Low and Uneven RPM's (not spark plugs)

[Thomas Smith]

I just got back from a trip, found my PORT engine topping out at 7000 RPM's and the Starboard 7500. Both ran great both fired right up both have had higher rpms last trip out (8000). YES I changed the plugs, I have owned the boat since new (2006) and I know that plugs are always the first step. This plug change did not help, I also checked the clean outs and viewed under the boat and no debris. Like I said I have owned the boat since new and have never had an RPM issue that wasn't fixed by the spark plugs. Curious if there is any other tricks of common issues. I also am not aware of any sort of impeller strike that would affect performance. I did not check air cleaners yet but every year find those to be spotless and never have been an issue over the past 18 years.

Thanks for the help.

Shane

 

[lazergeek]

Heat and Humidity would account for the decrease your seeing. What Altitude are you boating? Did you change lakes with a diffrent altitude? Impeller and wear ring damage would increase RPM's not decrease.

 

[Scottintexas]

Both engines having an issue makes me think fuel

We’ve had members in the past have to do two plug changes even though they swear they were new and gapped correctly

 

[FSH 210 Sport]

I just got back from a trip, found my PORT engine topping out at 7000 RPM's and the Starboard 7500. Both ran great both fired right up both have had higher rpms last trip out (8000). YES I changed the plugs, I have owned the boat since new (2006) and I know that plugs are always the first step. This plug change did not help, I also checked the clean outs and viewed under the boat and no debris. Like I said I have owned the boat since new and have never had an RPM issue that wasn't fixed by the spark plugs. Curious if there is any other tricks of common issues. I also am not aware of any sort of impeller strike that would affect performance. I did not check air cleaners yet but every year find those to be spotless and never have been an issue over the past 18 years.

Thanks for the help.

Shane

I agree with @lazergeek and @Scottintexas

So you have the MR-1 engines in your boat correct? Aren’t those engines supposed to spin 10,000 rpm?

Your air filters are the original ones that came with the boat ? Next time out, pull the air filters and make sure there is no debris in and around the air box, leave them out and make a test run and see what the results are.

Also, where did you get the spark plugs? There are a lot of china made fake NGK plugs, you can go to NGKs website and there is a page that will show you how to identify fake NGK plugs. There was a thread on that here.

Thread 'Fake NGK spark plugs out there??'

Feb 12, 2020

Ok, I get fake sunglasses, clothing, etc., but why am I surprised that they'd fake sparkplugs??
Saw something on a Honda Pilot forum today and looked into it - apparently a common thing on Amazon... So much so that NGK has a '5 step guide' on how to spot the difference.
A 5-step-guide on how to distinguish fake spark plugs
Some reports on line source the plugs as from Amazon, eBay (yeah, that one I'd expect!), AliExpress (likewise), and a retail store (that's a surprise IMO). [Counterfeit Ngk Spark Plugs | Consumer Alert]
Good pictures here of real and fake: WARNING –...

• msavold
• Replies: 5
• Forum: General Discussion

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[Scottintexas]

I believe his 2006 sx210 has the non-ho 110 hp engines that top out at 8k rpm

 

[Thomas Smith]

Heat and Humidity would account for the decrease your seeing. What Altitude are you boating? Did you change lakes with a diffrent altitude? Impeller and wear ring damage would increase RPM's not decrease.

Thank you and actually I did change lakes, I normally boat at or near sea level and this trip I was at 5000 feet. Would this elevation create this symptom? Thank you for the information.

 

[Thomas Smith]

all great information and thank you, I will start troubleshooting as soon as I can. I am almost positive my NGK's came from Amazon soooooooo there's that, again thank you all!

 

[FSH 210 Sport]

Thank you and actually I did change lakes, I normally boat at or near sea level and this trip I was at 5000 feet. Would this elevation create this symptom? Thank you for the information.

YES.

Depending on temp and humidity the density altitude could have been 6000-7000’ which will have a dramatic impact on power output and rpm’s, you could easily lose 1000 rpm’s or more.

What was the temperature when you were at 5000’?

Now that you are back home take your boat out and try it, I bet you will find everything is normal, no need to continue trouble shooting.

 

[lazergeek]

Thank you and actually I did change lakes, I normally boat at or near sea level and this trip I was at 5000 feet. Would this elevation create this symptom? Thank you for the information.

5000 feet elevation would 100% be your issue here. The only way to get all your RPM's back if your intending on staying at that elevation is to repitch your impellers for that altitude.

 

[Thomas Smith]

Interesting! It was mid 90's to upper 90's and I never even thought of the density altitude component. Thank you all, and I will hopefully get the boat out this weekend and confirm it. Again Thank you !