Low rpms please help!

[Rob2021]

Hello, I would like to start this thread off by saying that I am a knew member and appreciate any help that I can get! I know that there are a few forms out there regarding low rpms at full throttle but none of them seemed to be exactly like my issue. I have a 2015 Yamaha 212ss with less than 150 hours on it. At full throttle my port engine maxes out at around 6,500 rpms and my starboard engine maxes out at around 7,000 rpms. I reach a top speed in the low 40 mph range. The rpms for both engines are in sink until I run them at full throttle. When I flush out the boat, the engines sound noticeably different from each other. I believe that these engines are supposed to max out at 7,500 or 8,000 rpms (either way I am clearly not hitting that) and the boat should have a top speed at around 51 mph. I already replaced the spark plugs and am wondering what I should try next. Any help is greatly appreciated!

 

[HangOutdoors]

@Rob2021 A couple of quick things you can check, is the oil level and the air filter. Make sure that the oil isn't overfilled. These engines are sensitive to oil level. Check warm and level. Then check and see if air filters have oil in them or are very dirty/clogged. This is a good place to start and you can begin eliminating easy things right away. Then we can go from there. You may have something a miss somewhere else but this is a start.

Also when you replaced spark plugs did you personally check the gap on them? I know they are pregapped, but I found a couple that were out of spec from the manufacturer.

 

[Rob2021]

@Rob2021 A couple of quick things you can check, is the oil level and the air filter. Make sure that the oil isn't overfilled. These engines are sensitive to oil level. Check warm and level. Then check and see if air filters have oil in them or are very dirty/clogged. This is a good place to start and you can begin eliminating easy things right away. Then we can go from there.

Thank you! I will check the air filters ASAP and check back in here as soon as I do.

 

[HangOutdoors]

After that I would probably be looking at the condition of the impellers and the sealant in the pump. Initially get a flashlight up in there and look around and snap some pictures. At 150 hours there could be some wear or other issues.

 

[tdonoughue]

You will also want to check your throttle adjustments back on the walls in the engine compartment. See https://jetboaters.net/faq/#faq-24

Welcome!

 

[Canuckjetboater]

As usual on this form insightful answers. Spark, fuel, air, throttles....great places to start.

 

[grywlfbg]

@HangOutdoors gave some great advice. But to add some color to the oil suggestion, these motors like to be filled to the halfway mark on the dipstick, not all the way full. You will lose rpms with the oil at the Full mark.

 

[HangOutdoors]

@grywlfbg Actually, at least on my engines, you can find another thread here where I did some real testing with posted results, the engines runs rpm's optimally when it is halfway between the mid point and low mark. But that has to be a personal choice and comfort zone where people decide to run their own oil level.

 

[HangOutdoors]

Here is a thread with much discussion and my personal results with oil level and the processes I went through.

https://jetboaters.net/threads/10-hour-oil-change-speed-decrease.26812/page-6

 

[Rob2021]

It was the air filters! I just took them out and now I’m getting around 7,500 rpms on each engine and I’m hitting 52 mph.

Just out of curiosity, do these engines top out at 7,500 rpms? Also should I put new air filers in or just run without them?

Thank you all so much for the help!

 

[Rob2021]

Also this is what my air filters looked like... long overdue!

 

[HangOutdoors]

Put new air filters in. Also please check the oil if you haven't, for quality and fill level. If it doesn't look clean, change it with the oil filters. If you properly maintain those engines they will last for a long, long time.