New member here! Problem with acceleration

[Kjwall4]

I have a 1996 F16 Sea Raydor. Does anyone have problems with their jet boats running full throttle with a full tank of gas? I filled up the tank and couldn't get over 10 mph. I was having to jump in and clear out weeds from the grate cover. But when it was clear, it would go but not over 10 mph. Any thoughts? I put premium gas in as that is what it was run on from the previous owner. I can see through the impeller and do not see any obstruction. First time we had it out with friends and was bummed it wasn't working like it should. Thanks in advance.

 

[haknslash]

I don’t know anything about that boat or engine.

Is the engine running strong but just no thrust?

If it’s bogging:
Is it carburetor or fuel injected? Is it a new purchase or you’ve had it for years and all the sudden isn’t running well? If you just bought it or it’s new to you then I would go over the basics like fuel system (fuel filter, pump, injectors or carb jets), new spark plugs, air filter etc.

If no thrust:
Is there cavitation (feels like slipping clutch on a manual car or spinning tires in mud)? If there is cavitation how does the impeller look? Any burns, rough edges or pitting? What does the gap look like between the impeller and wear ring?

How did it run without friends in the boat?

I’m sure others will chime in, perhaps even those familiar with the boat. Just going off what is check first.

 

[Julian]

Agree with @haknslash my guess is one or all, or some of the following:

1. the tolerance in the pump is out of spec (gap is too big between edge of impeller and sleeve
2. The intake tunnel is missing sealant
3. The impellers themselves are damaged

 

[Kjwall4]

It ran great the last couple times out with wife and kid. Impeller looks good, no gap. Only thing different was I filled it with gas and we sucked up weeds. Do I need to flush it out? How would I do that?

 

[Julian]

It ran great the last couple times out with wife and kid. Impeller looks good, no gap. Only thing different was I filled it with gas and we sucked up weeds. Do I need to flush it out? How would I do that?

Is it possible you got bad gas?

 

[Kjwall4]

Maybe. Engine doesn't skip or sputter. Put in Premium gas with no ethanol from the pump at the station

 

[Julian]

Maybe. Engine doesn't skip or sputter. Put in Premium gas with no ethanol from the pump at the station

You mention weeds...are you sure you didn't still have weeds on the grate? Are you familiar with the reverse maneuver?

 

[Kjwall4]

Yes. I removed weeds several times. I am going to take it to a lake where I know there are very little weeds and see what happens. Thanks for the input everyone.

 

[biffdotorg]

The real question is: When you say it only went 10mph, was the engine at full RPM, or bogged down.

This determines if it is a fuel problem or cavitation problem. As you didn't really say above.

If the engine was bogged, or would not hit full RPM, then you can guess you have a fuel/engine issue. If it sits still and hits top RPM, then you have a cavitation issue and you have not cleared the pump from Grate to Nozzle. And yes, a full tank of fuel would add weight to the boat, but if there were no cavitation, the boat should be able to plane out with a proper load.

The times that weeds can cause issues other than cavitation is if you blocked a water intake and the engine is overheating. But that would not be common in this case. If I am putting around, and I don't see water coming out of the pissers, I know that she's gonna throw an overheat alarm, and I can expect my pump to be clogged with weeds.

I'm guessing this is a 180 or 210 Merc Sportjet?

 

[Kjwall4]

I get full rpm. I have a Merc 120xr engine

 

[biffdotorg]

I get full rpm. I have a Merc 120xr engine

Then this is hardly a fuel issue if the engine is running that well. The last Merc Sportjet I ran was twice that size, but so was the boat. You have little room for overload at 120hp. That pump is probably pretty tiny.

So the chances of cavitation with the slightest bit of weeds is very possible. I see what a small amount does with our bigger pumps. 90% chance you still have some crap in there. While on the trailer, shine a light in the grate and look into the outlet of the pump nozzle, and vice versa, you may be surprised what is still in there. Cavitation is pretty simple to find root cause for.

Good luck,