Scoop buzzing
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Scoop buzzing

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    Senior Member californiadreamin's Avatar
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    Default Scoop buzzing

    Anyone use a Dooley style sheet metal scoop on a single carburetor that will start buzzing? My scoop starts resonating so badly at 3k it's startling. Anyone seen this and fixed it? It's doesn't seem to be the scoop mounting as much as the sheet metal flexing at the top with the wind and vibration

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    Quote Originally Posted by californiadreamin View Post
    Anyone use a Dooley style sheet metal scoop on a single carburetor that will start buzzing? My scoop starts resonating so badly at 3k it's startling. Anyone seen this and fixed it? It's doesn't seem to be the scoop mounting as much as the sheet metal flexing at the top with the wind and vibration
    Do you use a gasket between the carburetor and scoop?

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    Senior Member ol guy's Avatar
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    Quote Originally Posted by jimsplace View Post
    Do you use a gasket between the carburetor and scoop?
    And what scoop did you have prior. Also which way was it pointing? M

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    Senior Member californiadreamin's Avatar
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    I do have a gasket between the carb and scoop. No prior scoop, I bought the boat with it and it faces forward

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    Senior Member ol guy's Avatar
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    Quote Originally Posted by californiadreamin View Post
    I do have a gasket between the carb and scoop. No prior scoop, I bought the boat with it and it faces forward
    turn the scoop around and try it. it could be the carb you are hearing. Also is it tight to the carb. I have a dooley single stainless scoop and all I ever hear is the secondaries sing alittle.

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    Senior Member californiadreamin's Avatar
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    It is not the secondaries I'm hearing. This is a severe rattle noise and sounds like the motor is going to spit parts out. I can watch the top sheet metal deflect a good 1/2" and resonate. I know turning the scoop around would likely stop this and I do realize that having the scoop facing forward buys no more performance, I just don't care for the turned backwards look I guess. Thanks for the input, I'll experiment with some things

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    Senior Member jockorace's Avatar
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    Hmmm....I've never heard of this occurring from just front air pressure. One thing I do to the bigger Dooley scoops (2 carbs) is drill two holes about 1" to 1-1/2" in diameter into the bottom rear of the scoop. Stops air from "stacking up" and upsetting the flow thru the carbs. By doing this, you may just change the harmonics of the scoop airflow.
    Stupid question.....but is your engine running clean and smooth? Could possibly be a balance issue or a dead or weak cylinder, dead plug, etc. ??? Jocko

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    Senior Member ol guy's Avatar
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    Quote Originally Posted by jockorace View Post
    Hmmm....I've never heard of this occurring from just front air pressure. One thing I do to the bigger Dooley scoops (2 carbs) is drill two holes about 1" to 1-1/2" in diameter into the bottom rear of the scoop. Stops air from "stacking up" and upsetting the flow thru the carbs. By doing this, you may just change the harmonics of the scoop airflow.
    Stupid question.....but is your engine running clean and smooth? Could possibly be a balance issue or a dead or weak cylinder, dead plug, etc. ??? Jocko
    jocko has a good point. could be engine problem. It would be good to see a picture of the scoop. As I stated I have A Dooley single carb scoop and I would bet It wouldn't flex under a buck(mph). 3000 RPM seems to be a good rpm to show a valve train issue so next question would be, does it do it only on the water or does it do it on the trailer? M

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    Senior Member californiadreamin's Avatar
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    Quote Originally Posted by ol guy View Post
    Quote Originally Posted by jockorace View Post
    Hmmm....I've never heard of this occurring from just front air pressure. One thing I do to the bigger Dooley scoops (2 carbs) is drill two holes about 1" to 1-1/2" in diameter into the bottom rear of the scoop. Stops air from "stacking up" and upsetting the flow thru the carbs. By doing this, you may just change the harmonics of the scoop airflow.
    Stupid question.....but is your engine running clean and smooth? Could possibly be a balance issue or a dead or weak cylinder, dead plug, etc. ??? Jocko
    jocko has a good point. could be engine problem. It would be good to see a picture of the scoop. As I stated I have A Dooley single carb scoop and I would bet It wouldn't flex under a buck(mph). 3000 RPM seems to be a good rpm to show a valve train issue so next question would be, does it do it only on the water or does it do it on the trailer? M
    Good thoughts guys. Here are a couple of pictures. I did consider venting it like you say. The motor does run well, 17" vacuum at 800 rpm idle and very steady no flicker from the needle, motor runs smooth, no indication of a misfire. Balance is a good thought, I can't speak for the balancing, bought this boat in January and have made lots of improvements but haven't been further into the motor than valve covers and intake reseal. I have zero info on the build other than what I have learned through my own research so I can't speak for the balance. I have not revved it up on the trailer and held it at 3k, only snapped it a few times while making adjustments with the hose on it. Definitely no indication of poor running though. It seems to tie into harmonics, if I back off a 100 rpm or speed it up this condition stops. I haven't used this style scoo before so I wasn't sure if it was a common thing or not. Sounds like another one of my wacky problems. A rebuild is in the future but for now I'll run it and see if I can get the scoop to quiet down somehow.

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    Senior Member californiadreamin's Avatar
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    Almost forgot the pictures
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    Senior Member ol guy's Avatar
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    Quote Originally Posted by californiadreamin View Post
    Almost forgot the pictures
    Is that a v-drive or jet and bbc or bbf. ?????

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    Senior Member californiadreamin's Avatar
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    22 DCB BBC I/o
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    Senior Member ol guy's Avatar
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    Quote Originally Posted by californiadreamin View Post
    22 DCB BBC I/o
    Okay with that being said I would check the drive line bearings and if applicable u-joints. A bad drive line will rattle your'e teeth loose. Just to check disconnect the drive and run the rpm up slowly and see what you feel. normally an out of balance engine will rattle at ? rpm and increase as rpm come up. Drivelines will have an area that gets ugly then go away. M As a side note alot of times crap like this only rears its ugly head under power.
    Last edited by ol guy; 05-06-2016 at 07:57 PM. Reason: add-on

  16. #14
    Senior Member californiadreamin's Avatar
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    Good thoughts I haven't noticed a vibration but the scoop may be showing it more than my ass can pick it up

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