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I’ve recently acquired a Holley model 3246. I had to go to Holley for ID since it didn’t show up on their ID charts. They tell me the 3246 is a “rare” (their words) 780 CFM that came stock on ’66 396 and 427s. It is a 4150 with duel feed, mechanical secondaries, and a single pump. I’m hoping to modify the carb for a blower by changing the power valve reference point to the intake.

Looking this carb set-up over, it seems to me that mechanical secondaries with a single accelerator pump is a recipe for fuel starvation when you mash it off the line. I understand that it’s possible to modify the linkage to synchronize the primary and secondaries to open at the same time. Would I be better off trying this and going with a 50 cc pump? I’m guessing that since I don’t see this modification much that it is either not and easy modification to complete/tune or there is other serious downsides to synching them.

If someone out there has done this, can you give me some feedback on your experience and what is involved with it.

Thanks
 

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Double pumper without the second pump? Sounds like you have a vacuum secondary carb, all 780cfm Holleys are vacuum secondaries as far as I know.

Can you post a pic?
 

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4 Jaw is right. You have a vacuum secondary. It may be missing the vacuum cannister. The 780s are 4150s. That means that they have a secondary metering block. 4150 does not mean double pumper.

I would not waste my time modifying this carb. Keeping it original will also hold it's value. Put it on Ebay as an original equipment carb and it you may get over $200 for it. Depending on the condition it could go as high as $300 to $500. Just make sure you know exactly what it came on, and what the date code is.

The money you get by selling this carb will help put a real blower carb within a more palatable price range.
 

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Discussion Starter #4
I was sure I would get this resonse about all the 780's being vacuum secondaries. Actually, I found the same info in a couple rebuild books I've read lately - that Holley never made a mechanical secondary 780. Now I'm not saying this carb was not converted in it's lifetime, but it's definitely mecanical linkage. I'll snap a few pics and post them in a couple hours. Maybe someone can figure it out with some "visual aids".
 

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lluciano77 said:
If it has that gear drive conversion kit, you should get rid of it. They were an extremely poorly concieved idea.
...thats for sure, seen a few secondary linkages with a bolt in the slot too.:nono:
 

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Discussion Starter #7
Now that I see how the linkage is working, I think you all are right. It's a mechanical secondary, and aparently converted. Attached are a few pics that I just took. As you can see, the choke is gone, as well as most of the mechanism associated with the it.
 

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Where is the squirter nozzle located on that carb? Could it be a center squirter, located between the primary and seconday side with four holes? It then wouldn't need the secondary pump. I haven't seen linkage like that before that I can think of.
 

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It is not a center squirter. That is a vacuum carb converted to a mechanical linkage.

Try to find a donor 1850 carb or get the secondary linkage arm and secondary cannister.

No matter how you tune that carb it will always bog when the secondaries kick in.
 

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YIKES!:eek:
 

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Discussion Starter #13
HA! Isn't it funny how a good deal on a carb can turn in to a realy bad deal on a paperweight in 10 posts or less! I knew I should have been suspicious when I bought this out of the trunk of a Honda. Just the nature of the beast when buying old rod parts, sometimes your the windsheild and sometimes your the bug.

Thanks for all the help guys.
- Stan
 

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I don't think I would go as far as to say it's junk. Looks as if someone was saving money. On a circle track or drag car you don't need the extra accell. pump when launching at WOT. Bad for a street ride though.
 
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