1975 mercury 850 help

[jeffandtat]

I have no spark at all. Is there an easy test I can do before pulling the flywheel? Also there is a wire that comes from the bottom of the stator that is just hanging there but the weird thing about it is it hasnt been hooked up for awhile and i was running the motor before. Need to know where this double wires home is, it has to go somewhere. HELP THE BARRACUDA ARE GOING OFF. Also carbs need rebuilding is the only way to do this mean to put it in the shop at 85-120 hour.

 

[Scott Rickard]

Re: 1975 mercury 850 help

I just went through a no spark condition on my 1973 Merc 850. Our motors are somewhat similar, but yours may use a different style stator and trigger.

Read this thread for a *general* idea of how to diagnose no spark at the coil or at the sparkplugs:

http://forums.iboats.com/showthread.php?p=2249359

Hopefully someone with a 74-76 850 will come along and give you more specific information.

-Scott

 

[Chris1956]

Re: 1975 mercury 850 help

Jeff, A 1975 Merc 850 has a distributor-based, battery powered ignition. The stator only serves to recharge the battery. Both stator wires should be connected to the rectifier.

That ignition systems must have +12VDC on the red and white wires on the starboard side of the switchbox. The white wire is power from the ign switch to enable the spark. There is a ign test that you can run. it is in the FAQ sections on this forum.

 

[jeffandtat]

Re: 1975 mercury 850 help

thanx for the info i had just about givin up i will try the tests after work tommorow. I will let u know what i found. As for the carb rebuild proberly best to go to the shop ?

 

[jeffandtat]

Re: 1975 mercury 850 help

Cris , well I beleive there is no problem in the harness, because i have 8.3 volts going through at the white and red terminals as per the test. But I think i see a problem the brown terminal on the switch box does not have a wire going to it i checked it anyway at cranking and it was 7.65v. what is difference between dva voltage and dc voltage anyway voltage at the green wire to the coil was 26v. aforementioned brown terminal starboard side

 

[Chris1956]

Re: 1975 mercury 850 help

The brown terminal is unused. It was for the tach signal on early Mercs.
I think 8.3V to the red and white is a bit low, however, Look up the spark test for the distributor based ignition on this forum or the CDI Electronics web page.

The test is: disconnect the elec plug. Remove all three distributor connections from switchbox. jumper white and brown terminals on switchbox together (the ones that went to the distributor). Unscrew coil wire from distributor cap. Reconnect elec plug. Now with ign on, use jumper to ground black terminal on switchbox (the one that used to connect ot the distributor). Every time you ground the black wire, you should get a spark out of the coil (if the coil is good). If so, distributor trigger may be bad, but switchbox, coil, and harness are good.

 

[jeffandtat]

Re: 1975 mercury 850 help

According to the manual all you have to do is pull the flywheel and do your stator switchout. But as the flywheel was coming up I noticed the timing belt was bound up. How do you release that belt and also how does that go back together????????????????