Mercury 1250 timing

Biggerstaff · #1 August 27th, 2003, 02:52 PM

I have heard several discussions on what the timing should be set at for the old inlines. Most of what I have found in the forum archives is usually specs from the direct charge outboards and nothing specific to the old crossflows. Could anyone confirm what the specs should be on my 1969 1250ss? And how to static time it?

Thanks

Biggerstaff · #2 August 28th, 2003, 02:59 PM

Biggerstaff · #3 August 29th, 2003, 02:37 PM

corm · #4 August 30th, 2003, 02:18 PM

Hi Big,

The timming is 34 degrees BTDC on that motor. It is best to set it on the water with someone you trust driving, or the safer way. Back the boat in the water till the cavationplate is covered and set the timming with it on the trailier. It will spray water so people may get mad at you. Also watch out so the prop doesn't hit the bottom or the ramp. If your launch ramps are to busy to do it this way you can do this. Pull all the plugs. Put the cyl no. 1 plug in the sparky and ground it to the port side of the motor. Shift the motor into F gear and open the throtal wide open. Turn the key to to on position. Check to see that you have ALL 6 plugs out. Turn the flywheel clockwise by hand while watching the white dot on the top flywheel. As it(or white line on side of flywheel under the dot) comes to the 34deg mark on the decal you will hear & see the spark jump the gap on the sparkplug. When this happens it is where your motor is timed at. It is changed by the spark adv screw on the plate in front of the distributor. If it does not spark at that point you will have to adjust the screw so it does. It is better to have it spark at 32 deg than 36 deg so error on the less advanced side with this motor. The timing decals are set up different on this motor so the 21deg timming that later L6's are set at means nothing with your motor, just in case your wondering about the numbers.

greasemonkeyozi · #5 August 30th, 2003, 03:24 PM

Can this type motor be timed with a standard timing gun and a shop manual?

corm · #6 August 30th, 2003, 08:01 PM

you bet

that is why I like to run them on the water at WOT with a timming light. It is the most accurate way. Either on the trailier or smooth water. One more thing is that you can take an old prop and cut off about 1/3 of each blade to make a test prop which really makes it easy to set your motor up. The motor doesn't jump around then when you set it up on the trailier. One more tid-bit L6 Merc's run full spark advance with about 1/3 butterfly opening the rest of the throtal is fuel related only, so If you don't like the noise you can set it up at a lower RPM. Just make sure that you have FULL spark advance before you change anything.

OOPs I bet you are talking about using the starter to turn the motor over with the plugs out to set the timing at home. Yep you can do that too. *Warning* on this method it is easy to drain the battery down and overheat the starter windings. *Bigger WARNING* it is real easy to run the battery down and wreck this CD type ing. sys. I never use this method myself on this ing. sys.

Footnote; The 125hp Merc is the only Merc that has a mechanical advance that at WOT retards the timing a bit.