Timing 1985 Mercruiser 120 HP

[lmorefield41]

I'm having trouble finding a post with exactly what I'm looking for. I'm not sure if I have to put this engine into base timing mode. I time it at 8* before, just by hooking the timing light up (without putting it into base timing mode). If possible, is there a manual that shows what the mixture needs to be at? I have them set at 1.5 turns, seems wrong though. Also, is there an idler screw? It's a Rochester 2 bbl Carb.

 

[Don S]

Re: Timing 1985 Mercruiser 120 HP

You have points ignition, no base timing mode. Just set it at idle rpm. by turning the distributor.

 

[lmorefield41]

Re: Timing 1985 Mercruiser 120 HP

Sorry, I forgot to mention that I put electronic ignition on there. Pertronix.

 

[Bondo]

Re: Timing 1985 Mercruiser 120 HP

Sorry, I forgot to mention that I put electronic ignition on there. Pertronix.

Ayuh,.... Same answer...

 

[lmorefield41]

Re: Timing 1985 Mercruiser 120 HP

What about an idler screw and the correct turns for mixture?

You have points ignition, no base timing mode. Just set it at idle rpm. by turning the distributor.

So if I timed it to 8* before TDC, and it's still idling like crap, I should move the distributor until it idles correctly?

 

[Don S]

Re: Timing 1985 Mercruiser 120 HP

You may have to adjust idle speed and idle mixture in order to get the timing set at idle speed.

If you start getting the timing close to where it should be and the engine idles at 400 rpm and dies, then raise the rpm back up to 700 and work on the timing some more.
Once you get the timing right and the rpm right, work on the mixture some, and work back and forth until you get all three working in harmony.

 

[lmorefield41]

Re: Timing 1985 Mercruiser 120 HP

You may have to adjust idle speed and idle mixture in order to get the timing set at idle speed.

If you start getting the timing close to where it should be and the engine idles at 400 rpm and dies, then raise the rpm back up to 700 and work on the timing some more.
Once you get the timing right and the rpm right, work on the mixture some, and work back and forth until you get all three working in harmony.

That's what I figured I had to do, I did this to an extent, and was wondering if there is an idler screw on the carb. I basically just wanted to make sure I'm not going to foul out my spark plugs, or even worse, blow the engine. Thanks for the info.

 

[achris]

Re: Timing 1985 Mercruiser 120 HP

Idle mixture screws will be on the base of the carb, There will be 2 of them, make sure you adjust them the same. Initial setting is 1-1/4 turns out from lightly seated. Get the timing right, then the idle speed, then start playing with the mixtures. Adjust the idle speed as you change the timing and mixtures to keep the engine at 650-700 RPM.

This all assumes the compression is good and the ignition system is healthy.... You'll never get an engine to run right is the compressions aren't good, or the ignition system's not perfect....

Chris........