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Vibration at Idle (Twins) On for 3 off for 3 seconds

Old 08-15-2018, 09:47 AM
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Default Vibration at Idle (Twins) On for 3 off for 3 seconds

Vibration at Idle (Twins) On for 3 off for 3 seconds. Doesnt show up at other RPMS. Make the no wake zones miserable. Any way to chase the issue down before dissassebly? Thanks

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Old 08-15-2018, 09:59 AM
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What kind of boat?
Reason I ask: I've seen some boats like Fountains and NorTechs that have swim platforms that are "enclosed" when at idle, "burp" exhaust pressure out once it builds up enough pressure to lift the aft end of the boat and vibrate out.

If the above does not apply, have you narrowed it down to which side has an issue?
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Old 08-15-2018, 10:32 AM
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Originally Posted by Sydwayz View Post
What kind of boat?
Reason I ask: I've seen some boats like Fountains and NorTechs that have swim platforms that are "enclosed" when at idle, "burp" exhaust pressure out once it builds up enough pressure to lift the aft end of the boat and vibrate out.

If the above does not apply, have you narrowed it down to which side has an issue?
So their farting............
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Old 08-15-2018, 10:56 AM
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Originally Posted by F-2 Speedy View Post
So their farting............
Pretty much.
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Old 08-15-2018, 11:42 AM
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Originally Posted by Sydwayz View Post
What kind of boat?
Reason I ask: I've seen some boats like Fountains and NorTechs that have swim platforms that are "enclosed" when at idle, "burp" exhaust pressure out once it builds up enough pressure to lift the aft end of the boat and vibrate out.

If the above does not apply, have you narrowed it down to which side has an issue?
From another thread:
Originally Posted by cyrus77 View Post
Yes I know this sport is not cheap but.....
I burned 110 Gallons at $3.33 per gallon here in California last weekend in my 33 Scarab AVS with Modded 502 MPI 530 HP a side. I
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Old 08-15-2018, 12:18 PM
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Sydwayz most likely hit it. It was/is an issue for some 33s when you get away from Black engines
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Old 08-15-2018, 12:25 PM
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Originally Posted by scarabman View Post
Sydwayz most likely hit it. It was/is an issue for some 33s when you get away from Black engines
Well, black engines typically have the cast iron manifolds and are heavier in the tail; whereas the blue engines typically have more aluminum and SS.
The 33 AVS DOES have the right 'kind' of trapping swim platform that could cause this.
My suggestion to see if this IS the issue, is idle along side of someone else, and see if they can see they can see the "burp" happen. Having someone lay down back over the swim platform may throw off the weight balance which may affect this "timing" (good or bad).
Idle beside a friend, and have a thumbs up/thumbs down hand signal; depicting to your friend in the other boat, when the vibration is on/off; and see if someone outside the boat looking at the rear can correlate.

Dropping the tabs all the way down at idle may raise the aft end up, enough to keep the air pocket from forming. Same goes with also/either tucking the drives ALL the way in to the transom.
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Old 08-15-2018, 11:20 PM
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hmm. yes enclosed tail. I have stainless marine manifolds and pips
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