Help! Boat will not start in water, but will start on trailer with flusher attached

[macattak17]

I have a merc sport jet 240 in my 2000 seadoo speedster, the boat is new to me so i am not sure what to do, it starts fine out of water but not in water. i noticed that both exhaust ports are fully submerged, i don't know if that is normal for this boat. Yesterday i pulled all the plugs out and water drained out the bottom left cylinder, i read that if you have to much pressure when you attach the flusher it can back feed into the engine, so i have dried all the plugs and turned over the engine, and it starts every time with less water pressure....when in my driveway..., after i started it in my drive way it was not 15 min later i put it in the water any nothing it was turning and turning but no ignition .. im just wondering if any knows whats the problem or what to do.

 

[Dr Honda]

Yes... it's normal for the exhaust outlet to be under the water. It helps keep it quiet.

You shouldn't get any water into the engine, if on the hose. It should just drain. SO... something in the cooling system is clogged... or you have a bad head gasket.

Since the boat is new to you... have you checked the compression?

 

[macattak17]

to be honest i bought the boat as a project boat, and put a fully rebuilt engine in it, it cost be alot more than i thought it was going to be but the boat is now a labor of love lol... so i would assume that the head gasket it okay because its all new. however i know that it could be a possibility, it has not had any water in the cylinder since i have lowered the water pressure coming from my house. it starts every time with out hesitation in my driveway, but will only turn over and over and over when in water. correct me if i am wrong, but i have been researching quite a bit on why this would be happening and one of the reasons i found was that my idle is to low. when its at idle in my driveway its idling at about 900-1000 rpm, i read that it should be double the rpm when out of water because there is not a full load on the engine, the manual says it should be about 1000-1100 rpm at idle on water, so it should be around 2000 rpm when out of water, could that be the reason why it wont start in the water? because im only getting like 450rpm when under full load?(half of what it is when out of water)

 

[Dr Honda]

Yes... absolutely. If you are idling that low... it may never start.


I'm not sure if I would bring it up to 2000 out of the water.... but I would bring it up to 1200~1500, and try again.


But I would still check over the cooling hoses. It's very hard to get enough pressure to get water into the engine on a Merc. Officially... you don't have to run the engine to flush it. SO... water shouldn't be getting into cyl's.

 

[El Toro 33809]

Is the steering assist hooked up to your boat? If so, turn the wheel all the way to one side or the other when you try cranking it under load. But do what Dr. Honda says, check the hoses and up the idle speed.