Re: Mercury 115hp won't start?
I run any gas that is older than 30 days old in my lawnmower and weedeater. The reason I don't keep it past thirty days is because it is almost impossible for me to buy non-ethanol gas in my area. When dealing with ethanol, the gas and alcohol will slowly separate, and the alcohol won't transport fuel oil. Therefore, the engine is running on straight alcohol at times with no lubricant. Not good. #1 source of failure in 2 strokes is no or not enough lubericant. This can also be cause by an excessively lean condition, so carb maintenance on OB motors is also vital. #2 cause of failure is overheating. Since you recently purchased the boat, I would STRONGLY recommend you replace the impeller at a minimum. This also, by process, forces you to drain and replace the lower unit lubricant, which most ppl here agree should be done annually. The isue of the motor smoking while operating could be heat related. Typically, if the correct fuel/oil mixture is being run (which, BTW, is 50:1 for your motor) and there is not a firing problem, these motors smoke very little at optimal running temperatures.
You are on the right track with draining and starting over with fuel. If you can get it, buy straight gas, not ethanol. In TX, stations are required to advertise if they dispense ethanol, not sure if that is federal, or state.
HOWEVER, with a sudden stop issue like yours, on this vintage motor, I would suspect a firing issue of some sort. Previous poster is correct on the procedure. The only thing I would do differently is check compression on all cylinders first. Compression tester is cheap, and if you find a problem, you need to stop and resolve it, or you will quickly acheive total motor failure, which is obviously not good.
My best advice (and you will hear it on here often!) Get the MERCURY service manual for your engine. You can take your serial #, click on the sticky on the front page of the Merc forum at the top that says "What year is my outboard?" and find the year model of your motor. Then search the forum for service manuals, and you will find the Merc part # for your manual. Then, go to Ebay and see if you can't find it, I found mine for $20. If you don't have the patience for that, you can buy it at Amazon (probably $40-60), and if you have even less patience, any Merc service dealer can order it for you, but it will be $80-100. You can do the compression test while you wait on your manual. Compression should be within 10% on all cylinders, you are hoping for a # around 130 psi, but with this age motor, 115 or so is more realistic. 100 or less is low. 80 or less and you have a serious problem. Any deviation of more than 10% is is also a serious problem (it indicates an ongoing carb issue that is damaging one or two cylinders). You can also check for "fire" while you wait. I won't be surprised (and as you do research, neither will you) if you have lost fire to 2 or more cylinders. This indicates a trigger/stator problem, and you will need the manual if you intend to fix it yourself. Another thing to look at while you wait is the condition of the wiring in the motor. This vintage engines were notorious for poor insulation. If you see crumbling, powdered looking, or broken wiring, you can start by fixing it, that may fix your problem.
Welcome to iboats and best of luck to you!
