Choppy idle and sporadic top-end

[twinpartners]

Hopefully an easy one

3 Cylinder Rotax in a 2004 Seadoo 4-TEC Sportster. I'm in Florida...salt water. Took the boat out after it sat for about 2 months and here is what I got:

The idle is rough...I like to call "choppy"
When I pull the spark plug wire (while running) nearest the back of the boat...no difference...still choppy
When I pull the middle spark plug wire (while running)...still choppy and no difference...
When I put them both back and pull the rear spark plug wire (other two are connected to the spark plugs)..the engine stops.
No cranking problems...starts right up every time. Its just rough at idle and there is no top end...like I am only running on one or two cylinders.

When I am in the water...I can get to 30'ish MPH at full throttle and you can tell that the engine is choppy.
While I am gliding on the water...every once in a while the whole engine "kicks in" and is smooth
It revs high as if all cylinders have kicked in for about a second...but immediately goes back to being choppy.

I have a feeling like I have a spark issue, but can't be 100% sure. I just rebuilt the lower end and there is no cavitation issues. Its definitely coming from the engine (chop/chop).
Not sure if its spark or fuel (clogging). I put a can of SeaFoam in the tank at the last fill up hoping it would resolve any fuel related issues.
Gas is also new....so its not old gas.

Thoughts???

Any ideas? BTW...compression is great on all 3 cylinders.

 

[pwgsx]

Check the ICV and TPS. Might need to replace both.

 

[purple_people_eater]

are the spark plugs new? start there. especially if its an sc'ed boat. i've had a brand new set of plugs only last an hour.

 

[Sportster-2001-951C-Stock]

I'd remove the injector rail and give it a crank while watching for spray into a rag to catch the fuel, and while out I'd look for injector dripping. The other fuel system check would be to verify pressure.

There was a thread on here somewhere the owner had trouble with injector firing and the problem was finally traced to a fuse box.

The other side to check carefully is the ignition system, of course. An old indian trick that sometimes helps to locate a fouled spark plug is if holding the plug cap about 3/4 inch off the plug and letting the spark jump to the plug causes that plug to begin firing, the plug is fouled. The reason is, this allows the spark voltage to increase where otherwise a leaky plug would bleed the voltage off slowly and voltage might not rise high enough to jump the gap.

 

[twinpartners]

Check the ICV and TPS. Might need to replace both.

I think the ICV is just fine. Idle RPMs are okay...the engine is just not running "smooth".
Great idea on the TPS. I decided to order new ignition coils, TPS, and spark plugs.

Thx!

 

[Sportster-2001-951C-Stock]

Good idea on the TPS as well, those are known trouble makers.

 

[twinpartners]

Fixed

3 new coils and 3 NGK spark plugs is all it took. TPS has not arrived yet, but will keep it in my private inventory if I ever need it.
Only 1 of the 3 old coils was still good (the idling cylinder....go figure).

 

[donphantasmo]

I would invest in a CANDOO. That thing is awesome, and well worth every penny. It seems expensive, but if you take your boat to a dealership, they'll give you a 300-500 bill almost every time. With the candoo, you can trouble shoot your own. The thing I like about it, is that you can turn on and off each injector, and each spark plug.

You would have found out exactly what is wrong with your boat, the first day. Along with making extra keys, and even putting your personal information in the computer, so if your boat gets stolen, and it goes to a shop, they'll know who the owner is.

I don't work for Candoo, I'm just very happy with their product and their support.