Rich Condition at idle
 

I did some mods on my 502 EFI engines and by putting an external adjustable regulator on and increasing the pressure to 42# the motors run good at mid and full throttle. But at idle they run real rich now. Is there any way to get this out, maybe by adjusting the screw on the throttle plate. I was wondering if this would let more air in at idle??

Opening the air valve will only make the computer close down the Idle Air Control Valve and retard the timing. Are you sure the fuel pressure drops at idle from the fuel pressure regulator. High intake manifold vacuum (at idle) should pull against the diaphragm and drop the fuel pressure. Check it out.
Dennis Moore

After changing my stock exhaust for Gils', and my flame arrestor, I noticed my plug readings were a little lean. So, I did as you did, I added an adjustable regulator. This solved my lean problem but created a rich condition at idle just like yours. I added an MSD6M-2 to the stock ignition. This helped my rich condition at idle and cleaned up the dirty transom. BUT, don't expect any top speed increase. I saw no change at all with the MSD.

The fuel pressure does drop at idle, but tail pipes are still sooty. Does the MSD connect directly into the Stock EFI setup or do you have to wire in line somehow?

You can get the plugs that will allow you to just disconnect your stock Merc ignition and add the MSD set-up. No wire cutting is involved. This is a win, win situation, if the MSD craps out on you, all you have to do is disconnect it and plug in your stock system again. It is real easy to do. Just call MSD to get the right part #'s for the plugs before ordering.

Thanks, I will try that this winter for next years season