50 HP 2-stroke

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Duke62

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I have a 1985 Mercury 50 hp 2-stroke that will not start. I have replaced the stator, impeller, spark plugs, all fuel lines, fuel filter, and the carbs/fuel pump was rebuilt. The motor started and ran good in the driveway. Took it to the lake, started off the trailer. Went fishing and moved 3 times. On the fourth time the motor would not start and hasn't started since. It turns over and sometimes tries to catch, but will not start. What should I try next?
 
An Evinrude! Lol. Sorry couldn't resist. Is the fuel fresh or old and smelly? Another thing to check is the spark. There are testers but I just use a spare spark plug and look for a hot blue spark not a weak orange one.

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Did you check the basics? Spark, fuel, compression.

Will it run on starting fluid or a prime? If not, no spark or weak spark. If it does, you do not have fuel delivery.

I would put an adjustable gap spark tester and check for spark, it should jump 1/4" or so.
 
First, check compression. It doesn't tell you everything about a motor's condition but it's a good indicator that a motor is worth fixing or not. Best case: I would be pleased if all cylinders are within 10 psi of each other and compression 120psi or better. I could live with at least 100psi compression and all cylinders within15%. Below this, I'll tinker with it but I don't expect much.

Second, verify spark. Spark testers can be had for under $15 at your local auto parts store. If no spark, you have to work your way through the electrical system. There are lots of kinds of ignition systems - you'll need to find the instructions for troubleshooting the one specific to your engine.

Third, verify that you have fuel in the carburetor's fuel bowl. There is probably a screw you can remove on the side of the bowl and you should see fuel pour out. Or, remove the bowl and see if it has fuel in it. This proves that you have fuel at least to the carb, even if it isn't getting through the carb to the engine.

If you have good compression, good spark, and fuel to the carburetors, my next guess is dirty, plugged, or varnished (from evaporated fuel) carbs. I would remove them, disassemble them, clean them, and replace any jets, floats, float needle, seals, or other parts that seem questionable. After rebuilding, find instructions on adjusting the air idle screw on your carb. Usually, you turn it in to gently seat (valve now closed) and turn it out 2 full turns. Hopefully, the engine runs and you turn it in or out until you hit the sweet spot where it sounds the best at idle.

If you can feel air blowing OUT of the carbs in puffs when the motor is turning over - suspect damaged or bent reed valves - this is unusual but it happens.

Lots of other things can go bad but I think this covers the most common issues.
 
Completed compression test 120 all four cylinders. Performed spark test, all four have spark. Bulb is pumping full through the line, fuel is pumping when motor is turned over. Removed carb bowls, plenty of fuel getting to the carbs. Carbs were rebuilt 2 months ago. Gas is only a couple of months old. Tank and all fuel lines are new. Stator, switch box, and plugs replaced two months ago. It makes no sense. I cranked it 5 times in the driveway and let it run random amounts of time the night before I took it out. When I took it out the next moring it stared off the trailer. I fished and moved spots three times. Then on the fourth move it would not start. And has not started since. I can't find anything wrong. It turns over but will not crank.
 
Is the fuel in an onboard tank or a portable? If there is good spark, fuel and compression... I'd be looking closely at that fuel. I've seen fuel come out of ATVs and snowmobiles that wouldn't burn when poured on the door and a lighter held to it.

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Given everything else checks out, I’d wonder if he jets in the carb got plugged.


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Weldorthemagnificent said:
Is the fuel in an onboard tank or a portable? If there is good spark, fuel and compression... I'd be looking closely at that fuel. I've seen fuel come out of ATVs and snowmobiles that wouldn't burn when poured on the door and a lighter held to it.

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Portable tank
 

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