Boat motor will only run on dry land

[uglystick1]

I have an old 40 H.P. Mariner engine that sat for 2 or 3 years without running. I can get it to start with some difficulty when I hook the flushing cups to it in the driveway, but when I put it in the water, it will not start. I checked the compression and it is 140 PSI in both cylinders. I've tested the fuel system from the tank to the carburetor and there are no blockages.I've also tested the fuel pump and it is working as well. The spark plugs are both brand new and properly gapped. I am hesitant to tear apart the carbs unless I'm sure they are the problem. Any ideas?

 

[12Footer]

Re: Boat motor will only run on dry land

To test the carb theory, spray WD40 into the carbs and see if it starts better. If it does, you will need to clean them.<br /><br />I found the cure to this problem on an old merc 35HP to be a plugged exaust port.<br />Check that mud dawbbers haven't made a condominium outta it's exaust. They will sometimes travel way up into the heat exchanging area of the head! <br />But if the engine can't breathe both in and out, it won't run werth a hoot.<br /> I hope they haven't

 

[Rex]

Re: Boat motor will only run on dry land

Let the gas sat in the carbs. for about a<br />week. change gas and use starting fuild to <br />keep it running for a short time.<br />See if that works.

 

[Bob_VT]

Re: Boat motor will only run on dry land

You stated you have checked the fuel system the next would be the electrical. <br /><br />You could also have corrosion on wires and ignition connections. I see you live in an area where salt is used in the winter. When it is in the winter air it plays hell with wires.<br /><br />I would clean all contacts and connections with emery (be sure not to drop particles where they could short things) andd re-tighten everything. <br /><br />Good luck. <br /><br />Bob

 

[fone_man]

Re: Boat motor will only run on dry land

Do not use "starting fluid" to keep it running!!! NO LUBRICATION!!!!!!!!!!! Quick way to engine rebuild/scoring pistons/cyl walls etc.!!!!<br /><br />

 

[TONY H]

Re: Boat motor will only run on dry land

I would bet it IS gummy Carbs.<br />Take some 50 to one gas/oil and put it in a spray bottle, spray some into the carbs as someis cranking it. If it fires up, keep slowly spraying some in to keep it alive. 1 in 100 chance it will clean itself by running but this is an indication that your Jets are clogged. To pull and clean boat carbs aren't as scary as you think. Most of the time the linkage between carbs are preset and can be disconnected without losing it's set.<br />Good Luck