Need some help with tuning issues with my ZZ4 motor. I bought a Camaro with the ZZ4 motor installed and running, but not running as it should, it is a stick shift car. The issues I had were: idle was set to high, timing was incorrect, engine run on after shut off and the motor would pop through the carb when starting up from a stop if you let the rpm go to low. The timing issue was due to the HEI being installed 1 gear off so the vacuum unit hit the intake manifold and the correct timing could not be set. That has been changed and the timing is set at 32 degrees total and 6-7 at idle. I see some suggest total timing at 36 but most say to go with 32 degrees so I used that. Also had carb issues with a 750 edelbrock so I changed to a new out of the box 750 Holley and drivability is much better but the motor still will pop at low RPMs. When I get everything else sorted out I will probably go with a 650 Holley, although GM suggests a 780 it just seems like to much carb. I put small 600 Holley on it for a test and throttle response was great. I have to say that full throttle performance with the 750 is pretty impressive for a 350, but around town drivability is not where it should be. I have tried to follow suggested ZZ4 specs on timing but with the idle set at about 800rpm it will still not shut off when up to running temp. Motor has an HEI, the vacuum is plugged and I have not checked that at all but it appears to be new. I have played with fuel mixture settings from stock 1.5 turns out to 2-3 turns out as I always thought that when a motor pops through the carb coming off idle it is usually due to being to lean but this does not seem to make much difference.
Any suggestions to help would be appreciated as I am out of ideas and am to proud to take it and have it pro-tuned. It is just to simple and has to be something simple that I am overlooking.

 

By "plugged" do you mean capped off? If you do have the distributor advance can hooked to vacuum as it wants to be, which port is it connected to?
And this may sound like a strange question, but are you running an electric radiator fan? More on that one later, maybe.

 

Agree, full time vacuum on vac advance.
Use the vacuum gauge and tune/adjust for max reading.
This adjustment would include mixture screws and initial timing.

Is the engine dieseling at shutdown, too much throttle plate open,
or not shutting off electrically as in feedback voltage from internally reg'd alt installed?
If so on alt, need to route term 1 power through an ign controlled relay.

Once engine/carb is adjusted, the engine should go from idle to WOT/5000 rpm in about a microsecond, maybe two...

 

Yes I mean capped off, they actually cut the nipple off of the vacuum can and closed it off so that is perminent unless I want to change the can. I am not running electric fans it has the stock fan clutch and fan set up. It has been changed to a new alternator that is internally regulated and the wiring has been cobbled up so that is also on my list of things to sort out. I am not saying the wiring is wrong because it charges fine and starts fine but things are cut, spliced, taped and routed all wrong. I will need to back track all that to see where it has been changed. That may be where I need to go next to check it all out.

 

It's possible the distributor was converted to full mechanical. It's also possible the person who worked on it didn't know what he was doing, which is more believable from the sounds of the "quality" wiring cobble job that was done. Having no off idle-low rpm ignition advance will make the engine fall on it's face, and cough & sputter. Mechanical advance takes over the vacuum at around 2,000 rpm, but you may not have any advance up to that point. You'll want to go digging deeper into the workings of your distributor and see what was done, or undone.

 

I think it might be time to have the distributor looked at and if needed, change the vacuum can so I can run some advance at idle. Any suggestion as to how much advance is called for with a ZZ4 and would that matter if the engine has the stock ZZ4 cam or the hot cam? This motor has roller rockers and from what I have read the stock ZZR comes with stock pressed rockers, you get the roller rockers with the hot cam. From the quality of the past work I have undone, I don't have lots of confidence that things are correct.