[Viet Nam Vette]

I'm running a GMPP ZZ502 Deluxe which comes with a Holley 850 CFM Vacuum Secondary Carb Model # 0-80531. This carb is flowed for the 502 motor and the Holley part Number is only for this carb for the 502. The motor is in my 65 Corvette Cp with a Keisler 5sp OD Tranny and 3:36 rear.

I installed a filp top lid on the Vacuum Secondary chamber which lets you change the spring that controls pull in time for the secondaries. I started with the lightest spring. But I was not able to get it to bog like they say should happen with the lightest spring and then work up.

There was an improvement in the responce time and feel ..but not like you would think. It still just doesn't have that "Rip out feeling". It does start to pull faster then before but there is still that waiting for the secondaries to open feeling.

Now I have read all the do's and don'ts that come with the spring kit... you know like ...don't remove the ball check valve ..or don't cut the spring....Blah Blah Blah. And I also read al the poop about the air cleaner.

Now a friend of mine who nows his way aroud holleys says to remove the Ball Check Valve in the Vacuum Chamber.. and move up one spring to see what happens.. Of course the techs at Holley on the phone tell you this is a No No.

Have any of you run into this situation?? And or what have you done to improve the secondary responce..Now I'm not looking for a Bog ..or a Lag feeling...just a get T F up and go feeling ..

Thanks..Mark

[johnsongrass1]

Why not convert to 1:1 secondary's?


You should never feel the secondary come in. Verify the secondarys even open with a paper clip on the linkage.

[302 Z28]

The seat in pants feel of the secondaries coming in is actually detrimental to performance. As stated above, you should not feel the secondaries come in.

Vince

[1ownerT]

I think the point was that he wants to feel the bog, then stiffen the spring until it is gone.

[Viet Nam Vette]

Originally Posted by 1ownerT

I think the point was that he wants to feel the bog, then stiffen the spring until it is gone.

We have a winner.. That's excactly what I'm talken about...Don't want to feel the bog or the lag ..that's a no good... as stated above.

Just want some more balls....

[Viet Nam Vette]

Originally Posted by 302/Z28

The seat in pants feel of the secondaries coming in is actually detrimental to performance. As stated above, you should not feel the secondaries come in.

Vince

Heh Thanks Vince... Yep I know all about the secondary operation. Like you say if you feel that learch or slight bog ..there set wrong.
I'm just at a point where I have done all the factory adjustmets and I'm not happy with the results.

I used the lightest spring and it still doesn't bite like I think it should ..

[Viet Nam Vette]

Originally Posted by johnsongrass1

Why not convert to 1:1 secondary's?


You should never feel the secondary come in. Verify the secondarys even open with a paper clip on the linkage.

Heh Thanks for the reply......

Yep..I know you'r not supposed to feel them suckers come in.

Ok Edge-A-Ma-Kate Me here....

(1) How and where do I put the Paper clip to check the opening of the Secondaries....

(2) How do you convert to 1:1..are you saying ..both sets of Throttel plates working at the same time??

[jtybt]

I work on boats so this may not apply.

What power valve do you have(in/hg)? The higher the #, the earlier it will open. Normal street operation for economy would probably have a 5.5. Try a 6.5 to 7.5 or higher PV and lighter spring. Matching power valve to secondary opening should give you a kick in the pants.

[Viet Nam Vette]

Originally Posted by jtybt

I work on boats so this may not apply.

What power valve do you have(in/hg)? The higher the #, the earlier it will open. Normal street operation for economy would probably have a 5.5. Try a 6.5 to 7.5 or higher PV and lighter spring. Matching power valve to secondary opening should give you a kick in the pants.

Here's the read out from the PDF on the Carb

Prim Jet 78...../Sec Jet 82/ /Pump Discharge Nozzle .040/ Primary Power Valve ..45/ Secondary Power Valve 35 / Stock Spring ..Pink/ Now has the lightest one in the Vacuum dia White.

[jtybt]

Do you have a vacuum gauge to hook up to the intake manifold? This will help to explain what's happening while the engine is running I have a large vacuum gauge on the dash so I can monitor the engine all the time.

At idle (throttle plate closed) the engine is sucking air but the throttle plates aren't allowing air in so there's high vacuum in the intake manifold(assuming you don't have too radical of a cam). As you open the throttle, the primary plates let in more air and the vacuum lowers. The power valve starts to dump extra fuel when the vacuum reaches the rating of the power valve. in tour case, 3.5 and 4.5 in/hg(vacuum). The more load the engine is under the lower the vacuum reading will be for any given throttle opening. By putting in a higher vacuum power valve, the sooner the PV will open which corresponds to lower throttle opening or lower load that the engine feels. You want to adjust/change the vacuum spring to correspond to the PV opening.

