TOPIC: 1969 Mercury 1250, 125 HP six firing erraticly

This is a friends motor and has just started this problem. Last year I replaced the switch box because of a low speed issue and all was well for the whole year. Now it won't start. When checking the spark on a six cylinder spark tester from Mercury it is getting erratic spark. Kind of all over the place and sometimes not at all. I pulled the distributor cap and all is clean on the inside with no cracks anywhere. Any ideas will be really appreciated.

Best wishes, Carter Powell

You might try pulling the coil wire out of the coil, then unscrewing from the dist. cap. Plug the coil end back in and check for spark coming directly out of the coil.

If you still have erratic spark, it eliminates the distributor cap & rotor as problems. Maybe a problem with the trigger (or ign coil).

If spark is good out of the coil, I'd be taking a hard look at the rotor and cap for arc marks, etc.

The rotor shaft is one assy and quite expensive to replace. The trigger on this ign is also replaceable by itself but is also $$$. I see a couple on eBay around $200, also at marineengine.com for $230.

There's a way to bypass the trigger and check switchbox/coil by themselves.

>Disconnect the (3) distributor wires from the switchbox;
>Jumper together the brown and white trigger terminals on the switchbox;
>Turn ign to "ON" and ground the black trigger terminal on the switchbox. Every time you touch the terminal, you should get a spark. This is replacing the function of the trigger by simulating an opening/closing set of points.

Note that not only should you have constant power on the red-wire-connected terminal on the Starboard side of the switchbox, you should have switched power to the white terminal (Stbd side) any time the ign is in the "ON" or "START" position.

If you have sketchy power to the white wire, it'll cause ign problems. In normal operation, power is killed to the white wire with the ign "OFF".

Anyway, that might get you pointed in the right direction. If the switchbox/coil test still indicates erratic spark, I'd be taking a very close look at the coil for problems. You may have to take the coil out of its mounting bracket to search for arc marks on the coil casing.

HTH..........ed

ED: Thanks for the help, I will let you know how it is going in a couple of days. Thanks so much for the help.

Carter Powell

Welcome over here Carter! Robby from S+F!

I think Ed is right it sounds like a problem with the supply voltage, probably from bad wiring in the harness which is not uncommon. Check that the grounds are solid as well by checking voltage drop tight back to the battery, this will wreak havoc if the system is not grounded well. Disconnect the mercury tilt switch and check for issues with the ignition switch, also a common fault.

Guys: Thanks so much for the information. I WILL get this sorted out in a few days. Hello Robby!

Best wishes, Carter

P.S. Would anyone want to see some pictures of my old school 100mph tunnel boat?

Hi Carter, yeah those pics would be GREATLY appreciated. Pete

Carter Powell wrote:

P.S. Would anyone want to see some pictures of my old school 100mph tunnel boat?

Most Definitely!!!!!

Hell YES!

Pics Please!!!

Hey Guys:

Found the problem. Ed, like you said, check the coil. The coil wire that fits into the coil had a bit of corrosion on the terminal end. Cleaned that off and all is well. Thanks so much for the help. I will get my wife to post those boat pics here in a bit.

Best wishes to all, Carter Powell

Gee, that was easy, may all of your problems be such!!!

Time for fun on the water, and some pics!!!!

Cheers........ed

Can't overlook the little things right Carter! Glad its running good for your friend!