1981 Mercury 25HP Doesn't Start in Cold Damp Weather - Runs great when it does start

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Mar 28, 2015
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I have a 1981 Mercury 25HP which usually starts and runs fine in summer temperatures (around room temperature) but when the temps drop to near or at freezing, it just won't start. I suspect spark problems because sometimes I can get it going by spraying WD40 on the plug wires. In freezing temps that won't even work. I leave the boat floating in the lake all summer with the motor tilted up with the prop out of the water. The engine is usually covered with a poly tarp. Ev IMG_1793.jpg IMG_1794.jpg IMG_1795.jpg en in warmer temps it can take 30-40 pulls to get it going. Later in the day after a run, it will start on one pull practically all the time. I am wondering which components are most affected by moisture and is there a way to determine which component is having the problem by measuring resistance and/or voltage. Does resistance of stator change if moisture is involved? I'm guessing if I had a DVA meter I would notice a voltage drop when moisture is impacting the components? Any recommendations? I presume when it is running well, testing of voltages or resistance will not reveal any problems.
 

racerone

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Dec 28, 2013
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Get or make a simple spark checker.----A proper check for spark forces the system to jump a gap of 3/8" or better.---If it does that moisture is not the problem.----That motor should start with about 3 pulls.---Check your starting procedure.---Check your choke / enricher system to make sure it is working properly.
 
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Mar 28, 2015
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Well, I just got it started after a hundred pulls or so. I can't find my spark checker but laying the plug on it's side on a ground, displayed spark on both plugs. I dropped a little gas mixture down each spark plug hole which made it start firing but then stall. Eventually it fired a few times on each pull, but it took many many pulls before it ran on its own. I suspect now that it runs, it will probably perform well for the rest of the day, until tomorrow morning when I would have to struggle with it all over again.

I can observe a little squirt of gas mixture when I pull out the enricher button. I wish I could figure out what is slowly improves while I pull and pull the thing over until it eventually starts...fuel mixture or spark strength? Or is the block temperature slowly increasing (It is, I can feel it with the odd firing, it slowly warms up.) until the fuel mixture ignites properly? Last fall I took the plugs out and applied heat inside the cylinders with a propane torch but it still wouldn't start. I'll keep looking for my spark plug tester. Will it show the difference between a weak spark and a strong, healthy spark?
 
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racerone

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Testing for ignition with plugs laying on the block is a waste of time !!---Set-up a gap of 3/8" or more for a proper test.
 

oldman570

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The primer bulb should be pumped up till it is hard on a cold startup. The choke should be all the way closed. The motor should fire after a few pulls, less than a dozen. If the motor dose not fire up, the check the primer to see if it is still hard. If the motor dose start, then run it at half choke till it gets warmed up before opening the choke wide open. If the motor still dose not want to start, then you have a fuel supply problem that needs to be repaired. Could be a carb cleaning or rebuild, a new primer bulb, or a air leak in any of the fuel hose connections. If you are using ethanol gas and have not changed the fuel hoses out for ones that are ethanol resisent , they could be a cause of trouble. Always check spark test and compression test before doing work, as it will give a better idea as where to start any repairs. JMO
Oldman570
 
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Mar 28, 2015
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Yes, I would squeeze the primer after every few pulls to check it's firmness, closed the choke until it started, checked the plugs, which seemed quite wet at one point so I gave it a few pulls with teh plugs out. Then it started firing better and eventually started. I appreciate all of the input from everyone.
 

Mi duckdown

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Apr 14, 2007
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manual or enricher choke? Your Pics Mean nothing. serial number? Have both type chokes on different motors. all start up when breaking ice duck hunting. Pics of your carb would help to see what you have.
 
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Mar 28, 2015
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Here's some carb pictures. It has the enricher choke style. I can hear it squirt when I pull out the square black enricher knob. It seems pulling out this knob also changes the timing using a thin metal rod going back under the flywheel. Does anyone have any thoughts why it will gradually start after so many puls? Do you think something gradually dries out as I pull, improving the spark?
 

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Joined
Mar 28, 2015
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Well I took it out for a run late in April. It started fairly easily on that day and ran very well the 4 miles down the lake. The next day after a near 32 degree F night. It would not start at all. after hours of frigging with it, I rowed the boat down to the neighbour's cottage. The old guy there saw that at one point, one plug was wet and the other was dry. He said it might be a compression problem. There was no getting it started at all. I took it to the shop that week and they found that one cylinder had very low compression and it wasn't worth trying to repair.. That seems to be the reason why I had variable performance from it...sometimes running well and sometimes not starting at all. I'll try spraying some oil into the cylinders before trying to start it one day, and I expect it will probably start, since the oil in the cylinders should increase the compression temporarily. I had problems starting a Dodge Colt one time, was advised by a mechanic to dribble some oil down the plug holes and it started right up. Anyway, I bought a used Evinrude 25 HP in May and it starts first pull practically every time, in any weather. What a difference!
 
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