Hard idle until engine warms

[helixmhs]

I have a 2005 1900SR3 engine runs very ruff and stalls at idle when cold. I must force the engine to run at 2000 rmp for about 5 min until engine warms up, then I can idle. If I let the rpm drop below 2k the engine runs very ruff and can stall out. If I try to get going before engine warms up I can give it gas and the engine hesitates for 3-5 sec and has a hard time revving up (when cold). When warm boat runs well, rpm is in the 4500 range at wot and idle is around 600-700. Water sep is less then 1 year old, wires look in great shape. Any ideas?

[pascavone]

you have exhaust manifolds leaking raw sea water into the cylinders, when the boat is turned off for the night.

the sea water is getting the plugs wet, and this is causing the ruff idle until the engine heats up and drys out all the cylinders.

pull your spark plugs out the next time before starting the engine to check for water droplets on the plugs.

also, check for milky color oil, this is sea water running down the cylinder walls to the oil pan.

you would find milky oil under the oil filler cap.

[ss3964spd]

Um, water leaking into the cylinders is a bit extreme I think.

What engine is in the boat? If it isn't fuel injected then it sounds like nothing more than that the choke isn't operating properly.

Dan

[biggerseagar]

Whatever the engine what maintenance have you done? Water seperator should be new for this year. Carbs or fuel injecters? Last time you did a tune up?

Does the boat away for the season?

Roger

[helixmhs]

Thanks for everyones input. I have the v8 5 liter carb motor, owned the boat one season. I just change the oil, and no milky or abnormal oil issues (it looked good) Old filter and water separator were replaced Oct 2011 and again a few days ago. I went out tonight and pulled a plug (see attached photo) typical NGK plug # bpr6efs It looks in good shape and color (no water droplets) I found the spark plug wires are original mercury 6/14/2004 but "look" to be in excellent condition... I think it may be an issue with choke. I could not start it up at 9pm at night but I did look at the carb and noticed significant "junk" build up around choke. I assume the choke is electronically controlled, is it set on a timer? what should I expect to see when starting cold? I assume a full choke when starting and then it should slowly open? Any input? (looks like I cant get photos uploaded sorry)

[pascavone]

need to pull a plug on each side to be sure, could be only one manifold leaking.

[ss3964spd]

While not electronically operated, the choke is electrically operated. It is a simple affair; a flat, coiled spring inside the choke housing which connects to the choke plate via mechanical linkage. When the spring is cold it winds up a bit and, through the linkage, pulls the choke plate on the top front of the carb closed (or nearly so). When the engine starts 12V is applied to the choke coil spring which heats it up and causes it to un-wind a bit - thus gradually opening the choke over the course of, say, 5 or so minutes.

It is a rather simple check though. With the engine stone cold remove the flame arrestor on top of the carb. The choke plate should be closed. If it is not, operate the throttle briefly and see if it happens to close. If it does not close you've found your cold start problem.

Dan

[A Little Nauti]

Had the same problem. Replaced the choke and everything runs fine now, less than $30.00 fix. Checking your plugs for cylinder leaks is always good practice and if you do have a leak quite often you will have some back firing. Same as your water seperator. It will back fire big time if you don't replace it and you have water. Possibility of blowing out the valve seals when this happens. Simple fix is change your water seperator at the beginning of every season. Hope it works out well for you.