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Twin Honda 40s rpms low and off

 
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markm



Joined: 09 Jan 2020
Posts: 6
City/Region: Clinton
State or Province: WA
C-Dory Year: 2006
C-Dory Model: 22 Cruiser
Vessel Name: Otter
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PostPosted: Mon May 25, 2020 9:14 pm    Post subject: Twin Honda 40s rpms low and off Reply with quote

https://youtu.be/EK22Zswllfg

This weekend Michelle and I did a trip to bowman around Whidbey. 2 people lightly loaded full fuel and water. As you can see in the video the Hondaís vary in RPM greatly and low. However we traveled mainly at 18kph and had decent fuel burn. I estimate we used about 30 gal in just under 7 hours of run time. A little bit about the boat. It has been sitting for many years and recently just had the motors all serviced including impellers thermostats etc.
Things Iím asking
Does the variance in rpm matter?
Does running lower than Honda says matter?
If things need to change I am assuming start with props is this correct?
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hardee



Joined: 30 Oct 2006
Posts: 10886
City/Region: Sequim
State or Province: WA
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Sleepy-C
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PostPosted: Tue May 26, 2020 1:44 am    Post subject: Reply with quote

Mark, I doubt that Honda throttle controls are calibrated to be perfectly matched side to side. (My Yami's have a bit of difference -- but not that much.) I'm thinking you need a prop change as your WOT RPM's, (Wide Open Throttle), are not getting up into the acceptable range (Guessing here, but 5500 =/-) is more like what it should be. Check your Owner's manual or mfg website, and find out what that should be. Then Check your props and see what they are and adjust to get your RPM into the acceptable range.

If you are not getting up into the recommended range, you are lugging the engine. Probably not good over the long haul.

Glad you got out and got a ride, can't be all bad.

Harvey
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Blue Rose



Joined: 17 Sep 2012
Posts: 67
City/Region: Montgomery
State or Province: MN
C-Dory Year: 2006
C-Dory Model: 22 Cruiser
Vessel Name: Blue Rose
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PostPosted: Tue May 26, 2020 10:09 am    Post subject: Reply with quote

Mark-
I also have Honda 40 twins on my 22. I am not as concerned about the difference in the tach readings as I am that the WOT RPMs are too low. I can't tell from the video if the engines are lugging or just not throttled all the way up. My first check would be the linkage adjustment settings at the carburetors to make sure all of the throttle plates are full open when the throttles pushed to WOT.

With a medium load on board, my WOT is about 27mph at 5800 rpms with 3-blade 11 1/8 x 13p aluminum props. Normal cruise for me is about 18mph at 4200rpms and 3.5mpg.

My honda tachs do not read reliably. Sometimes one tach erroneously reads more than 1000rpms higher than other when I can hear the engines are running the same. I tap on the glass and then the needle will drop back down to match the engine speed.

Its not a problem if the engines are not "exactly" the same rpms or throttle setting. I tweak the throttles settings until I hear both engines are running happy and the harmonic resonance is gone.
Jim

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Blue Rose



Joined: 17 Sep 2012
Posts: 67
City/Region: Montgomery
State or Province: MN
C-Dory Year: 2006
C-Dory Model: 22 Cruiser
Vessel Name: Blue Rose
Photos: Blue Rose
PostPosted: Tue May 26, 2020 10:38 am    Post subject: Reply with quote

Was also going to add that if the linkage settings and prop size are ok.... My 2nd check would be fuel related since the boat was not used for a long time.

The honda 40 carbs clog very easily. Were the float bowls drained before putting the boat into storage? Did you drain the old gas before putting new gas in the tanks?
Jim
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