not firing on one cylinder

[dsteers]

My Evinrude 110 is not firing on one cylinder. I have determined the coil, plug, and wire are good. It is a 1990, with a single power pack. <br /><br />It revs to max RPM out of gear, but won't go past 2500 under load.<br /><br />Should I pull the carb and check the float and jet?<br /><br />Thanks,<br /><br />Doug

 

[Trent]

Re: not firing on one cylinder

If you know the coil and others are good. Its time for a new powerpack.<br /><br />Carb has nothing to do with spark. Did you check for spark at the plug??<br /><br />Also do a compression check.

 

[dsteers]

Re: not firing on one cylinder

Hello Trent,<br /><br />Spark is present on all 4 cylinders. <br /><br />I mentioned the carb and my concerns about its involvement NOT relative to ignition/spark, rather because if the jet was clogged or needle valve were stuck, this would prevent fuel flow to that cylinder, and thus it would not fire. <br /><br />Please explain your thoughts on the power pack; if it is switching current to the coils, what could be failed? Transistor or FET? Voltage breakdown inside the encapsulated assembly? Does the primary voltage to the coil vary as a function of RPM? If so, to what degree?<br /><br />Thanks!<br /><br />Doug

 

[JB]

Re: not firing on one cylinder

Howdy, Dsteers.<br /><br />If you have spark but no power from one cylinder the correct throat of the correct carb is a good suspect.<br /><br />Spray some fuel mix into that throat while running and see if the engine picks up some rpm. If it does, overhaul that carb.<br /><br />If it doesn't make any difference you may have broken a reed or you may have lost compression in that cylinder.<br /><br />Let us know what you find.

 

[dsteers]

Re: not firing on one cylinder

Hello JB,<br /><br />Pardon my French, but I've been screwed. Motor has zero compression on #4. I bought this boat when it was cold and the lake was dowwn, so I couldn't test drive it. Demo'ed it on earmuffs, and sounded fine.<br /><br />Now, no power and won't go above 2500 RPM, except for one 5 minute period where itr went to 5000 RPM and 50+ MPH. So, I neveer gave a thoutht to there being a real mechanical problem. I was looking for little bitty things like ignition and gas. <br /><br />What, if anything, could possible cause intermittent compression loss like this? If it were a 4 stroke I'd look for a sticking valve. But a 2 stroke?<br /><br />Thanks for any additional advice.<br /><br />Doug