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rpm big difference twin engines

Ronald

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Was boating today and noticed 2000 rpm difference in engines. 2014 242 ls...anyone experience this boats brand new..10 hrs or so?
 

Julian

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There might be a few reasons for this, but need a little more info to tell which is most probable....

  1. When was it last run and were the RPMs the same then?
  2. When you say it is different, do you mean the two binnacles are even and the rpms are different, or when you go full throttle one only gets to 6500 while the other hits 8500
  3. Is it the first run of the year after being winterized?
 

Ronald

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1. 3 weeks ago we ran it was off a bit but not this much.
2.yes on the 2 throttles..when even..20k diff in rpm on the tachometer ..full speed both get up to 80k
3. New this year so not winterized
 

Julian

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Ronald

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Thank you im run down and look
 

Ronald

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Looks like the issue..time to do some work. Tx again
 

Julian

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LeeFlan7

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I think i need to do this...about 1000 rpm off with speed being affected
 

Jetster10

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Glad to be of help!

I added this to the FAQ as somehow I missed this! Under Maintenance #34
Julian,

I watched that video as well and did the adjustments as described. But the two RPMs are matched at mid stick but not at full throttle or vice versa. Is it unlikely I would be able to match the throttles throughout the full range. Like if I got the "throttle Sync" mechanism that locks the throttles together. Or should I strive to math them a the range I use the most, like 5500-6500 rpm?
 

Julian

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Julian,

I watched that video as well and did the adjustments as described. But the two RPMs are matched at mid stick but not at full throttle or vice versa. Is it unlikely I would be able to match the throttles throughout the full range. Like if I got the "throttle Sync" mechanism that locks the throttles together. Or should I strive to math them a the range I use the most, like 5500-6500 rpm?
Throttle sync is just a piece of plastic that makes the two throttles move together....I've never understood the need keep the engines closely matched....if they are WAY off, then fix throttle itself. If yours deviate in different spots on the acceleration curve...that is a new issue I've not heard of before.
 

swatski

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Julian,

I watched that video as well and did the adjustments as described. But the two RPMs are matched at mid stick but not at full throttle or vice versa. Is it unlikely I would be able to match the throttles throughout the full range. Like if I got the "throttle Sync" mechanism that locks the throttles together. Or should I strive to math them a the range I use the most, like 5500-6500 rpm?
The only way to do this is electronically, with the Ridesteady/Hydrophase cruise control. It synchs the engines across the RPM range - bypassing the throttle cables - direct to APSs (accelerator position sensors).
It costs over 1k, but it is worth every penny in that boat.
I love my engines humming in synch, it drives me ape-shit if they are off.
However, if your drivetrain is tuned perfectly well, at WOT your port RPM will be about 100 higher due to uneven pump loading.

--
 

zipper

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I have mechanical throttles, no electronic interface. I also have Throttle Sync, my wife bought it last year thinking it would help her drive with twin throttles...we/I never use it. Locked together, starboard will run higher rpms than port maybe 300 rpm. once out of no-wake I always run with the port throttle slightly ahead of starboard to gain harmonious synchronization and match the tach readings. I have been wanting to adjust the throttle stops, but I too do not think it is linear either. Wish mine was a candidate for Ridesteady. It really frustrates Willow, being a small handed southpaw, not being able to use throttle sync because I cannot listen to my engines run out of sync. I said frustrates...but it really pisses her off.
 
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Billtex2000

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Agree...I did the adjustments and mine are off by 500 rpm, BUT, they are in "harmonious synchronization" (well put @zipper). I still think that my port tachometer is off. Throttles are aligned at WOT, full forward, but the port tach is 500 revs behind the starboard. Here's my pic of WOT last week...light breeze, 2 on board and a little over a 1/4 tank. The bottom is dirty from wet slipping all season. Gps said 38mph. Port engine is 500rpm lower than starboard according to the tach, but the engines sound like they are in sync.tach.jpg
 

zipper

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@Billtex2000 Would it be possible to swap tacks/wiring temporarily between them to verify if one is bad or not? Might help isolate the issue.
 

Evildwarf

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The Throttle sync product will not fix the out of sync RPM issue.
With the mechanical throttles you may still have "throttle drop" on one or both engines even after you have adjusted the throttle cables correctly. Throttle drop can be as much as 500 to 800 RPM on my boat at times with the result of having the motors "out of tune" with each other. It doesn't effect steering but the sound of the out of tune motors is unpleasant.
The RPM difference in the motors is independent of throttle position....really only a problem if you are sensitive to the sound of the motors out of tune. It can be a pain to tune the motors sometimes due to throttle drop but they sound so good when they are in tune
 

Stevenpigsooie

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On a 2016 AR240 I've never adjusted the throttle cables and with throttle sync I have about a 400 rpm difference in no wake mode, nearly identical rpm in the 4,500-5,550 range, and then again about a 300 rpm difference at WOT. No idea why there are differences or if it even matters. I can't remember which engine runs higher but will pay closer attention next time, but I think it is port side.
 

Ronnie

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On the previous generation of boats (2014? and older) the impellers have different pitches with the basic rationale of one theory as i understand it, being that one side is less efficient than the other at taking in and therefore pumping out water due to the way the intake is positioned on the V hull and because both impellers spin in the same direction, the different pitches of impellers rebalance the performace of each pump so that the boat tracks straight when underway, the cost is a small difference in rpm between the engines.

Now the boats come with pitch matched impellers which from what ive read here causes a small difference in engine rpms. I wonder if yamaha determined that their articulating keels enhance the tracking enough that (the cost of) differently pitched impellers are no longer necessary?

That stated, my throttles are not perfectly synched but the 200 to 300 rpm difference is easy to equalize even with the throttle synch engaged (only used by other pilots/drivers) and most of the time :it doesnt bother me enough to take the few seconds it takes to make the adjustment. That is, its close enough, for me anyway.
 

Billtex2000

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@zipper If I still see the difference in the spring after oil and plug changes, I'll try switching the tach wires. Good idea!
 

Seadeals

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Here is my split.
IMG_0248.JPG
It has been that way for years and identical after a port impeller refurb. I did not trick my port engine into running 8750 rpm. Its ECM logged only 1.69 hours in the 8000-10000 range over 284 hours and the starboard 1.78 hours in 286.4.
IMG_1804.JPG
I run at WOT a lot. What that tells me is the tachs are poor reporters of actual rpm which is also discernible from the audible sync sound. As for designed pump loading being the culprit (at least old boats) we would have to point our noses more to damage/condition of impeller as my split is the OPPOSITE of @Billtex2000 and mine didn't change after a needed refurb (the ECM limits the top rpm).
 

Billtex2000

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I agree @Seadeals ! I don't have much faith in the tachs. I think our numbers in the 8000-8500 range are more believable at WOT, and my port tach is just lagging, because they devinitely SOUND in sync. My feeling is that both my engines are running at about my 8500 number, but damn, where are you getting that speed from!!!! Did you GPS that number? I haven't seen 41-42 in years. Around 38mph is the best I can muster in ideal conditions. I'd better get my hull cleaned and waxed, and a good tune up and pump/impeler check in the spring! It's still just so annoying seeing those needles not lining up!!! LOL
 
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