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Quote:

Originally Posted by rexcramer1 (Post 3349344)

Since you changed the battery it may have run extra rich for a short period of time until the computer "relearned" the parameters for your engine and elevation as well

There is nothing to relearn. These engines do not have O2 sensors for feedback.

Is it worth having them re-programed to get burn less fuel and have less soot on the boat? With gas prices getting higher and higher all the time, I would not mind saving a little gas. Could that help performance?

I think that leaning them out at idle would be a good idea. Not only does it save on cleaning the transom, those guys with alot of idling will be happy to not load plugs up all the time as well. 13:1 would be a nice consevative start.

That is where I set up my carb. 500. never had an issue in 150 hours.

Quote:

Originally Posted by billeickmann (Post 3352469)

I have not yet seen what the stock air/fuel curve looks like on the 500EFI's, but the 500HP before it was 11.6:1 A/F at idle and never crested 12.0 until after 3000rpm.

What you really need is a wideband O2 monitor to see where your engine is at now. Once you know how lean or rich it is, then you'll know what you have to modify and gain.

Quote:

Originally Posted by aaronniquette (Post 3344642)

i have 500 efi and have ran the boat at lake tahoe all of its life 6800 foot elevatiin. I brought the boat down to lake mead at 1100 foot elevation and put new battries in it. I went out and ran it. The boat ran perfect 5100 spinning 30 pitch props. When I pulled the boat out on the trailer I noticed a very black transom. The fuel in the boat was 4 months old. I added 15 gallons fresh 91 fuel to the boat. could the black on the back be from marginal fuel? Or the elevation change? the boat did not run as if it had any issues.

I have a pair of '05 525 EFI's in my boat and I also called Mercury Racing. They told me to have the ECM's removed by a certified Mercruiser dealer and send them back to Mercury and they would reprogram them, (under warranty), to make the engine run leaner at idle speeds. They told me their original set up was a little too rich at idle RPM's causing sooting on the transom. They are currently on their way to Wisconsin as I type this message.