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.

 

[Dagenham Dave]

I took 7 pints of oil out of the two engines in total! Now the port engine looks like 7900 rpm and the starboard 7600, but I am only getting 40 mph.

Elevation 16', temp 81 degF, dewpoint 70 degF.

 

[Dagenham Dave]

Removing the air filters had no noticeable impact.

 

[FSH 210 Sport]

Your density altitude was 1717’, I had to make a guess on the altimeter setting. So roughly a 5% horsepower loss, and could could easily account for the 100 rpm loss. Good news is you picked up a bit of rpms, and corrected excessively overfilled engines, roughly 50% per engine if I have that correct. You are there on the port engine, and the starboard is pretty close.



Good news on the air filters.

So, I should have told you to do this as well, but its not that important to finding rpm as it is to learning how accurate your tachometers are.

The next time you go out and are at WOT, start pulling the port throttle back until you hear the engines synch up, take note how many rpms the port engine is, and or how many rpm you had to decrease the port engine to synch with the starboard. I was told by one of the aftermarket companies that the tachs, especially the analog ones, are not that accurate / reliable. By doing the aforementioned test of synching the engines you will get an idea of how many rpm the engines are truly off by. For example, currently your tachs show the two engines are off by 300 rpm, but if you pull the port down by 200 rpm to 7700 and the engines are synched then the engines are only off approximately 200 rpm.

Make sense?

Once the weather cools off a bit your port engine will be maxed out and the starboard will come up as well. Its just the nature of the design that the rpm do not match. The only thing you can probably do is to have a little pitch taken out of the starboard impeller to take a wee bit of load off of it and will spin up a bit faster and you may pick up a mile per hour or two.

On my boat the water wheel speedometer will get spun by the wind driving down the road and show some 50 something mph max when my boat on its best day goes 41. Speaking of that, you may want to get under the boat and check the water wheel speedo for debris like grass or anything else that could have gotten in there and would be slowing it down.

What octane gasoline are you running in it?

 

[Dagenham Dave]

I really appreciate all the effort you have put into helping me. I don't really care specifically what top speed I get, I just want to make sure everything is running optimally. It sounds like there's nothing more that I could reasonably do with the engines. It will be interesting to see what happens as things cool down.

When I was checking the front of the impellers, I looked at the speedo wheel. It appeared fine and spun easily. Don't know what gas the previous owners put in, but I topped it up with regular per the manual.

Thank you.

 

[FSH 210 Sport]

You are welcome! I learned most of this stuff from this web page and some by my own experimentation.

Good deal on the fuel. If you can, run gasoline that has no ethanol in it. It you cannot source that fuel then be sure and run Star Tron with each fill up. The next fill up put in enough Star Tron to treat the entire tank.

Depending on how much gas was in the tank and how long it had sat, and whether or not it was ethanol laced, and whether or not the fuel had been treated, that old gas could have an impact on the engines performance. My best advice there is to go out and burn that whole tank of fuel out, I know its a tough task but you can handle it , and refill with fresh unleaded regular. If you are going to put the boat up for the winter start treating the fuel with stabilizer at each fill up and make sure that fuel is run through the engine. At the very least, add stabilizer and fill the tank in prep for storage but make sure that fuel is run through the engine before storage, and fill the tank before storage. Do not top off by clicking the pump to fill it to the top.

Also, if the engine oil that was put in was had to high of a viscosity, E.G. 20W-50 vs 10W-40 that can also have an small impact.

I’m in the same boat as you so to speak, I just want to make sure I get to rated rpm aka rated horsepower or the best it can be at my elevation. I’ve done a fair amount of experimentation with different impeller pitches to get the best compromise since my lakes are from 5000’, 3500’, 1250’ and 500’, the last one I put in my oem impellers. I also use non ethanol fuel if it is available, and I will mix 85 and 91 in the correct proportions to get the 86 octane specified by the manual. I can tell you that when the temperature gets cooler the engines get very perky.

If you have not done so already, get yourself a service manual, it will be very helpful to you going forward and will make regular services the easiest they can be and you will save a lot of $$$ instead of taking it to the dealer. For instance, the first time you do an oil change you will need to buy an evacuator, I have a mighty vac 8L one, and even purchasing the tools, oil and filters will be substantially less than having the dealer service the boat. Depending on where the boat will be stored, winterizing is very easy, do a search here and see what folks are doing. I boat when over night temps are in the teens or single digits and all I do is blow out the mufflers per the manual, and make sure my raw water wash down system is drained as much as possible and thats it.

 

[Dagenham Dave]

Roger that. I will be doing my own maintenance. Thanks again.

 

[Dagenham Dave]

Took the boat out today on a calm River Trent in New Bern NC, air temp the same as yesterday. Don't know what changed, but at WOT port engine was indicating 8000 and starboard 7800. Speed was reading 42 with bumps to 43. VERY HAPPY.

 

[FSH 210 Sport]

Took the boat out today on a calm River Trent in New Bern NC, air temp the same as yesterday. Don't know what changed, but at WOT port engine was indicating 8000 and starboard 7800. Speed was reading 42 with bumps to 43. VERY HAPPY.

Looks like you picked up 100 on the port and 200 on the starboard, if the temperature was the same I’m going to guess the dew point temperature dropped and the barometric pressure increased and gave the engines a bit more O2 and a touch more pressure, and maybe the ECU made some changes. Either way it’s a big win for you!

While there was no apparent increase when you removed the air filters, you may want to invest in a set of RIVA gauze type air filters.

Glad you were able to get things up to rated rpm!