Home › Forum › Ask A Member › 71/2hp evinrude › Re: 71/2hp evinrude
Just want to make sure I am understanding what you posted. The engine ran fine last may, which was the last time you used it…Now, it seems to only run on one cylinder….But, pulling either plug wire off makes little difference in how the engine runs….correct? Well, kind of hard to be sure it is indeed only running on one cylinder based on what you are saying. Usually, if running on just one cylinder, one plug wire removed will make little difference, but the engine will stall if the other wire is pulled….
Are you running the engine on a boat in the water, or in a barrel? Are you pulling the plug wires when the engine is in neutral, or in gear under load?
Why is it that you feel the engine is only running on one cylinder?
These engines have relatively low compression readings, usually higher than 55PSI though, more like 70-80PSI. BUT, compression readings will vary depending on gage used due to the small combustion chambers. Have you tried a different gage? True, the head gasket could be blown between the cylinders causing low readings in both cylinders, but the engine ran OK when you used it last year. Doesn’t seem likely that the head gasket failed while sitting in the garage. True, the cylinders/rings may have gotten rusted while sitting, so it sure couldn’t hurt to soak the cylinders with engine tuner/sea foam.
I’m just hearing some conflicting symptoms, and don’t want you to rip this thing apart needlessly. So, I would direct you back to basics. Try a different compression gage. Are you using fresh fuel/oil mixed at 16:1? Was fuel left in the carb that could have gummed up? Have you tried new spark plugs? You need to do a spark test as well, the spark should be able to jump a 1/4" gap while cranking with the recoil.
Like Casey says, are you sure it is cooling properly? The engine would be low on power if overheating. The only other basic advice I would give is to draing/check/refill the gearcase fluid. Water in the gearcase can cause it to bind, which might lead to a lack of power, poor running….