57L 4bbl rough idle

"I have a 5.7L mercruiser with

"I have a 5.7L mercruiser with weber 4bbl carb. During dewinterization, the engine was idling rough (hunting rpm, stall at low rpm). I fixed the timing which was way off, and replaced a corroded distributor cap and rotor. Still rough idle. I pulled the plugs (new end of last season) and checked compression on the cylinders. The plugs were black and wet with gas. The cylinders had anywhere from 140# to 168#. The manual references 150#, and the lowest compression cylinders had the least fouled plugs. The cylinder at 168# was the wettest of all.
I am lost here now. Should I clean up the plugs and give it another shot? Is 800rpm too high at idle? The manual references 650-750rpm in forward gear, can this be correlated to an idle rpm? Can bad gas cause all of the above (I used stabilizer all winter)? Is a carb rebuild the next step or is there other troubleshooting that I can do?
Thanks in advance for your time and support.
Matt"

"hmmm timing shouldn't jus

"hmmm timing shouldn't just go off....
was it advanced or retarded?
If Adv- Check the advance weights in the distributor for stuck corroded weights and springs.
If ret., check if timing chain has stretched.
Double check the firing order- plug wires."

"[b]"Is a carb rebuild the

""Is a carb rebuild the next step or is there other troubleshooting that I can do?"

Ayuh,...

Black,+ wet plugs says it's over fueling,...
Could be bad gas, but I doubt it...
Stuck float,.. Maybe,..??

You might want to recheck what you've done,..
I agree with HyStat,.. The timing usually doesn't just Change...."

"New Plugs. Then bypass the fu

"New Plugs. Then bypass the fuel tank, at the fuel pump, with fresh fuel. A hose stuck in a gas can will work."

"Thanks, guys. To clarify abo

"Thanks, guys. To clarify about the timing...I was wiping it down and checking connections before turning it over and noticed the distrib/cap was loose as could be! Don't know how long she ran like that before I winterized it, but I set it and tightened down. It was 40deg BTDC (vs 8deg BTDC)!
As far as bad gas goes, when I picked the boat up from the yard in the fall, they did give me bad gas. After replacing the gas tank and filling with 150 gallons of gas on a Wednesday, they pumped out 15 gallons of water out of the tank when picked it up the following Saturday. Needless to say, I will not be returning to that yard. I dumped in lots of Stabilizer, changed the fuel filters, and ran her until it seems to clear out. Then I changed the plugs with new and ran again for only ~5hrs before winterizing. She seemed to run well in the fall and I can't imagine how the plugs got so fouled so quick. I continued to add Stabilizer about every 2 months through the winter.
I think I'm going to see if I can clean the plugs up and try clean gas to the pump.
Anyone have any guidance on idle rpm on these engines? Where should I expect it to be at? Do I need to adjust my throttles cables if she stalls with the throttles all the way down (<750rpm)?

Thanks,
Matt"

"you have it right 650-750 in

"you have it right 650-750 in gear "in water", about 800 out, also if you have thunderbolt ignition(electronic) you'll need to either ground a wire or use a jumper wire to disable the initial advance and to put the ignition module into base mode to set the timing.

I like to then set idle with throttle cable disconnected, then adjust cable with a little pressure to hold the throttle to idle"

"Thanks everyone for your inpu

"Thanks everyone for your input. Is there anything I can do to treat the 150 gallons that I've got in there? Octane booster or Fuel Stabilizer? I hate to scrap all that fuel ($$$).
Also, is there an "idle" rpm that I should be shooting for, or is checking the rpm "in gear" the only way to do it. I am looking to understand what I should aim for before I leave the dock.

Thanks again,
Matt"

Brian said; "you have it r

Brian said; "you have it right 650-750 in gear "in water". Tie the boat securely to the dock.

Don't use octane boosters since they will foul your plugs. Startron makes a water dispersant for gasoline. Others are also available like Stabil.

"Pump the fuel in to your car

"Pump the fuel in to your car or truck. These are less fussy about what you feed em.
If plugs are fouled and you clean them, they will foul real soon because of the removal of the factory coating. New plugs will be the only way to eliminate that possibility."