1999 Mercury 90hp crank but no start

Eric123

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Hi, i had just got on the lake yesterday and got about 1/4mile out and the motor just stopped. Got a tow back in and started trying to work this problem out. Well the motor will turn over and over. sometimes with backfire from all the gas its getting. I have pulled the plugs i get fire on the ends of the plugs. i have tried to crank with the lanyard switch off and no fire on plugs/ with lanyard switch on i get fire on plugs. i have cleaned the carbs. got a new bulb on it. checked for cracked or bad fuel lines. and checked the compression. 115lbs. on all 3 cyl. I have read on the internet the compression should be 120-125 for the new motor so im thinking 115 is not bad for mine. But with that compression my motor should be good, right?

Being i figured my compression and motor was ok. i started looking to electrical. The main fuse at top of motor is good. The coil packs are giving fire to the plugs. The plugs are firing. The lanyard switch works. I guess i am needing a little help in other places to check. Would the ignition be causing any problems? Could the voltage from the coil packs not be enough. Or could the plugs still not run the motor if they don't have enough fire?

When i take the plugs out there is gas on the ends of them, but they do fire when i hold it against the motor and turn it over. I am lost on this one and my wife will kill me to spend more money on it. Thanks for all the input u can offer... Eric
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

ok. i have read the "outboard won't start" sticky. i made it down to the check flywheel sheer pin. Can anyone explain checking this in more details or may have a pic? Or anything that i do to check this out?

But as i follow the steps in this sticky it leads me down to this.
 

CharlieB

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Re: 1999 Mercury 90hp crank but no start

Both the flywheel and the crank both have a slot cut into them about 3/16 wide, a steel 'key' is used to keep the two linked. If this key is 'sheared', then the flywheel has spun on the crank, even just a little, and the ignition timing is wrong, causing the motor to fire at the wrong time, the motor cannot run.
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

So. there is only 1 sheer key? And how do i check if it is sheered? Do i remove anything or is there a way to test it?
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

if the sheer key is broke would i be getting compression. I really need a manual for this motor.
 

Silvertip

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Re: 1999 Mercury 90hp crank but no start

Just because the key is sheared does not mean compression is lost. The flywheel and crankshaft need to be liinked in a specific position because the magnets in the flywheel spinning past the stator under it is what sets basic engine timing. You need to remove the flywheel to inspect the key. Even if it is partially sheared, that will affect timing. You will need a special flywheel removal tool to remove the flywheel. They are sometimes available on e-bay. DO NOT PRY ON OR HIT THE FLYWHEEL. Although you may see spark at the plugs, that spark may be weak and not strong enough to actually fire the engine.
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

You will need a special flywheel removal tool to remove the flywheel..

Can i use a automotive puller. i have one that i can pull the top of a briggs and stratton motor with?
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

ok. it was the sheer pin. i went to tractor supply and got "what they called" a woodruff key. When i got back i got it "top dead center" in the top spark plug hole. then put it back together. It cranked then started really good. then i let it run a little (prolly a couple mins) then reved' it up some and it broke the sheer pin again. My question is: Is there a special key that i should use for the sheer pin or will the one from tractor supply be fine? Or is there something else going on that i don't know about? Before it broke the sheer pin it ran really good, better than it did before actually. Is there a website i can get strong sheer pins from? Thanks for all your help

And to be honest. i did rev it pretty good and i did notice that the flywheel came loose a little. Do i need to put that nut back on the flywheel with a airgun? or what is there a certain ft.lbs. of torque that nut needs on top the flywheel or just put on it with airgun?
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

ok. just shooting in the dark here. but when i first pulled the nut off the flywheel all it took was a bump with my wrist on the ratchet to break it loose. i am hoping that it may have been loose enough to sheer the pin in the first place. What do you all think about that? Think my whole problem may have been the previous owner didn't put the flywheel back on to specs? Thanks
 

CharlieB

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Re: 1999 Mercury 90hp crank but no start

The flywheel must fit the taper on the crank almost perfectly or it will not 'seat' fully, and the nut must be tight to keep the flywheel from wobbling or it will soon shear the key again.

You should fine a service manual at one of these links which will have the torque value for the nut.

Ink the crank taper and the key, install the flywheel and nut, then take it apart again and inspect the ink for contact, you should have 90% contact on the taper. Sometimes a key can be just a skoosh to thick and keep the flywheel from setting down fully, you would see the ink smeared off the key into the flywheel slot and little crank taper contact, lightly file the key contacted area, re-ink and refit to retest contact until perfected. This would be the outermost side of the key, not the two parallel sides which index the flywheel to the crank..

http://forums.iboats.com/showthread.php?t=309079&p=2072211#post2072211

http://1manual.com/Mercury manuals/Service_Manual_Index.html
 

Eric123

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Re: 1999 Mercury 90hp crank but no start

hey guys. just a update here. That was my problem. i put a new sheer pin in and set the flywheel nut back to specs. and now she is running fine again. Thanks for all your help and suggestions. I would have probably got ripped a new one at a boat shop for such a simple fix. And im glad it is not motor problems :) Thanks again and im sure i will be around the forums learning more on boats :D Eric
 
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