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Discussion Starter #1
my carb got stolen. was a 750 dp holley.could i use a 750 vac. sec. holley on a jet boat.350 chev jacuzzi yj.
 

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and it worked well? my neibor said never use a vac sec carb on a jet boat. so hes full of s**t?
He's not full of it, as it will work fine.
Is it base case......Hell no!!
A single carb can be bad enough with cyl to cyl fuel distribution (especialy part throttle cruising), let alone a vac sec, they make a real mess!! :)sphss
 

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mo balls than $cents$
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seen to many detonation damaged pistons to ever run a vaccum secondary on anything i own:)bulb
 

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I have run a 3310 750 Holley vac secondary on my 454 BBC. My buddy gave me his 750 DP, but I could never get it to idle right. Neither could he because he replaced it with a Demon. My vac second. has been running flawless, so I don't have really any good reason to take it off. Plus I just rebuilt it too. I am not expert, but I think you should be fine running a vac sec on your 350.
 

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I stay away from vacuum secondaries because they are 1, bad on gas mileage, 2 I like to control the throttle position of my boat, 3 distribution issues. Many people use them with good results though so its all personal decision I suppose.

~Brian
 

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Discussion Starter #9
thanks for all the info guys.im a pretty good carb guy,but never tried a vac.sec. on a jet boat.what jets and power valve would you suggest as a baseline? 350 chev 11:1 compression, 488I 510E 300i 310E 110LC CAM,B impeller 1400lb boat. thanks scott
 

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The only time I tried to run one. The secondarys would try to open up just at plane then you would try to back off and the boat would come down from cruise and off plane! It would run good at WOT. Just didn't like the surging when secondarys opened!
 

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...Just didn't like the surging when secondarys opened!
That's because you didn't have the right springs.:)sphss
715 vac Holley on my 468 Cheby to 5200 RPM's...works great, I need nothing bigger w/better fuel economy vs a double pumper.
 

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why would you want to put a vac carb on over a mechanical double pumper i would rather trust a mechanical arm over a bladder and a spring opening my butterflies any day plus there is no such thing as good gas mileage for a jet boat until that is when i come out with my new hybrid.:)hand
 

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why would you want to put a vac carb on over a mechanical double pumper i would rather trust a mechanical arm over a bladder and a spring opening my butterflies any day plus there is no such thing as good gas mileage for a jet boat until that is when i come out with my new hybrid.:)hand
"gas mileage" no, better "fuel economy" yes, as the vacuum secondarys on a properly set up carb only open when the engine needs it.
As far as "dependability" well, 9 years running and never any issues.;)

*It's funny seeing engines with waaaay too big carbs on them because the owner thinks "bigger is always better".:D
 

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*It's funny seeing engines with waaaay too big carbs on them because the owner thinks "bigger is always better".:D
So true:)devil You Know you gotta have 1700cfm of carb for an engine that requires 725cfm:|err
 

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E-7 Sheepdog (ret)
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The Vac Secc. will run just fine, although IMO, a 750 is way too big for a 350.

Set it up box stock before you go to jacking with it.

Surging on a vac. sec. is a definite sign of the wrong springs in the sec. diaphram, most likely too LIGHT.
If they are set up properly, you will never know when the sec's open, unless you are watching them.
 

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Discussion Starter #20
THANKS EVERYONE.just had a spare carb in the garage and didnt want to spend 500+ bones on a new double pump right now.would rather spend it on gas at the river.
 
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