4 barrell carb question need help here Pics Added

[darrin75]

I have a 750 holly carb with a 509 cam.

First how much should I adjust for the four bareel to kick in.  Does it need to be all the way open.  Also, is there a secret to adjusting it.  It seems at wide open my back barrells barely open, and my cable has been adjusted all the way.  Any suggestions, also It seems to want to stall whne under a load, roughs fine at idle.

[Ghoste]

Vacuum secondaries?

[bandit67]

From your post I assume you have not had  a lot of experience with Holley carbs. May I suggest getting one of the many books that will explain the five major systems that make up a carb and how they work. That basic knowledge is most valuable BEFORE one can begin to fine tune a carb to the needs of a specific engine. I have one from HP books and still refer to it often.  When you begin adjusting things on a Holley , not knowing exctactly what it does,  it is very easy to make things worse. I think that is why there are sooooo many used Holleys  for sale at swap meets and ebay.

[firefighter3931]

Is the carb a vacuum secondary or double pumper ? What size engine ?

The 509 is a difficult carb to tune on the street without the right carb....you will want a double pumper which has a more agressive "fuel curve" to make this job easier.


There are lots of tricks to tuning a holley ; power valves, squirters, accelerator pump cams etc....



Ron

[darrin75]

double pumper 383 engine

[firefighter3931]

Check the linkage on the (passenger) side of the carb to make sure it's not binding.


Ron

[darrin75]

later on this evening I plan on posting pics, maybe that will help.  thanks for the replies.

[darrin75]

Here the pics to help.  I have drawn a square around the thing I need to adjust.  Hop someone can help.  No matter how much I either adjust the cable etc.  This never gets opened, One side note What degree Do I need to set my timing I have 383 four barrell 750 holley double pumper electronic ign, and 509 cam. 15*?

[chargerbr549]

The part you have in orange is mainly meant to manually close your secondarys when you let off the throttle otherwise they could probably stay open, the vacuum diaphram on the passenger side of the carb is the one that opens the secondarys when you get enough vacuum signal through the venturies on the primary side of the carb, the way you adjust the opening is to use different types of springs too taylor when the secondaries come in, also you need holley part number 20-7 for the correct way to hook up your throttle cable, it keeps your throttle ratio just like the stock set-up.

Kevin

[darrin75]

thanks for the reply, but I thought double pumper's were manuall four barrells, no vaccum.  But I could be totally wrong here.  I am no mechanic.

[firefighter3931]

Kevin is on the money....you have a vacuum secondary carb and the secondary opening is controlled by springs in the vacuum pod. You won't be able to open the secondaries unless the engine is under load....revving it in park or neutral won't work. Just try to manually open the secondaries to make sure that they're not bound up.

As for timing, it's gonna want at least 15* at idle but i would guess 20* would be better....that's a huge cam for a 383.




Ron

[darrin75]

So do I get springs from holley.  So I open up the thing that has the diapram in it, to replace the spring.  Because I can have it on the floor and I know I only have two barrells working only.

[darrin75]

Well, something came to mind,  My kickdown is not coming in right, I bet that has to do with my secondaries not working correctly,  I assume because I have no high rpm to open them correct?

[firefighter3931]

Well, something came to mind,  My kickdown is not coming in right, I bet that has to do with my secondaries not working correctly,  I assume because I have no high rpm to open them correct?

It's possible that the KD linkage is impeding the throttle from opening completely. You should be able to have the throttle fully open and still have a small amount of play in the KD linkage. 

On your setup i see that you have a cable kickdown....try disconnecting the cable and have someone put the pedal to the floor to see if the throttle is opening fully.


Ron

[Chatt69chgr]

Holly sells a vacuum secondary spring kit so you can change springs and get the right actuation point.  In fact, they sell a quick change top for the vacuum secondary diaphram assembly to facilitate changing the spring.  You will find these items described on the Holly website and they can be ordered from Summit. 

[tecmopar]

That rod going into the secondary blade slot doesn't look right at all. Also, Ron is right about that being a lot of cam and carb for a 383, good luck.

[darrin75]

ok got the spring kit, my secondaries the best I can tell are not opening at all, i have one of the yellow spring on it, got the car up to about 90 mph, witha string tied around the vac rod and no movement at all.  What could be the problem here??