Mercruiser 5.0 Stalling when reducing RPM's

[mccutchen]

Hi all. I have a 2005 5.0L Mercruiser engine with a carb. and an Alpha 1 drive. I had the boat in storage in Florida (so warm weather) for a little over a year without any running. When I took it out the first time after this storage period, I was having problems with it stalling at Idle. The choke is working as the RPM's go up to about 1500 when it's cold and then work their way down to about 800 RPM. The problem is, in drive or neutral, when I'm at higher RPM's (above about 1800 or 2000) it runs fine and then as I come back down closer to idle or less than that, it drops right off and stalls. Once it's warmed up, it will start right up and idle forever, however even once warm, when I increase the RPM's and come back down, it stalls every time, whether I do it fast or slow. I had to leave on business for that year on short notice and didn't get out to "winterize" the boat before storing it.

Are there things that can happen after a year long storage that could cause this? So far I have changed the fuel filter, added stabilizer and the Star Tron Enzyme Fuel Treatment to the fuel, changed the oil, cleaned the flame arrestor, and cleaned the carb inside and out with carb cleaner (not disassembled). Keep in mind it only sat for a year, in Florida, and it's a 2005 so not that old. It ran great and didn't show any signs of this prior to storage.

My guesses are:
1. Bad fuel (how can I test this and why wouldn't the treatments help)
2. Plugs maybe got corroded since I didn't fog the cylinders
3. Something going on with the carb though I wouldn't think sitting for a year would cause this.

Any input on what's common or what to look for would be a huge help. Thanks!

 

[Don S]

Re: Mercruiser 5.0 Stalling when reducing RPM's

Possibly fuel problems. Did you check the filter contents for water? May be a slightly plugged up idle circuit in the carb.


If it's just a little dirt in the carb, here's a trick that MIGHT work. Engine warmed up and running on muffs or in the water (drive down) remove the flame arrestor and disconnect the throttle cable.
Here is what you do. Rev the engine up to 3-4K rpm and close the choke. But not so much that the engine dies, open it back up and get it revved up again and repeat. This may just clean that little bit of dirt out of the idle circuit.

If you do let the engine stall, It will be flooded. Hold the throttle to wide open, choke open and start the engine.

Good luck.