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1999 250 hp Won't idle, runs rich, fine @ WOT

mike77cj

Regular Contributor
I'm an I/O and carb outboard guy trying to help a buddy with his 1999 250 hp Saltwater Series II engine. Here's the deal:

* Boat was winterized and then sat for two years
* Uncovered last week, engine fired off fine, idles on muffs but does not idle in the water
* If you start it and rev it up, then quickly throw in gear it will run fine, 1400 rpm and up
* Engine runs flawless from 2500 all the way to WOT

I replaced the fuel filter and bypassed the boat's tank with two small 6 gallon tanks to rule out tank issues. We ran two cans of SeaFoam through the engine at 2 oz / gal. Checked spark on all six and it looks good. New plugs, gapped correctly.

There is a LOT of fuel blowing out of the exhaust at idle.

Again, I am not familiar with these outboards.... How does the ECM regulate fuel control at idle? When the engine is cold does it run in an open loop, then switch to closed once warm? Is there an O2 that could be affecting the mixture?

We also check the high pressure pump to ensure the float, needle and seat weren't clogged.

Any and all ideas here would be greatly appreciated.

Thanks!
 
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