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Discussion Starter · #1 ·
Anyone have any expirence or first han knowledge of this rig , maybe own one or a buddy with one ? This boat (in our shop for work)was produced with a late Kodiak SBC roller setup with a set back AT Customer lives at high altitude and says the boat is pretty "anemic" Tom


 

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Discussion Starter · #8 ·
balance that carb & you'll get 15mph. :)sphss
David (jdf) , Thanks you folks are the best !!

Doc, Were going to weld the chain into a steering wheel for Day "cruisin"

Zombie thats the "segway" the boats here for "rehab" ;) Very few out here that love a bad ass "Smally" more than me , Sons got one thats a "beast" but Not the Mill for a full grown day cruiser agreed

and Vintage ... where does one get a carb "balanced , pray tell;) I smell a tech article

the BBC is ready to swap ,this boat should go back to NM later next week , the owners are hangin' in Cali till its done !

 

· About 500' AGL
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Hey Tom....will the new Big Block be running a mechanical or vacuum secondary carb.....I'm just curious to know what the norm is on a 21 Jet. My brothers boat has a Vacuum secondary on his and I think it might be hurting his performance a little.
 

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Hey Tom....will the new Big Block be running a mechanical or vacuum secondary carb.....I'm just curious to know what the norm is on a 21 Jet. My brothers boat has a Vacuum secondary on his and I think it might be hurting his performance a little.
Not to hijack, but when Jim Guthrie switched out my vacuum secondary 750 for a mech secondary 750, he told me you should always run mech secondaries on a jet boat motor. Reason he gave me was "you want the secondaries to kick in as soon as possible if you hammer the throttle, not wait for the vacuum to build up to open the secondaries." I've noticed a considerable gain outta the hole w/ the mech secondaries carb.
 

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Discussion Starter · #13 ·
Hey Tom....will the new Big Block be running a mechanical or vacuum secondary carb.....I'm just curious to know what the norm is on a 21 Jet. My brothers boat has a Vacuum secondary on his and I think it might be hurting his performance a little.
MP we realized today (after working the carb numbers) that the "existing Carb" (pictured) just wont do plus its "non adjustable soooo. plan B is to upgrade him to 750 or better , possibly a Marine DF/DP Most everything else is a "bolt up from the small block , some of the brackets even have "dual patterns"
Plan B is to upgrade him to 750 or better , possibly a DF/DP ,I'm personally not a huge fan of vacum secondaries, alot depends on the customers budget and what he wants as well . I do know he's at high altitude so we want to "compensate" as best we can, Time will tell he and family are boppin around in Nor Cal (SF area) seeing the sights We'll know more this week Tom

personally I'd opt for a 950 hp but this boat needs a "marine carb" due to the covered engine

River dad Where the pic ??
 

· About 500' AGL
Joined
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2,239 Posts
Not to hijack, but when Jim Guthrie switched out my vacuum secondary 750 for a mech secondary 750, he told me you should always run mech secondaries on a jet boat motor. Reason he gave me was "you want the secondaries to kick in as soon as possible if you hammer the throttle, not wait for the vacuum to build up to open the secondaries." I've noticed a considerable gain outta the hole w/ the mech secondaries carb.
MP we realized today (after working the carb numbers) that the "existing Carb" (pictured) just wont do plus its "non adjustable soooo. plan B is to upgrade him to 750 or better , possibly a Marine DF/DP Most everything else is a "bolt up from the small block , some of the brackets even have "dual patterns"
Plan B is to upgrade him to 750 or better , possibly a DF/DP ,I'm personally not a huge fan of vacum secondaries, alot depends on the customers budget and what he wants as well . I do know he's at high altitude so we want to "compensate" as best we can, Time will tell he and family are boppin around in Nor Cal (SF area) seeing the sights We'll know more this week Tom

personally I'd opt for a 950 hp but this boat needs a "marine carb" due to the covered engine

River dad Where the pic ??
Thanks....his has a Demon 650 Vacuum Secondary on a Marine Power 454. It is shit out of the whole and has a lag that you can feel until the secondaries open. I'm thinking of changing it out to a 750 DP and see what it does.
 

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Discussion Starter · #20 ·
Thanks....his has a Demon 650 Vacuum Secondary on a Marine Power 454. It is shit out of the whole and has a lag that you can feel until the secondaries open. I'm thinking of changing it out to a 750 DP and see what it does.

MY 02 Even if the Marine power motor has the small OEM heads 6 fitty is under carburated I would go 750 or better and give it plenty of fuel supply I dont belive the Carter pump supplied with that motor is sufficiant We will check pressure and volume on this "project" and make a decision Tom

BTW the owner has some pretty accurate numbers on this particular boat from past experience ,it will be interesting to see the Comparisons
 
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