But remember, I work on boats and a boat is under ever increasing load as the throttle is opened. It's like towing a trailer uphill in 4th gear. Also a boat engine has to be run richer because of the load(to reduce the chance of detonation)

[Viet Nam Vette]

Originally Posted by jtybt

Do you have a vacuum gauge to hook up to the intake manifold? This will help to explain what's happening while the engine is running I have a large vacuum gauge on the dash so I can monitor the engine all the time.

At idle (throttle plate closed) the engine is sucking air but the throttle plates aren't allowing air in so there's high vacuum in the intake manifold(assuming you don't have too radical of a cam). As you open the throttle, the primary plates let in more air and the vacuum lowers. The power valve starts to dump extra fuel when the vacuum reaches the rating of the power valve. in tour case, 3.5 and 4.5 in/hg(vacuum). The more load the engine is under the lower the vacuum reading will be for any given throttle opening. By putting in a higher vacuum power valve, the sooner the PV will open which corresponds to lower throttle opening or lower load that the engine feels. You want to adjust/change the vacuum spring to correspond to the PV opening.

But remember, I work on boats and a boat is under ever increasing load as the throttle is opened. It's like towing a trailer uphill in 4th gear. Also a boat engine has to be run richer because of the load(to reduce the chance of detonation)

I have a Gauge but not dash mounted. The motor pulls about 15Hg's at idol.

I'll have to get further into this . Thanks

[hotrodf1]

Did you say you had a white spring in there? I could be mistaken but I thought the two lightest springs in the HOlley spring kit were Yellow (Short) and yellow (long).

Also I looked on the package and they show values for opening and fully open based on the displacment of engine. On a 400 CI engine, with the lightest spring, you still don't open all the way until over 5000 RPM.

So a vac. sec. will never be like a mech. sec. carb in my opinion. But I run a vac. sec. in my camaro and my 48 PU and I think they work quite well so i stick with em.

[Viet Nam Vette]

Originally Posted by hotrodf1

Did you say you had a white spring in there? I could be mistaken but I thought the two lightest springs in the HOlley spring kit were Yellow (Short) and yellow (long).

Also I looked on the package and they show values for opening and fully open based on the displacment of engine. On a 400 CI engine, with the lightest spring, you still don't open all the way until over 5000 RPM.

So a vac. sec. will never be like a mech. sec. carb in my opinion. But I run a vac. sec. in my camaro and my 48 PU and I think they work quite well so i stick with em.

I would assume that with a 502 it would be fully open at a much lower RPM
with a lighter spring

What's weird here is that the 20-13 Kit comes with a White spring. But The instruction sheet that's in the box says nothing about it ..Not listed.

Now go out to Holly.com Here's the link..

http://www.holley.com/data/Products/...199R8219-2.pdf

And look on page 2 of the PDF.. and you'll see the white spring listed as the lightest.

If the link does not work go to holley.com and punch in 20-13 and it will come up .then look for the instruction sheet.

There isn't a spec shown for the opening RPM or the Full Open RPM. FREAKEN Neat huh..... That's why I'm not a big Fan of Holley Carbs. But I'm stuck with this sucker as it is flowed for this motor. And I'm to lazzy to start pulling stuff off and on.

I guess I just want An "Easy" Button to Push.

[coldknock]

Try the short yellow spring. I have a 750 with that spring on a 400 small block and it's wide open at 5200 rpm. No bog at all.


Larry

[Viet Nam Vette]

Originally Posted by coldknock

Try the short yellow spring. I have a 750 with that spring on a 400 small block and it's wide open at 5200 rpm. No bog at all.


Larry

Heh Larry..

Yeah But....... ... The White is the lightest..and I want them suckers open way before 5200. The max RPM on the 502 is 5500 RPM's. The MSD Rev Limiter is set for 5200.There's gotta be a way to get the secondaries open sooner then they are.

I mean...you read the instructions...you buy the top cover kit... then you buy the spring kit. It says ..use the spring that causes a bog then work up from their.

Ok I did all that..and the POS carb still won't do what it's suposed too. Then people tell you ..take out the check ball in the housing ..some tell you ...cut the spring....Holley Tech Guy says's noooooooooooooooooo..!!!! don't you dare do that it's wrong.!!!!!

It'll Blah ..Blah ...Blah... So what's all this tell you..... It tells me GMPP should have gone to Edelbrock and had them flow one of there new AVS..(Adjustable Vacuum Secondaries) Carbs for the 502..instead of this leaky POS that's on my 502 now.

If I wasn't so lazzy.. I'd but an Edelbrock and Flow one for my ride. But that would take alot of time and Jet changes to do. At least if I wanted to adjust the secondaries all I would need is a screwdriver.. .. Not a bunch of freaken springs and covers and....still the POS won't work...

I feel better now that I Ranted this off my chest.

Thanks for listening..

Maybe I'll email Holley and dump on them.....