1969 Mercury 1250 problem

[Carter Powell]

A friend of mine is having an issue with his motor reving up. It just started this and I thought I would ask to get a starting point on this inline motor. It is not a fuel delivery issue or compression. Battery is good. Idles great just won't rev up. Two years ago this happened and I replaced the switch box and it was fine. Now it is doing the same thing. Could the trigger in the distributor possible cause this.

Many thanks, Carter Powell

[racervboat]

When you give it full throttle does the distributor advance I mean twist ive seen them froze up and not advance or open the carbs up?

[Carter Powell]

I will check.

thanks, Carter

[Carter Powell]

forgot to ask, does the stator on the 1250 have a high speed winding?

Thanks, Carter

[Carter Powell]

Don't know what I was thinking, the stator on the 1250 only generate AC power for the charging system. God I am getting old. Here is what is going on at the lake that motor runs great for about ten to fifteen minutes and then after turning it off for a bit it may or may not take of fine. If it doesn't then it just won't rev up at all. Two years ago it did pretty much the same thing and it turned out to be a bad CD/switch box on this 1969 1250. My friend had another mechanic install another switch box that was supposed to be new in it, it is still doing the same thing. I'm thinking that a broken wire in the coil could be causing this issue as I have seen it on motorcycle coils. Any ideas on this will be greatly appreciated.

Thanks, Carter

[Carter Powell]

The distributor is advancing fully as it should. Any ideas.

Thanks, Carter

[CrayzKirk]

Check the wiring harness on the engine. Mercury's of this vintage are known to have problems with the harness corroding. This includes the stator wiring as well. Check all engine grounds for corrosion. Check the rectifier to be sure that it isn't bad. Check the voltage at the battery while running, it should be over 13vdc. Check the center electrode, cap and rotor inside the distributor. The rotor isn't replaceable so if is bad, you will need to find a replacement. Doesn't sound like the trigger or it would just not run. Switchbox from pretty much any inline 6 from 1967 to 1979 should work just fine. The trigger will be a bit harder to find as it was unique to the 1967 to 1969 motors. I know 950SS, 1000SS, 1100SS, 1250SS and probably some 650SS used them. Perform a link and sync to ensure the distributor primary and second pickup points are correct. The engine should get full advance before the carburetors open very much at all. The 1250 uses a unique advance that actually retards the timing slightly at full throttle.

If all that checks out, make sure the primer bulb isn't being sucked flat and the anti-siphon valve in the fuel tank isn't sticking. As someone else already mentioned, it sounds like the distributor is sticking and opening the carburetors too soon.

Good luck!

Kirk S.

[Carter Powell]

Hello Kirk: Thanks for the reply. I am going to the lake with my friend tomorrow so I can see what this thing is doing on the water. I will let you know what I find out. Thanks so much for the reply. I am darn good when it comes to the V-6 Mercs but it has been a couple hundred years since I spent much time with the old inline sixes.

Best wishes, Carter

[Carter Powell]

It turned out to be a bad coil. Must have had a bit of bad wiring internally. Replaced it with an OLD NEW ONE and it screams. Thanks for all of the information.
Best wishes, Carter