I also can see a clear blue spark coming from every spark plug when doing individual checks. No arcing detected at night either. Could this be from bad reeds or something in the carbs? Why would it run so nicely one night and then start breaking down afterward?

Any suggestions would be greatly appreciated. After all of the work I have put into this thing, I am pondering a violent reponse by shooting it with a bazooka or something! At least I could get a little return on entertainment instead of paddling back to shore! LOL.

Thanks in adavnce.

 

[racerone]

The small fuel leak should be fixed "at once " --could be an air leak too.-----------Why was the motor rebuilt and if it was a major mechanical damage was the cause determined ?---------Were carburetors cleaned as part of the overhaul ?-----Have you run with a timing light to pinpoint which cylinder is missing ?------These motors in good condition will idle all day long without " carboning up ", not sure what you mean by " carboning up pretty fast "

 

[JCBytes]

Found the problem and I am sort of surprised to say the least. I have learned a lot since this is my first 2 cycle rebuild job, and I never would have suspected because the manual didn't really stress the importance of the OMC products enough IMHO. Not blaming them really, only my own ignorance. I found that the block halves are leaking air because I didn't use the correct gasket sealer when I reassembled them. The "automotive" type gasket maker in the tube WILL NOT HANDLE the pressure of gasoline AND oil and still bond well enough to sustain a seal. Hind sight is always 20/20 they say... lesson learned. The good news is this hasn't effected my break in of the motor except for a little rough running... other than the fact that I get to spend the rest of my holiday weekend ripping the power head back off and sealing it up correctly. Hope this helps anyone else who's doing a rebuild of their own for the first time. These motors CANNOT run correctly with ANY air leaks period.

 

[JCBytes]

The small fuel leak should be fixed "at once " --could be an air leak too.-----------Why was the motor rebuilt and if it was a major mechanical damage was the cause determined ?---------Were carburetors cleaned as part of the overhaul ?-----Have you run with a timing light to pinpoint which cylinder is missing ?------These motors in good condition will idle all day long without " carboning up ", not sure what you mean by " carboning up pretty fast "

The cause of the dammage was that cyinder 3's needle bearings exploded underneath the piston and made a mess all over. I obtained a new block from a friend which was already honed and ready to use. It's been fun learning how these types of engines function. Thanks for the help racer.

And as for the "carboning up" part, I guess I have been around too many of these motors (growing up) that had a fuel or air leak of some sort which must have caused them to run roughly and blow a lot of smoke if they sat idling for too long in the water. In my ignorance, I believed it was because you have a simple combustion engine with oil mixed in the fuel and that this would naturally foul up a spark plug if it was not run at a high enough rpm with good flow and spark keeping it clean. At least, that was my experience. Silly me.