I have a Holley 3310 Vacuum Secondary carb (750 w/850 square bore base plate and worked over main body)

Is there a way I can convert the Vacuum Secondary Linkage to a Mechanical Linkage without having to remove the entire secondary throttle shaft?

The Vacuum setup just doesn't seem to be opening fast enough...

I've already replaced the Diaphram in the Dashpot and installed the lightest spring (white), but it still doesn't seem to be opening up

The Diaphram held pressure while it was off and the vacuum port wasn't blocked or anything....

And no, I didn't forget to install the new gasket between the Dashpot and the main body

Anyhoo, I was just wondering if they made an easy conversion kit or sumthin....




Rick

Aztek T/A WS7 & 70 RAM AIR IV T/A
Moderator @ LS1, FAST LS1, FUEL ****,
The F-Body Hideout & ChopperForums

 

If you want to make sure the seconday is opening, make a simple tester as described in my post in this thread:

http://web.camaross.com/forums/showt...ight=cardboard

 

cannot convert a vacuum carb to mechanical, vacuum does not have the secondary discharge nozzle feed or the ability to have one, and if you tried to convert it all you would get when you mashed the pedal would be blown power valves and caught on fire air filters

 

Actually, I spoke with a Holley Tech yesterday and he said there is a mechanical conversion kit with an adjustible spring loaded linkage that delays the opening speed of the secondaries so there's no need for a secondary accelerator pump, but Holley doesn't make it and the company that did, went out of business years ago

So off to Ebay I go...


Rick

 

Hehe

I actually used a wireless mini cam and mounted it to the edge of the shaker hole in the hood overlooking the carb

Secondaries not budging

Everything's correct on the rebuild (I've done it countless times in the past), so I'm baffled as to why they'r enot opening

 

It still does not make it a mechanical secondary!! you WILL experience a lot of bog when you mash that pedal at idle why don't you buy the proform 750 double pumper main body for 100.00, look for double pumper metering block for the secondary, buy another set of nozzles, and do it right instead of adjusting, kicking yourself in the a$$, readjusting, rekicking, readjusting buy a used 750 baseplate as long as it is a doublepumper style, total cost should be around 175.00, one third of what a double pumper is new..

 

The secondary system of a Holley four barrel carburetor can be either vacuum
or mechanically operated.


The opening rate of a mechanical secondary system is pre-determined by the
linkage which is usually designed to allow the secondary throttle plates to
begin opening once the primary throttle plates have rotated open about
40 degrees. Special Holley kits are also available which will allow the
conversion to 1:1 linkage (primary and secondary throttle plates opening
simultaneously) for special racing applications.


The opening rate of a vacuum secondary system is controlled by the diaphragm
spring located in the vacuum secondary diaphragm housing. A "lighter" spring
will allow the the secondary throttle plates to open more quickly. A spring
assortment kit, Holley P/N 20-13, is available to help you "tailor" the secondary
opening rate to your application. A "quick change" kit, Holley P/N 20-59, is also
available for fast and easy access to the spring. It consists of a two-piece
secondary diaphragm housing cover which, after it's installed, can easily cut
in half the time required to change the secondary spring.


DO NOT put a screw in the linkage of a vacuum secondary carburetor to
mechanically "force" open the secondary throttle plates. Normally there is an
accelerator pump on the secondary side of a mechanical secondary carburetor.
The purpose of the secondary pump is to inject additional fuel to "cover" the
transition time up to the point when the secondary main system starts to
flow. Without this secondary pump shot the engine will go to an instant
lean condition. Therefore, forcing the secondaries to open prematurely will
hinder performance and may cause an engine backfire.

 

If it ain't opening then you're not building vacuum in the vacuum servo on the pass. side of the carb that opens the secondary throttles. This is often becuase the diaphragm, which also serves as the gasket that seals it up, isn't sealing up. You're leaking vacuum past it and there isn't engough vacuum left inside it to overcome the spring tension.

OR..... you have it installed "clocked" the wrong way. There a single hole it it (other than the 4 screw holes) that has to line up with the vacuum port. If it's clocked wrong it'll block the vacuum passage and you'll never get any secondary opening.

Don't forget the little check-ball that sits in the bottom part of this diapragm housing. It's job is to slightly block the passage so that vacuum is applied SLOWLY so the secondaries also open SLOWLY, avoiding a bog. However, when you let off the throttle the check ball unseats and the diaphragm can extend again quickly (closing the throttles quickly).

These secondary diaphragm assemblies are WICKED TOUCHY. I have often spent the better part of a half hour assembling and reassembling until I got it assembled perfectly.

The only other thing it can be (besides the gasket on the side of the carb which you've already checked) is that the vacuum passage that feeds this diaphragm is plugged. This is super super rare. It's not something that gets blocked up- but check anyway. Spray some carb cleaner through the diaphragm vacuum port on the side of the carb and see where it comes out. It should come out of a little tube in the pass. side primary venturi- that's where it draws vacuum from. There is also a smaller side-passage that comes out in the passenger side secondary venturi that is also connected to the diaphragm port.

It's a very simple system, actually. Very little that can go wrong with it, other than assembling the vacuum diaphragm assy. correctly and making sure the vacuum passage is clear.

 

I like to squeeze the assembly together like a sandwich in my left hand. Makes it easy. Also use WD-40 on the screws so they don't grab the diaphram and tear it.

Plugged passage happened to me once. A bit of material from flaking diaphram housing to carb body gasket, as described in link I posted earlier.