I have a 1986 Trans am and i purchased a new crate engine and transmission for the car and im running into some tech problems with the carb setup. WOT i dont get any action from the 4 barrel. For whatever reason the 4 barrel does not open up. If i hit the gas real hard to the floor it hesitates before taking off as well. I hooked up vacume gauge and adjusted the air fuel mixture on both sides of the carb and it seemed to help. I also double checked the timing but it checked out.
Now you probably asking how i know the 4ballel isnt openeing up and thats because i put a paper clip on the vacume secendary and took the car around the block and popped the hood and the paper click never moved on the linkage. Please someone out there has to have some advise. This is my second brand new carb taht has done it too.

 

Your post title says double pumper but your text says vacuum secondary. What's the list number on the carb?

Vacuum secondarys on Holleys are easy to screw up. They work on venturi vacuum primarily from the primary side of the carb to open the secondary barrels. If there is a vacuum leak (between the cansiter and the vacuum port on the side of the carb or at the canister diaphragm/gasket itself) it will never open the secondaries. Linkage problems between the canister and the secondary throttle arm are possible, but less likely- it's only one metal rod and a clip. Has the carb been "rebuilt?" If so, it probably got messed up during that process.

Now, if this has happened on several different carbs then I would question your method of testing. Perhaps the paperclip is actually preventing it from opening. It works on only very light amounts of force. Also, unless you have a light spring in the vacuum chamber it's not uncommon that the secondaries never get fully open. Also, you shouldn't ever 'feel' the secondaries open when driving it. Should be basically undetectable.

I often disconnect the secondary linkage between the vacuum canister and the secondary throttle arm as a temporary diagnostic tool (take the secondaries completely out of the tuning picture). Take a spin, see how it reacts to quick throttle stabs and such. If it was a problem with the secondaries the problems will magically disappear. If it's not, they won't.

 

Its a brand new carb. so was the last one. I bought the motor as a " turn key" package and now ihave some tuneing issues. I have been told the light spring is a option but i havnt ordered it from holly yet. Do you have and idea as far as the hesitation i get with a quick stomp of the throttle. Like it is choking out. it wants to fall on its face when i hit it quick

 

Post a picture of the carb. Please. Also what your describing could be related to the dist and timing.

 

here are some pics, hopefully it helps

 

Looks like a model 3310. Do you have the list number? Should be stamped on the choke tower.

What do you have the base ignition timing set at? How much total advance are you running? 8-12 degrees of intial advance should get you in the ballpark.

If the timing checks out, I would experiment with different accelerator pump nozzles and cams. Can you see what size squirter nozzle and color pump cam you have installed?

 

The throttle return spring is on the wrong spot.
Should go under below the linkage pivot point and anchored to the rear.
(A lot easier on the carb throttle blade shaft with less spring tension.)
less driver foot fatiague. Not as likley to pop the return spring off when the throttle snaps shut from WOT.)
Which crate motor are you working with?
What is the trans converter stall speed and rear gear ratio?
Have you make any attempts at dialing the accelerator pump shooter or plastic cam on the linkage? Do you get fuel shot out of the accel discharge nozzles immediately upon slight movement of the throttle linkage or is it delayed?
What is the initial timing at idle, idle speed in gear and total maxed out mechanical timing?

The choke flap should be all the way open when the motor is warm.

 

what is the list number on the air horn?

 

Thanks for the pic, i went out and all i did was change the return spring from the front to the back and eliminate that second bigger spring and it alowed the 4brll to open up. not much but it did move, maybe a 1/16 of an inch slide for the paper clip. That tells me that now i should change the spring to a lighter spring to allow the 4brll or open up even more. thanks for that picture, it really helped.

 

the timeing is set right now at 13 advanced , the engine calls for 10 but it seems to run better at 13

 

The throttle return spring has nothing to do with wether or how fast the secondaries will open.

You will not see the secondarys open by winging the throttle open in neutral.
To see if your secondaries are opening, temp disconnect the sec vac pot linkage (passenger side) and block/wire the sec throttles closed so they cannot open. Go for a ride and test the acceleration on just the primary barrels.
Now stop and reconnect the sec vacuum pot linkage and go for another ride.
You should feel a smooth progressive power increase as the rpms come up and the secondaries open automatically. If there is no difference at all in acceleration, remove the sec vacuum pot housing from the carb and test the integrity of the vac diaphram seal by compressing the linkage rod and then block the vacuum feed hole on the housing, with your thumb.. The rod should remain compressed until you release the vacuum hole. There is a small round cork gasket that seals the vacuum seal passage between the carb body and the vacuum pot. if it is missing or mis located or the diapharm is leaking, the secondaries will not open.
The vacuum diaphram and housing must seal and the housing must seal against the side of the carb body with the little round cork gasket.
There are various different tension vac diaphram springs that u can use to adjust the vac sec opening rate. usually a plain steel , purple, or yellow colored spring is just right.
Get an advance type timing light and or a balancer timing tape to allow you to read the max advance timing at high rpm.

