1HELP!!! 1971 Mercury 115 has spark but will not crank

[deerhunter2504]

Please help me if possible. We took the boat out on the lake and was running perfect for about 4 hours. Took a break and went to start back up and made a loud backfire noise and has not started since. Wiring was all redone about a year ago so wires are not old. The motor has 115 psi in all 6 cylinders, all spark plugs are firing fine. Usually i can spray a little gas in carb to jump fire it off and that works, but now I can spray gas in carbs and nothing happens. It will sputter like it wants to start but will not crank up. If it is getting spark I do not understand why it will not even fire off. I was told if i am getting spark to plugs this is not an electrical problem. Is this a carb problem? I need help. Please help me. Thanks

 

[Silvertip]

Re: 1HELP!!! 1971 Mercury 115 has spark but will not crank

Timing problem perhaps. Check the flywheel key. The initial backfire may have partially (or fully sheared) the key thus altering the timing.

 

[deerhunter2504]

Re: 1HELP!!! 1971 Mercury 115 has spark but will not crank

Timing problem perhaps. Check the flywheel key. The initial backfire may have partially (or fully sheared) the key thus altering the timing.

I know basics of motor mechanics but getting into timing is out of my field. What is the flywheel key and how to i check if it is sheared?

 

[Chris1956]

Re: 1HELP!!! 1971 Mercury 115 has spark but will not crank

Silver, Do those old Mercs have Woodruff Keys? I thought they were all "W" shaped grindings on the crank and flywheel, like the motors of a few years newer!

 

[crem1]

Re: 1HELP!!! 1971 Mercury 115 has spark but will not crank

Don't rule out carburator cleaning and a new replacement kit and checking the fuel pump would not hurt

 

[emckelvy]

Re: 1HELP!!! 1971 Mercury 115 has spark but will not crank

Silver, Do those old Mercs have Woodruff Keys? I thought they were all "W" shaped grindings on the crank and flywheel, like the motors of a few years newer!

Exactly, there is no key to shear, only one way to install flywheel hub to the crankshaft.

However, it's possible for the belt drive pulley on the flywheel to crack, then it'll shift/move around.

You could tell if this happened by checking belt alignment. You'll have to remove the cover over the distributor pulley in order to check this.

There is an arrow cast into one of the ribs on the pulley; this arrow, when aligned to point exactly at the center of the crankshaft, should also point to the belt alignment marks on the flywheel.

If not, something has slipped. If the belt is not worn out it's likely to be the pulley on the flywheel. Unfortunately you'd have to pull the flywheel to check for that.

You'll need to do a Link 'n Synch when you're done:

http://forums.iboats.com/showthread.php?t=168855

HTH & G'luck with the troubleshooting..........ed