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Discussion Starter #1
:confused::confused:Ok...swapped a new Holley 670 Street Avenger carb w/ elec choke onto my ZZ4 350 and had a stumble when I stabbed the throttle.... I tee'd the vacuum lines together and installed the heavier spring for the vacuum operated secondaries....the stumble is now gone. The problem I have now is that the motor only seems to rev out to about 4500 rpm give or take when before I think it reved out to more like 5500 ( Im not 100 percent sure of the 5500 rpm figure, but it feels like the car isnt reving out to redline so to speak..to me, the only way to know for sure is to put back on the edlebrock unit that was on there...).

Im a newbie when it comes to carb tuning so here is what IM thinking of doing

the primary metering jet on the 670 is a 65 and the secondary a 68

Im thinking of putting the 68 as the primary and ordering a 72 for the secondary, Im thinking Im running out of fuel and the car wont tach out....possible? I figured for the 5 bucks for the 72 it might be a cheap trial and error.....

the timing is roughly 10 degrees advanced in case anyone was wondering

on the flip side...maybe, but it couldnt be this simple im sure...is I need someone to ride behind me when I hammer it...see what color smoke Im making if any, maybe that'll show if its getting a little too much gas(black smoke?..had none before w/ other carb)...which might cause the same prob possibly? might be flooding itself out/chocking itself off? seems I smelled a little raw gas but after the swap it could have been just residual on my hands/clothes?

The only other thing you might wanna know is Im running a good Holley Mechanical fuel pump...seems to be putting out the right pressure all through the rev range with no drop in pressure according to the guage so I've ruled that out...

any help or ideas would be greatly appreciated...the car runs great ...just seems a little flat on top since the new carb install.....thanks guys...Nick
 

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Discussion Starter #3
Im just going by my Autometer Tach inside the car, the seat of the pants feel inside the car seems a little lacking as well as the engine sound as compared to before....its alsmost the feeling of having your floormat stuck under you pedal....seems like you should just have more rpm...I checked to see if I was getting a full stroke on the carb linkage too and I was good there and nothning is interfering with the pedal so here we are.....
 

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Discussion Starter #4
the specs for my ZZ4 say 355 horsepower @ 5300 RPM according to GM listings...so Im assuming the redline might be around 5500.... Im lucky Im getting over the 4500 mark with the street avenger carb, I def was well over 5000 before with the other Edelbrock carb. It just doesnt scream on the top end like it used to.....Im sure we'll fig it out! like I said Im no carb specialist so Im sure a little trial and error is in store...lol thanks...Nick
 

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What intake do you have on the engine?
I ask about the intake because if your using a Edelbrock Performer did you install the carb adapter plate for the Holley?

Do you have the vacuum port on the back of the carb sealed? Or run to something that is sealed?

The secondary spring change was too heavy you have cancelled the secondary.
Are you sure during the reinstall of the spring the chamber is sealed?

Jet change is not needed. IMO
 

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Discussion Starter #6



I believe it is the dual plane aluminum intake that is an option when you buy the crate ZZ4...not sure of any specs.....


an interesting thing I found though is..... an option when you buy the engine is....a holley 770 carb...so maybe Im going in the right direction with the bigger "roughly 770 size" jets to give me a little more fuel.....
 

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Changing the jets won't give you the equivalent results--I would have used a 750 or 770 carb to start with, but too late now. Like Al said, you probably went too heavy on the spring and the secondaries might not be opening all the way.
Put the stock spring back in the carb, bump the timing to about 15 degrees, and see what happens.
 

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Discussion Starter #9
not sure on the intake...it has the chevy emblem right in the casting so Im assuming it is the GM unit that comes with the ZZ4 crate engine, dont think edelbrock is going to build something without putting there name on it anywhere, but I could be wrong, many out there know more than I ...that's why Im asking... I can hit a little starting fluid around the base of the carb while its running...see if it takes off, should mean I have a leak right? eveyhting seemed to bolt up fine with the new gasket....again...thats something Ill have to check out...gimmie a few days to switch the springs out and adjust the timing and we'll see what happens...I'm actually out of town for the weekend....I'l see what I can do when I get back...I appreciate the info guys....:beer1:
 

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not sure on the intake...it has the chevy emblem right in the casting so Im assuming it is the GM unit that comes with the ZZ4 crate engine, dont think edelbrock is going to build something without putting there name on it anywhere, but I could be wrong, many out there know more than I ...that's why Im asking... I can hit a little starting fluid around the base of the carb while its running...see if it takes off, should mean I have a leak right? eveyhting seemed to bolt up fine with the new gasket....again...thats something Ill have to check out...gimmie a few days to switch the springs out and adjust the timing and we'll see what happens...I'm actually out of town for the weekend....I'l see what I can do when I get back...I appreciate the info guys....:beer1:
if it is the GM intake it will not need it.

just for the record some have PM'd me and ask.

If the carb flange looks like this and it is a "EDELBROCK" you need the plate for your intake for a sqaure flange carb.
 

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Here is the ZZ4350 intake if it helps.



-Justin
 

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Al, why do you suggest a special plate? I have run two of those performer intakes both with Holley 1850's and never needed anything special? One has been together for 8 years and no vacume leak.
 

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Al, why do you suggest a special plate? I have run two of those performer intakes both with Holley 1850's and never needed anything special? One has been together for 8 years and no vacume leak.
I SAID IF HE HAD A "EDELBROCK" HE NEEDED IT!

All you have to do is ask "EDELBROCK" WHY?


He is looking for a problem. I have seen 2 cases of use of the Edelbrock intake that had leaks without the plate.

Copy from Edelbrock,
Square-bore to Spread-bore Adapter Plate (1.16" thick, for Edelbrock manifolds only)
Mounts square-bore carbs to spread-bore carb pad on Edelbrock intakes (except #2101 & #3701). 2732


http://www.edelbrock.com/automotive_new/mc/install_items/adapters_spacers.shtml
 

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that is my exact intake ...thanks JMDC
I was making a suggestion for a problem that might exist.

You said you had a optional intake, that is the standard intake for a ZZ4.

I still say the Vac secondary spring is your problem.

Good luck Al
 

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Discussion Starter #17
Im gonna check that spring when I get back in town Big AL...thanks for the help, It's greatly appreciated....Nick
 

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I saw in one of the first posts that the timing was 10 degrees advanced. I assume that is initial timing but even that would make my motor awfully weak. I'd verify that you are getting around 34 - 36 degrees total advance by about 3000 rpm with the vacuum advance disconnected and the line plugged. If that's Ok then you can go back to the carb and look some more.
 
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