Help Worst Day of My Boating Life

I've had my boat for almost a year now. Its a 1995
Moomba Boomerang Direct Drive 351 PCM engine. When we got it, it was always hard to start, you would have to pump the throttle while you turned the key and it would always have a problem idling. It would idle rough mostly when you first start it and would continue through out the day.

Middle of last year we:
We got the carburetor rebuilt, cleaned the fuel tank, the fuel lines, added a fuel water separator, replaced the coil, spark plugs, distributor cap, and fuel lines.

After all of that it worked fine, it would start up every time you turned the key and would run great through out the day. lately it would occasionally run rough during idle/neutral and when I first put the boat in, but after I gave it some gas in neutral and ran it around a little, it would run fine.

Well today we get the boat out and it starts up no problem, but is idling very rough and then just quit. I got it started again and reved the engine in neutral to get it to warmed up. We rode around a little and then stopped to see how it was doing. As soon as it went back into idle/neutral it started rough again. It would get worse and worse until it just shut off. I finally got it started back again and drove back to the dock no problem I even circled around near the dock at a little over idle, but as soon as i dropped to idle/neutral. The problem started back and soon shut off. This time I couldn't get it to start back.

Luckly we were close to the dock, but were just far enough to need a tow. Someone towed us back and I ended up putting the boat up.

Anyone have any idea where to start with this? I've had people tell me to check the choke, idle control screws, dirty spark resignator, etc. Could it not be getting enough air in the engine compartment, to much dirty air? I'm stuck and I haven't been out on the lake for the past 3 weekends and its killing me.

It could be about a dozen different things, but if it were me I would start with the most likely first.

Check the fuel filter, both the canister type inline and also the small screen type on the carb inlet.

Sounds to me like a fuel issue, either fuel flow or pressure. Check the fuel pump for proper flow. Sometimes it is easier to replace minor "wear-out" type parts and diagnose that way.

Good Luck. Sean

it runs good ok off of idle so its not going to be a fuel psi issue. Your carb is going to be the issue, or you have a intake leak.

Where would I look for an intake leak?

start the eng & hold your hand above the carb. if the idle smothens out you are running too lean. Check for leaks with a can of brake clean. when you find the air leak the rpm`s will raise up when sprayed on the spot.

If it ran fine when you put it up last yr, it probably just has some crap in the idle circuit. Does it run OK at 3k rpm?

You can try this, get it idleing at the dock with the air cleaner off. While revving the engine a bit in NEUTRAL, plop a big rag over the carb and blip the throttle hard. It sucks air hard through the little idle passages that get clogged up when the boat sits. It may clean out the idle circuits, try it a couple of times. If not, take it to a shop and have them clean out and tune the carb.

You can get a vacuum gauge really cheap at an auto supply store. That will help you.
Instructions are usually packed with it.

Sounds like a vacuum leak or carb issue to me.

Tighten all the fasteners on the carb (this may involve removing the carb to check underneath) and the carb to intake nuts. You can find a leak (if the engine rund long enough) by carefully spraying Brake Clean on the intake/carb area and if the RPMS increase you've found the leak.

There also may be debris stuck in the idle circuit. To solve that, remove the idle mixture screws (counting how many turns they are from bottoming out first). Then clean the cone shaped mixture screw and blow compressed air into the hole to clear the circuit. Reassemble.

if this is your worst day ever, you have either done very very little boating or been very very lucky

Thanks alot guys for the help,

I hate Winter:
I tightened the bolts on the front and rear bowls, they all turned at least 1-1 1/2 turns each. Also took out the Idle mixture screws and (they looked fine BTW) and blew air into the holes.

Psyclone:
Thanks for the suggestion, I will try that possibly later today or tomorrow once I am able to get back on the water.

Also what do I do if I find a leak with the brake cleaner method?
Also at this point my boat wont even start. I figured yesterday that it was just flooded, but it should be fine by now right? Normally I just turn the key and it starts right up, if not pump it some gas until it turns over, but thats what got me flooded the other day. Any suggestions on that?

Supra for Me: I didn't quite tell all the events of my whole day, There were a couple of trips back and forth to the house to pick up keys/drain plug for my girlfriends boat(that hasn't been out in over a year). Also we had several problems getting her boat to start, battery and electrical problems. Needless to say we weren't able to get out on either boat and tensions were high.

I had a similiar problem not exacatly the same but it was hard starting then hard idling until it warmed up then it would be fine....I thought carb issue or fuel issue. But after I tried a ton of things I took it to the shop to be fixed and turns out all it was was spark plugs. I know you said you changed yours last year but I did to. Its something simple and inexpensive to check before you go tearing up your carb...Good Luck!

I think supra ment as long as no one was hurt no insurance clamis were filed, it could have been worse. Good luck.

let me make your worst day seem trivial:
my worst day we hit an island and totally smashed the boat, ejecting people, nobody got seriously hurt, another worst day we had the shaft snap and lost the prop and luckily got towed by the sherrif 10 miles back to the marina
happy boating
i am goin out footin today

You said you had changed the distributor cap. Did you also change the rotor? I don't think it's ignition because that would usually show up worse on full throttle but you never know.

Another thing you can do is remove some of the spark plugs and see what color range you have. Black sooty plugs are a sign of rich burn which could be caused by several things including a vacuum leak, late timing, or a defect in the carb itself.
Normal color should be tannish.