Both Engines Limited to 9,000 RPM, WHY?

[swatski]

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.

An impeller's pitch, particularly the trailing edge angle, will determine the max RPM (for any given engine/pump).
If those impellers are different make/model and /or pitch than OEM, all bets are off.
Same as regular props, really, except an impeller will have a set blade diameter, but the pitch will determine RPM.

 

[0627Devildog]

Could altitude be a factor here?

 

[Bruce]

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.

An over pitched impeller will provide greater acceleration at the low end but will consume all the available torque before the engine reaches max RPM.

An under pitched or damaged impeller will move less water per RPM allowing the engine to reach max RPM earlier than expected while producing a lower top speed.

Changing the pitch of the impeller can increase top of bottom end. Changing the design of the impeller can increase of decrease both.

It is likely that he has impellers that need to be depitched to bring RPM and top speed closer to expected. This often happens when owners switch to aftermarket impellers.

 

[Bruce]

Could altitude be a factor here?

Good point, what altitude are you boating at?

 

[AZ Native]

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.

There are no markings on the engine or side of the boat that indicate HO. But, the recent Yamaha tech (works on jet skis not the boats) swore that it's an HO because the intakes have horn like adapters with the screens on top of them. I really don't know what I have. I don't know Yamaha's markings in 2005. I can take some pictures of the engines to post.

The Arizona Desert lakes are at maybe 1,300 to 1,400 feet. Altitude is definitely not the issue.

 

[Bruce]

There should be a data plate low on the front of the engine compartment lid. Each engine should have a plate underneath near the starter.

 

[swatski]

Could altitude be a factor here?

That, and also humidity.

 

[AZ Native]

That, and also humidity.

That's almost funny. I'm in the AZ desert at 1,200 feet, we don't know what humidity is. It's a dry heat.

 

[scokill]

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

Are we still talking about boats??

 

[Bruce]

Pulling the pumps should be easy. The first time I pulled mine I had to gently use the pry points that are built into the pump housings. It has come off easily ever since. Make sure to apply moly grease to the spline before reassembly and use thread sealant on the bolts. Adding a little RTV between the pump sections is a nice touch. I also grease all of the steering and reverse parts when reassembling.

Once you have them apart post pictures of the impellers and the part numbers found on them.

This video documents the pump removal well.

 

[Dieselpwr]

High Output boats say High Output on each tachometer.

 

[Julian]

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

We pride ourselves in the speed we dive in on issues like this! If you are on the water and need help, start a new thread and put the @ symbol and the word "help" in the body of the post and it notifies those via their preferred alert mechanism and we have an average 4 minute reply time! Now that is AWESOME!

Post up some pick of the impellers once you have them out...but after market impellers is a likely culprit. If they overfilled the oil and you've not removed it down to the right level it is possible your plugs are fouled again. These engines are VERY sensitive to fouled plugs....

 

[AZ Native]

I went to the storage lot and shot a few pics. The tach's don't say HO. Note the year of manufacturer and the gate positions at WOT. These engines only have about 115 hours on them. It will be a few days, maybe a week, before I can pull the impeller apart. I'll send more pics. I have some mechanical skills and hate spending big bucks with a dealer giving me the run around. And, yes that's a custom aluminum trailer I had built for it.

 

[Bruce]

SRT1000BD is a normal MR-1 boat, not a High Output. The high output versions start with SRT1100.

 

[Bruce]

This review documented 48.1 MPH @ 10,000 RPM for your model in new condition http://www.boattest.com/oem/403/boats/663/0/on/640x360

I am sticking with the theory that you have over pitched impellers.

Your impellers should be

Impeller STBD 16.3 DEGREES 68N-R1321-10-00
Impeller PORT 17.3 DEGREES 6B5-R1321-00-00

I would not be surprised if someone installed HO impellers that are more aggressively pitched.

 

[Dieselpwr]

Those are the non high output 140hp motors.

 

[scokill]

This review documented 48.1 MPH @ 10,000 RPM for your model in new condition http://www.boattest.com/oem/403/boats/663/0/on/640x360

I am sticking with the theory that you have over pitched impellers.

Your impellers should be

Impeller STBD 16.3 DEGREES 68N-R1321-10-00
Impeller PORT 17.3 DEGREES 6B5-R1321-00-00

I would not be surprised if someone installed HO impellers that are more aggressively pitched.

Interesting that the non HO is reviewed at 48.1 mph. My newer HO might get that on a good day. I think I've sniffed 49 before, but I'm a little surprised at that speed.

 

[AZ Native]

Tearing down the pumps and inspecting the impellers will be the next project. Bruce, you've given me a lot of great information to work from. I should probably repack or replace bearings as long as I'm taking the pumps apart. Any good threads for that process would helpful. As soon as I have more pump info I will be back to this thread.

 

[Bruce]

I am not suggesting going this far but there is lots of bearing info in this thread https://jetboaters.net/threads/changing-yamaha-jet-boat-pump-duct-housing-bearings-and-switching-to-oil-bath-lubrication.10155/

 

[swatski]

Tearing down the pumps and inspecting the impellers will be the next project. Bruce, you've given me a lot of great information to work from. I should probably repack or replace bearings as long as I'm taking the pumps apart. Any good threads for that process would helpful. As soon as I have more pump info I will be back to this thread.

@Bruce great info!

However, the engine sticker says 95.6kW which is roughly an equivalent of 128 ponies. And the engine was built is 04, may be not the exact model tested by boattest?
Possibly this is yet another version of the MR-1 ? Just a bit shy of 140 (which would correspond to 104kW) -- and that might explain the RPM right there.

I bet you the impellers are stock.

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