Not reaching max RPM on one engine.

[Dagenham Dave]

I just bought a 2019 SX210 and the engines should max out at 7800 rpm. I have read previous threads on this issue, but still have the problem. At max throttles, the port engine goes to 7800 rpm, but the starboard engine only goes to 7400, and boat speed is 39 mph.

1. The display panel records the boat's highest ever speed at over 46 mph.
2. Don't see any impeller problems with the naked eye from under and back of the boat.
3. Adjusted both throttle cables so the transducers go all the way to the wide open stops.
4. Replaced the spark plugs.
5. The color of the old plugs on both engines was light brown indicating good fuel mixture, with the middle cylinders on both engines maybe looking a little leaner.
6. I am running the boat on a river at sea level.

Any other ideas would be much appreciated.

 

[FSH 210 Sport]

The rpm difference between the engines is normal, with the port always revving higher than starboard, this has to do with the fact both engines turn the same direction and the way the pumps are loaded underway. The boats used to come with impellers that were pitched to the port and starboard side, but now they come with identical impellers. 7800 is pretty close to the rated rpm of 8000 but can easily be affected by temperature and altitude, since you are at sea level it would just be temperature. What was the temp when you experienced these rpms?

What is the oil level? I’m not exactly sure what engines that boat has but I’m going to guess the TR-1’s. It is important that you screw the dipstick in all the way when you are checking the oil level otherwise you will have an excessively high oil level and that can impact how high the revs go. Some have reported 500 rpm loss with too high of an oil level, and most run their oil level between half and full on the dipstick. If you needed to make a correction in oil level, then go out and test it….

Then

The other thing that can happen with too high of an oil level is the air filters can get fouled with oil. So before you go out next time, make sure the air boxes are clean, super clean, and when you get out on the water make two speed runs on the same stretch, up and back, then remove the air filter elements and make the same two runs again. Make these runs one after the other so you keep the same environmental conditions. If you pick up a couple hundred rpm by removing the air filter elements then replace them with a couple of RIVA gauze type air filters, this gave me 200 rpm at my altitude of 5000’.

Did you gap the plugs before you installed them? If the engines are indeed TR-1’s the gap should be set at .028”.

If there was a problem with your impellers your engines would rev high and cavitate, but it is good that you checked them.

What was the fuel load when you made this run? How many people and gear, E.G. weight was on board? Where were the people sitting ? These things can have a significant affect on speed, but the rpms will be the same.

What was the wind, temp and current? Were you looking at gps speed or water speed?

 

[Dagenham Dave]

Many thanks for all that info.
I have done several runs, all at about 80 degrees F with a fullish tank and just me onboard. They were on a river with extremely low flow and low wind. Checked in both directions and got the same rpms and water speeds.
I did gap the plugs before installation and the air filters looked pretty clean. However, I did a proper oil level check this morning and both engines were over filled, so I am about to go and remove the excess oil. I will then go check again, including removing the air filters and let you know results.
Thanks again.

 

[FSH 210 Sport]

Many thanks for all that info.
I have done several runs, all at about 80 degrees F with a fullish tank and just me onboard. They were on a river with extremely low flow and low wind. Checked in both directions and got the same rpms and water speeds.
I did gap the plugs before installation and the air filters looked pretty clean. However, I did a proper oil level check this morning and both engines were over filled, so I am about to go and remove the excess oil. I will then go check again, including removing the air filters and let you know results.
Thanks again.

Awesome! Hope you get some improvement! You’re very close to optimum.

Go to the NWS website and get me the altimeter reading, temp and dew point where you’re at and I’ll give density altitude.