No spark on Merc 85hp

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ryanmul57

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ok i found out my battery wasnt charged and that was why my flywheel was starting to slow so much, but i still cannot get it to turn over. I have attached a video of me trying to. Anything will help thanks!
 
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ryanmul57

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ryanmul57 said:
ok i found out my battery wasnt charged and that was why my flywheel was starting to slow so much, but i still cannot get it to turn over. I have attached a video of me trying to. Anything will help thanks!
Click to expand...
 

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Chris1956

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I could not get the video to play for some reason. If she turns slow with a good battery, the wiring is bad or the starter is bad.
 
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Chris1956

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Those quick disconnect plugs often can be the area of high resistance. For testing purposes, you can wire the battery directly to the starter solenoid and the ground bolt on the lower cowling. Standard battery cables will allow this.

Are the ground straps from the block to the lower cowling good?
 
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Chris1956

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OK, next test is to see if you have spark. You must have +12VDC on the red wire and the adjacent white wire on the switchbox to have spark. If you have spark, spray some 50::1 into the carbs, close the choke shutters and crank her up, cold start lever all the way up. If she doesn't fire, your spark is weak or the timing is off.
 
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ryanmul57

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ok must be a weak spark or timing cause it is sparking and i have the choke closed and still nothing
 
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Chris1956

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If you spray 50::1 fuel into the carbs and she doesn't at least "pop", you have no spark, or the timing is way way off.

A '73 will have timing marks on the upper cowl support. Remove spark plugs and stick a screwdriver in the top spark plug hole. Set that piston to top dead center and look at timing marks and flywheel decal. It should indicate TDC or real close. If not, outer flywheel is incorrectly installed. Remove the six or eight 5/16" bolts and set it to TDC.

Now remove distributor pulley cover and see that cast arrow is pointing to punch mark on flywheel. If not slip belt off and adjust so that it is. Reinstall cover.
Install top spark plug and put timing light on it. Crank motor and read timing. It should be 4-6* BTDC. The brass colored collar (with 2 small stainless steel set screws) control that part of the timing.
 
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ryanmul57

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I believe i did the piston stop method but ill have to check to see if i did it correct or not.
 
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Chris1956

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If she popped with fuel sprayed into the carbs, it sounds like the carbs need some attention.

One more thing. The trigger on your ignition can become intermittent. They can work for some days and then fail, and then work for some more time.

Also, check the spark plug wires for resistance and arc to ground. They screw into the distributor cap. If they are original, they are suspect.
 
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Chris1956

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Well, if the carbs fill, but no fuel will go thru the jets, they are either clogged or do not have adequate air flow thru their throats. The latter would be unusual, if the carb base gaskets are good and the bolts are snug.

If you remove the hex bolts at the base of the bowl, fuel should drip out. That means the mains are clear. or clear enough for now. Next would be to disassemble and clean the idle jet and passages, and rebuild the carbs with gaskets, floats and inlet needle and seats.
 
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