Technical Holley vacuum secondary mechanical link

Hi All. I just picked up a Holley List #3607 vac secondary carb. Mid 60's Chevy stuff. It has a secondary link that makes it completely mechanical added by someone sometime (A long time ago). There are washers under the secondary diaphragm cover to leave an air gap so it could move freely. I've heard about putting a small machine screw through the slot in the secondary arm to help it open earlier but this was set up to open the secondaries fully all by itself and it looks like a manufactured part. Does that work, or does it just make a loud backfire when you mash it?

 

Looks like an old aftermarket gizmo to me.... Pretty cool though.....

 

if you move the throttle and it opens the secondaries, then yes, it works to open the throttle. Whether or not it makes a backfire when you mash the throttle depends on a lot of variables about the engine and car, and you didn't tell us anything about them, so we can only guess.

 

If the carb has the correct spring in the diaphragm there is no need for the other stuff. A Holley trick kit is what you need. I have run a vacuum carb with a bolt in the slot. It makes the carb act like a mechanical double pumper. Moving the bolt around in the slot gives you different opening points on the secondary blades. Some experimentation is needed. I had good success with it. Your asking the carb to do something it wasn't designed for. If you don't want to try to fool around with it then get the correct carb for your application. It just takes some time and some driving to get it right.

 

Yep, what he ^^^ said. Many a vac secondary's got the old screw in the slot trick.

 

I think what your looking at years ago was called a 1 to 1 kit . When the primaries moved the secondaries moved the same amount . That is how the term 1 to 1 came into play . Can you show a photo down int the top of the air horn of the carb ? I had 429 SCJ that had a 1 to 1 center squirter on it at one time , not a very street-able carb at all .

 

The 1:1 part I'm familiar with is a simple bent wire gizmo, but that was to change a progressive mechanical secondary carb to 1:1, primary:secondary. Circle track racers used them to avoid the sudden "hit" of secondaries opening quickly when they actually started to open at ~ half throttle. They wanted a smooth transition, especially on dry slick tracks.

This may or may not be of interest or apply to your question.....probably not.

Lynn

 

You don’t have an accelerator pump on the back two and a mechanical secondary! You will go boom when you hit the gas!





Bones

 

Drive with an educated foot.

 

This may not matter much to you but look to see if the number 3890497 accompanies the 3607 list number.
If so, that is a pretty rare oem Holley for the 67 Chevelle 327/325 hp (l79) engine, this number is specifically for the California AIR cars (smog legal).

 

Really James!! My foot is dumber than a box of rocks! Only knows one thing.....WOT! Lol






Bones

 

Eelco used to make a kit to convert a vacuum secondary to mechanical. But they used two quarter moon gears on the right side throttle shafts. You did away with the vacuum pod. It had a squirter that stacked on top of the front squirter and the tubes reached back into the secondary throats. So it was like a double pumper but only using the front accelerator pump for all four butterfly's. You cant just make a vac secondary work at one to one unless you have the fuel to cover the dead spot. Would have worked better with a 50cc pump, but it worked ok. The big 50cc pump was not available when the Eelco kit came out. Lippy

 

Look at that last pic close. That is not a true one to one. That front linkage piece moves quite a ways before it begins to open the secondaries. It has to contact the pin on that arm before it does anything, probably a quarter throttle or better. Lippy

 

Been fun but I'm done. Lippy

 

That parts real name is a "waste of time". Why try to make a DP from a Vacuum secondary carb? They are two different things for two different purposes. There must be thousands of them lying around unused. Even 8000 miles away, here in New Zealand we can find a double pumper if that is what we need. I would venture to say that very few street cars could use a double pumper effectively. Even less of them actually NEED one.

 

Ok, how's about some pictures of those please..... I'd love to see them... Thanks!

 

James, I don't recall ever seeing a race-car with "Tuned by Educated Foot" on the front fender...

 

If you're talking to me , since Photobucket got greedy , I don't know how to post pictures here from my tablet , if someone is willing to explain how to do that , I'd be more than happy to share that , if you do Facebook , go to the NTBA site , I can do pics there ,or go to the tbucketeer.com site , I have pictures there ..#

 

If you're gonna run " race type" stuff on the street , you better have an educated foot.

 

Kinda hard for me to live that one down.

 

Do you the List # on those carbs???? I'll just look those up on the Holley site... Thanks!

 

Holley 9776 ..

 

Unless you have a lot of engine it's called to much carburetor to early without the aid of the accelerator pump. But it does look like this one is progressive.

 

Thanks!...
Here's what they look like..... I would love to take one apart to see how the hell this thing works!...
Sorry for the double pics....

 

I just got the carb. No car. Originally it would have been on a '66 327 Chevelle as far as I can tell. The aftermarket secondary link was added by someone along the way. I don't think they used it very long cause it's hardly worn. I'm used to engines backfiring or lots of hesitation if you pop open the throttle bores with no squirt from lean out, or you buy a double pumper if you want it all open right now. Just wondering if anyone had seen or used something like this and how well it worked. Or not. I can't imagine it working well on a vacuum secondary carb. I'm going to put the correct link on it and use the carb on my 283 for a while. See if it likes it.

It's all interesting. This one was set to start opening the secondaries at about half throttle. I think it would be good to use on a mechanical secondary carb if you wanted to adjust when the secondaries opened for a better transition, like you said.

It does have that number right above the List number. Date code is 504. (1965, Oct, 4th week)

Thanks for all the info. . .
Dave

 

When the Eelco kit came out, there were no double pumpers. Lippy

 

Yep! That’s going to haunt you! I never noticed no educated foot on you at the drag strip! The way you were running I though you might have some toes hanging in the carburetor! Lol



But I did know what you meant. I have to use an educated foot every time I start my wagon! Bones




Bones

 

The only difference between these any a vac sec carb is the way the secondaries are opened , no magic !

 

Right, but with vacuum secondary’s they won’t open till the engine needs it and the can be tuned with different springs and it opens slowly so that an accelerator pump is not necessary. Very streetable, especially for a mild engine and someone that has a heavy foot.






Bones