Thread: New ZZ454 and parts, engine bog?

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Hi. I'm sorry to trouble the experts here, but I'm a bit stumped. I have a brand new ZZ454 that I'm putting in my 69 Camaro and I'm having a bit of trouble with it. I just fired it up for the first time about 2 weeks ago(how sweet that was!). From day one, when I hit the throttle quickly, I get a pretty severe hesitation/bog and I'm having a bit of trouble determining the problem. Also, for some reason, it just doesn't seem like it's running smoothly. I notice a bit of vibration in the upper RPMs, but that might be something totally separate from the engine bog. All parts are absolutely brand new:

New GM ZZ454
Holley 750CFM, 4160, electric choke, vacuum sec, HLY-0-80508S
GM HEI distributor
Holley mechanical 110GPH mechanical fuel pump
MSD-8500 Super HEI Kit, with 6AL ignition and Blaster 2 coil
Taylor Thundervolt 8.2 wires, stock plugs that came with engine.

Here's what I've checked:

1. I have a fuel pressure guage located after the filter(which is clean) and it reads a steady 6.8 to 7.0. With 9.6:1 compression, the premium gas should be fine.
2. The carb is untouched out of the box. It's the 2nd new carb I've used with the same results. Fuel levels in the bowls look good.
3. Timing is set to GM's recommendations, 12 degrees BTDC at idle, about 36 BTDC degrees at 3000rpm. I timed it with the vacuum advance disconnected and plugged. The vacuum advance is now hooked up to the vacuum correct port on the carb(idle smooths out a bit and goes up a few 100 rpm when I connect the vacuum advance).
4. No vacuuum leaks(I've checked and double-checked), with vacuum good at about 12 - 15 at idle with my vacuum guage hooked up to the manifold port.
5. My PCV setup looks like it's hooked up properly.
6. I've used a second set of new spark plugs and wires just to be safe with no change in behavior. Gaps on the plugs are good(.045) and the plugs look pretty clean.
7. I've actually gone back to the stock HEI setup and coil just to be sure it wasn't the MSD setup and that made no difference either.
8. All my ground wires/straps look good and are touching good metal.
9. I've tried going around the distributor, removing one wire at a time but the engine dropped RPM consistently when each wire was removed(and it'll shock the heck out of you if you don't wear rubber gloves!).

The engine starts right up fairly easily and seems to idle okay(a bit rough though until it warms up in about 2 minutes). I notice a bit of vibration at higher RPM's(2000+), so I'm not sure if that's related(?). I can't imagine there'd be anything wrong with the long block itself. I was going to disconnect the new torque converter from the flex plate and the drive belts to check on the slight vibration, but I'd like to solve the engine bog/hesitation first. So I'm stumped on this one. I wouldn't think I would need to change the stock carb settings to eliminate the bog, nor should I have to move away from the stock timing settings. I was under the assumption this stuff would perform pretty well together right out of the box.

Any ideas? Your feedback is really really appreciated!!!

-Chris

My ZZ430 was doing the same thing, and I found that the electric choke wasn't working worth a darn. Since the weather's warm here, I cranked it pretty much wide open, and the bog/hesitation went away.

Also, have you checked your fuel pump shot? You should get a squirt even with a tiny bit of linkage travel.

this is from holleys question section, i also think the fuel pressure is a tad high @ 7 lbs, 6 lbs is a more realistic number for the set up.
i can remove my fuel line and @ 6 lbs fill a 5 gallon jug in about a minute with about the same pump you have.

QUESTION I have a vacuum secondary carburetor that bogs when the secondaries come in. What will cause this?
ANSWER Bogging and hesitation are caused by the secondaries coming in too quickly. You can install a heavier secondary spring and this will prevent the secondary from coming in too soon. If the engine is sluggish in response at full throttle then the secondaries may not be opening soon enough. You will then need to go to a lighter spring. The spring kit is part number 20-13 which will have 7 different springs to fine tune with.

Thanks a bunch for the quick replies! I'll try playing with the choke when I get home from work today. If that doesn't work, I'll see about getting ahold of a fuel pressure regulator. I'm using a Summit fuel pressure gauge and I've heard they aren't necessarily the most accurate, but being able to adjust the fuel pressure was something I thought about setting up anyway. Again, I appreciate the advice!

I use white cam that go where the fuel pump squrter arm Located. It will take the bog out for sure. And be sure put the screw that hold the cam on in Number Two hole.