Merc 120 rotation and spark distribution

[Serenity now]

I bought a well used 19' bowrider with a 120 Merc I/O with good compression. <br /><br />It seemed to run fine with the muffs but couldn't get on plane in the water. I decided to check the ignition system, among other things. Assuming that the rotor spins clockwise, I noticed that the firing order was set up as 1-4-3-2, but the tag on the engine reads that it should be 1-4-2-3. Upon closer inspection of the tag, I noticed that it reads "Engine rotation - LH" This completely throws me, since I installed a standard rotation Alpha One and prop and the boat did go forward in forward gear. <br /><br />Does the rotor spin clockwise? Did someone put the wrong tag on this motor?? Thanks for any input..

 

[Haut Medoc]

Re: Merc 120 rotation and spark distribution

I don't know what year you have ...But, I'm pretty sure that the firing order for a 4-cylinder GM is 1-3-4-2. L.H. is a standard rotation engine. The rotor turns clock-wise on all GM engines.....J

 

[Serenity now]

Re: Merc 120 rotation and spark distribution

You're right, it should be 1-3-4-2. I can't believe the motor ran with only two out of four cylinders.

 

[Haut Medoc]

Re: Merc 120 rotation and spark distribution

I guess it could make a difference