Your motor will provide maximum performance when the timing is set to max out at 34 to 36deg BTDC at high rpm (vacuum advance disconnected).
A stock GM HEI distributor should have 20deg of mechanical advance built in.
So when you time the motor for max 36deg BTDC at full advance, the idle timing should be 16deg BTDC at idle (700-750 rpm in gear). This is the timing advance range you are looking for. 16 static initial + 20deg of mechanical advance =36deg BTDC. if you cannot achieve this then the mechanical advance mechenism needs to be modified and set up correctly.
The mechanical advance is controlled by centrifical weight and springs and limited by an advance stop pin with various bushings in a slot under the advance weight plate.

Vacuum advance should add an additional 12 to 15deg of timing while cruisng on the hiway at part throttle. You can buy a an adjustable replacement vacuum advacne from crane cams for your HEI distributor.
You can set up the vac advance rate and limit as required.

Make sure the max mechanical advance does not exceed 36deg BTDC and the combined mechanical+ vacuum advance does not exceed 51deg combined.
Get a timing light and check.
Proper ignition timing advance and carb adjustment will give you the performance you're looking for.
Your motor needs 92 octane fuel. 87 octane junk won't cut it.

If you don't under stand this, get someone to help you, that does.
You can read all about setting up and adjusting and tuning your holley carb in the tech pages at www.holley.com.

 

One other thing I notice from the picture, aside from the good advice you're getting, above, is that you are using the wrong throttle cable stud. That real long sucker you have your throttle cable hooked up to is for cruise control. It will bind the throttle linkage as you approach WOT becuase it's way too far offset from the throttle cable mounting point. You need a stud that only sticks out about 1/2" from the throttle arm.

This one happens to be from Edlebrock, but Holley sells something similar (and either will work), I just don't have the holley one at my fingertips right now:

http://store.summitracing.com/partde...0&autoview=sku

Also, it doesn't go in the hole you're currently using on the throttle arm. It goes in the small hole just above the one you're using now. You will certainly need to readjust your throttle cable mounting point once you're using the right stud in the right position- your cable mounting point will probably need to be moved back from where it is now to allow full throttle opening.

 

I disagree. A free body diagram will show why putting the return spring to the front is the proper way to put the least stress on the throttle shaft.

 

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Basics physics. For a body at rest, all forces acting on it have to sum to zero (cancel each other out). Movement occurs when force is unbalanced. Often described as "equal and opposite" forces. A "free body diagram" simply illustrates the forces acting on a body.

In this case, pulling back on the throttle cable is resisted by the spring and throttle shaft. If the spring is on the bottom and anchored to the rear, both the force of the throttle cable and spring have to be resisted by the throttle shaft, meaning the throttle body is exerting a force on the throttle arm equal to the sum of the force of the throttle cable and the return spring.

If you put the return spring on the top and anchored to the front, the throttle cable and spring are pulling against each other, and the throttle shaft force is minimized.

If you want to reduce wear on your throttle shaft/throttle body, put the spring on the top anchored to the front. The factory "shafted" us on this one.

 

I had issues with the stock throttle cable not allowing me to go to WOT. Simple but you may check that. When I pushed the peddle to the floor the carb wasn't going WOT.

 

actually that was a part of the problem. I bought this motor as a " turn key " package and the bracket they gave me was a universal backet and wasnt for a holly and a 700r4 combo and it wasnt allowing the it to get to WOT and also wasnt allowing the detent cable to work properly. I have recently purchased the right ones and im waiting for them to be shipped here. Hopefully that takes care of the majority of the problem. the second problem is the springs in the secondaries.

 

I'm doing something similar with my swap, I'm supposed to get it very soon. It's basically the same motor, same year. I did have to order different linkages and kick down plates, in addition to the posts/studs to hook up the linkages to.

Once I get it I'll snap some pics for comparison. The guy that's doing it made his own linkage assembly to get things to fit and move freely, so not sure if he used the one I picked up.

 

Here's the pics of the carb set up, copied from my thread:

Carb-Side

Carb-Front

Carb-Back

Sorry the last one is a bit fuzzy, my camera is a piece of crap. Took 4 shots just to get that one.... hope it helps!

 

Thanks, it looks like we bought the same carb brackets and all. thats about the identical setup i have now. Have any trouble with setting your detent cable?

 

Mechanic said not really to the Detent issue, the cruise control was the pain in the butt. Still doesn't work right but that's ok, if it worked it worked, if not no big deal.

Glad the pics were of some use

 

Guys...could you also give out the carb set-up/ prim. jet size, how do you get the engine to idle without being rich? I have that same set-up, but the dang thing still runs rich even with the mixture screws turned 0.5 turn out. Car runs like a bat outta hell, though stinkin' rich.

 

Going to look into that at some point, i have the same thing on mine. Hopefully we can get it running so it's not so stinky at idle hehe!

 

Much appreciated!

 

Hey is that an zz4 engine? I have an edelbrock carb. (one from autozone) on my zz4, and it would help if I know the car batttery (charges, etc.), alternator amp, and what size if matters for carb? I have an 85 camaro that I'm trying to restore with the engine having rings promblem as well, so I'm having to rebuild it. Not sure if 2500 was worth it now :L