Fling jet boat losing RPM's

[j_m_henderson]

I have a 94' Four Winns Fling Jet boat. 115hp V4 OMC-Turbo Jet. The prob. is that it will not run at full rpms. It started after a couple of trips around the lake@full speed. I idled a few minutes and then she would not come up to full power. I checked the obvious to me--IE Debris in the jet, and changed the fuel filter. The carbs have been recenty rebuilt by a shop,and the plugs changed.<br />Any Info would be nice. I am new to owning a boat, but not turning a wrench!<br />ThanksAny Info That Might Help johnh69@oldwiz.net

 

[Zebramidge]

Re: Fling jet boat losing RPM's

i have the same motor on a boston whaler jet boat recently purchased. have done similar maintenance but have yet to exceed 4750 rpm at wot even though i believe the boat should give more. cleaning up some small fuel leaks, replacing leaky vro pump and decarbonizing carbs added about 250 rpm. did compression test and got 140/135 starboard and 125/125 on port pistons. this 2 stroke is very smokey at startup. considering trying sythetic oil. what was your initial experience on rpm output? have you done comp test? have you experimented with different octane fuels?

 

[j_m_henderson]

Re: Fling jet boat losing RPM's

I have yet to do a compression check(planning on it) but I don't have a tach so I would have to guess that the rpms are around 45oo. The motor deffinately seems to need more power. I was going to fill with premium and a octane booster and hope I got some bad gas. But I also suspect the VRO pump, I'm afraid to know how much the pump is.<br /><br /> I have a friend who has a SeaDoo with 75hp and his boat is Fast! I have had trouble finding someone knowledgable of these motors. I can't even find someone to work on it here!<br /> IS there a place that you know of that has performance parts for these jets?(impeller,etc)

 

[Zebramidge]

Re: Fling jet boat losing RPM's

any omc dealer should be able to work on motor. some will have experience with jets and possibly a tank for testing. most won't. vro pump is much maligned but do a visual inspection first. is it leaking? i like j.b. cromwell's advice for first tests: compression and ignition: test each cylinder for 15lb variance at max, with motor running disconnect each plug wire and listen for drop in rpms. also visually test plug spark jump. simple test that tell alot. i'm no mech expert, but these simple test make sense to troubleshoot the obvious.

 

[j_m_henderson]

Re: Fling jet boat losing RPM's

I will try that. When I have called the boat shops around here and told them it was a jet boat, which is my mistake I guess. Next time I call I will just say that it is a omc and leave it at that. I'm not sure where and what the vro pump is? and what to look for to see if it needs maint.<br />waiting on a manual to arrive...<br />any thoughts?

 

[Zebramidge]

Re: Fling jet boat losing RPM's

everything i've seen on this board suggests jet foot is half as efficient as a prop. value to me is in skinny river water where prop guys are crapping their pants worrying about submerged day wreckers. omc motor manual is very detailed. i would wait til it bogs down and do aforementioned tests right on the water. do you see lots of smoke at startup and when it slows down?

 

[j_m_henderson]

Re: Fling jet boat losing RPM's

@start up first thing in the morning it has been sluggish on starting and requiring several cranks w/full choke. Then when it does fire, it will smoke initially and then quickly go away.