Both Engines Limited to 9,000 RPM, WHY?

[AZ Native]

Bought a 2005 AR230 this summer. So far I have yet to see more than 9,000 RMP out of either engine. Just had the oil changed, lots of oil in both intake boxes. New air filters. They run 10,500 RPM on a hose, but only 9,000 RPM in the water. I'd like to trouble shoot myself, but don't know where to start. Searches always lead to ECU, injector and coil issues, but both engines are running identically. I know these engines should put out in excess of 10,000 RPM.

Any questions, input and advice would be very welcome. The other forum has been no help at all.

 

[scokill]

You shouldn't run 10,000 rpms on hose....there is no load on the pumps. You could damage the engine. If you you oil in air box your engines are overfilled with oil. You need to suck out oil until it barely reaches the dipstick on the trailer. Pull your air filters, clean up air box, don't put them back in. Change your sparkplugs and go back on the lake. Warm up and check oil. It should be between L and H mark. Adjust if needed.

 

[AZ Native]

You shouldn't run 10,000 rpms on hose....there is no load on the pumps. You could damage the engine. If you you oil in air box your engines are overfilled with oil. You need to suck out oil until it barely reaches the dipstick on the trailer. Pull your air filters, clean up air box, don't put them back in. Change your sparkplugs and go back on the lake. Warm up and check oil. It should be between L and H mark. Adjust if needed.

When I had the oil changed last week I gave specific instructions like your recommendations. They also installed new plugs. Still the both engines only top out at 9,000. Does a little oil make that big a difference in performance?

BWT the engines only have about 115 hours on them, it's always been a fresh water Arizona boat. I was told by the tech that the impellers and nozzles are in fine shape. Also, the Starboard engine runs a little rougher at idle and startup and slightly slower at top speed than the Port engine.

 

[Murf'n'surf]

Could be pump related. Make sure your impellers are installed on the correct side. They are pitched differently between port and starboard. I believe the port should have ribs in the metal collar. In addition to the correct positioning of impellers, check the clearances between impeller blades and housing. There should be a close gap like 2 business cards thick. Large missing chunks and gouges can lead to performance loss and cavitation. Check the impeller blades for dings and bends-- those can cause performance loss as well. Please feel free to post pics for us to diagnose.

Fuel -- is it old? New?

Got any fuel smell in the exhaust while running?

Many possibilities but we shall find your problem!

 

[AZ Native]

I appreciate the quick and enthusiastic positive responses.
The fuel is new.
Compression in all cylinders in upper 170's.
No fuel smell while running.
The only obvious issue was the oil in the intake boxes and soaked filters. That's why I had the oil and plugs changed.

I guess the next step is to drop the pumps and take a closer look. I've considered bearings, impellers. Got to find a cool place to work on it. 110 degree weather on the pavement isn't fun for service work.
This is my first jet boat and twin engines both acting up with the same slow performance strikes me as odd. You would think trouble or issues would occur on one side or the other, but not both.

 

[scokill]

When I had the oil changed last week I gave specific instructions like your recommendations. They also installed new plugs. Still the both engines only top out at 9,000. Does a little oil make that big a difference in performance?

BWT the engines only have about 115 hours on them, it's always been a fresh water Arizona boat. I was told by the tech that the impellers and nozzles are in fine shape. Also, the Starboard engine runs a little rougher at idle and startup and slightly slower at top speed than the Port engine.

If oil soaks air filters, yes. Just trying to eliminate possibility. Murf could be on the right track though....impellers could have been repitched. What is your top speed?

 

[AZ Native]

I'm getting maybe 37 to 38 MPH top speed. Verified with a GPS. The speedo climbs to 45 during a slow left turn, but I chalk that up to the way the impeller is in the slip stream. I figure I should be getting 10,200 RPM and 45 to 47 MPH. I did install Thrust Vectors before my first outing but can't imagine they impact performance.

 

[Murf'n'surf]

While on the trailer, check the reverse gate clearance in full forward. It's a long shot but make sure they are getting up and out of the way. A low gate usually causes vibration in your throttles.

 

[Bruce]

I would guess that your impellers are non stock and not the correct pitch or the air filters are oil soaked. First I would remove the air filters and verify the oil level and see what she does. After that I suggest pulling the pumps and checking the part numbers on the impellers.

 

[swatski]

Adjust throttle cables?
Unlikely they both have same slack, but who knows.

 

[swatski]

First I would remove the air filters and verify the oil level and see what she does.

Removing the filters and running without (to test the effect on RPM)?

 

[Bruce]

Removing the filters and running without (to test the effect on RPM)?

If a MR1 is overfilled with oil it spits it out into the air filter. From that point on it is sucking oil in which reduces power. If he pulls the air filters to test he takes them out of the equation. The filters are expensive so MR1 owners tend to be careful about not overfilling.

I think it is more likely that the impellers are too aggressive. But it is worth verifying that oil is not the issue.

 

[Murf'n'surf]

10 mph loss is big..... Gotta be in the pumps. Impellers, housing or bearings.
Oil soaked filters would cause bigger issues....I think.

 

[Bruce]

10 mph loss is big..... Gotta be in the pumps. Impellers, housing or bearings.
Oil soaked filters would cause bigger issues....I think.

I also think the impellers are the most likely culprit.

 

[Scottintexas]

since both engines can achieve 10k rpm out of the water we know the linkage is ok and the engines can do it,
since both engines only go 9k rpm in the water I don't think it's a pump/cavitation/plug issue that would usually only affect one side

since this is an '05 and new to you boat I would also suspect aftermarket impeller pitch and not damage to the impeller,

it's easy to pull them yourself, check out our FAQ section for a walk through, it's about a 30 minute job,

maybe they will have some markings to help you identify them, if the stock impellers were repitched you may not see anything obvious,

 

[bronze_10]

Could it be a carb boat???

 

[AZ Native]

When I first realized the air filters were soaked with oil, I did remove them on the lake and experienced a 150 RPM increase in each engine (also significantly increased noise at full power). So there is my contribution to the FAQ. But 9,150 RPM isn't 10,200. So yes I can attest that soaked filters impact performance, but doesn't explain this 1,000 RPM loss in both engines. Frankly after market or reversed impellers are sounding like the next investigation. I hope they're as easy to pull as you indicate. I've read horror stories on other forums about pulling the shaft once the housing is off.

BTW: the response and advice on this forum is light years better than the other one. I'm feeling the love.

 

[Marvin willis]

I would think if the impellers were a diff pitch it would still hit the rpms just not the speed. It is a ho correct? Didn't I read that it will hit 9000rpms on three cylinders. Even though I find it hard to believe that both motors are running on 3.

 

[Marvin willis]

The shaft just slips out easily. Mine came out easily after 11 years

 

[swatski]

The shaft just slips out easily. Mine came out easily after 11 years

The bigger issue maybe pulling the impellers of the shafts, if that ends up being necessary.