Hey Brain,
First step... (make sure it is NOT in gear) .. remove ALL the spark plugs and see if it will pull then..??..You are checking to see if the engine if full of gas..(carb malfunction letting gas run straight through into the cylinders creating hydraulic lock)).. If it does not pull after you remove the spark plugs, you need to proceed to
step two.. put the engine in forward gear and see if you can turn it with the prop..facing the back of the engine, looking to the front of the boat, it should turn clockwise.
Step three .. If the engine will not turn by rotating the prop.. take it out of gear.. trim the engine up and squirt a GOOD shot of PB Blaster around into each cylinder...trim it back down..reinstall the spark plugs..FINGER tight.. you are going to remove them tomorrow....let the "blaster" sit overnight..(We are trying to free stuck rings/pistons..(its usually the rings that stick to the cylinder walls))..
Step four..
NEXT DAY>> remove the spark plugs... see if you can pull the engine over...If the engine will not turn over...
step five . its time to (spray more baster and wait 2 days).will it turn over now??.
.step five...(
IS THIS A TWO stroke or a FOUR stroke),. pull the head off...(no big deal if its a TWO STROKE!).
.a lot more to it if its a FOUR STROKE...( you have the valve train to deal with - requires some skill!!!)
We will proceed as if its a TWO STROKE>>. remove the head...you will be able to see AND FEEL if the pistons are stuck. you should be able to "kinda rock them a tiny bit" inside the cylinders.,if you can't.. they MIGHT be stuck..MORE PB Blaster might work... if you see rust/corrosion/crude around the outside radius of the pistons (where the rings are)..this is not good.. or if you see damage to either of the pistons,,
at this point its probably time for a qualified professional!! Sorry.. Replacing the head will require CLEAN gasket mating surfaces... and a new head gasket,,use the permatex spray for gasket sealer
( NOT SILICON!!!!)
let me know what happens..reply on here. ....please mark as helpful if this helps...
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Shop Mercury Outboard Motor Parts
This is what I use as head gasket sealer on ALL my outboard engines... just spray both sides of the gasket... I have NEVER had a leak..with proper torque sequence.
http://www.oreillyauto.com/site/c/detail/PERN/80064/N2362.oap?ck=Search_N2362_-1_-1&pt=N2362&ppt=C1984
Mercury Outboard Manuals by Seloc 1965 2014
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