holley 4 barrel question

[JuanJaime]

azkyinc, I too am a rather new Z owner and also acquired my Z with a Bob Sharp/Holley 390 setup. It actually runs very well and according to my butt dyno isn't too big of a slouch. The biggest complaint I have is that upon initial startup it will idle around 1000 to 1500 rpm....and then it bogs (it just dies). I start it up again and it idles for about 10 to 15 seconds and bogs once more. The whole process is repeated until I can sustain a steady idle, at which it will settle around 500 rpm. Typically, if i rev it past 4000 rpm as soon as I get it to turn over it will settle into that steady low idle much sooner. Other than that, my setup seems very reliable and I use it as my current daily driver.

[JuanJaime]

YouTube is the source of ALL knowledge.

[beermanpete]

azkyinc, I too am a rather new Z owner and also acquired my Z with a Bob Sharp/Holley 390 setup. It actually runs very well and according to my butt dyno isn't too big of a slouch. The biggest complaint I have is that upon initial startup it will idle around 1000 to 1500 rpm....and then it bogs (it just dies). I start it up again and it idles for about 10 to 15 seconds and bogs once more. The whole process is repeated until I can sustain a steady idle, at which it will settle around 500 rpm. Typically, if i rev it past 4000 rpm as soon as I get it to turn over it will settle into that steady low idle much sooner. Other than that, my setup seems very reliable and I use it as my current daily driver.

Assuming you have an automatic choke:

The fast idle when cold is normal, to a point. The choke system has a fast-idle cam that increase the idle speed when the choke is on. The stalling right after start-up sounds like the choke pull-off is opening the choke too far. Both are adjustable. Follow the Holley adjustment procedure and it should be fine.

[63ronin]

Hi all. Figured I'd post up in this thread.

I have a '78 280. Removed all the FI. Installed Arizona manifold with Holley 390 4bbl, MSA headers, 2.25" exhaust, and MSD ignition. Then the car sat for about 5 years. Brought back to life last summer. Ran like crap (go figure). Couple weeks ago I pulled the carb and tore it apart. Ran it through my ultrasonic cleaner (several times) and rebuilt using Holley rebuild kit. Stock jetting was 51 mains. I downsized to 49s during the rebuild. Had a terrible time with lag when stepping on the gas. So I changed out the accelerator pump cam the other day. Original was orange. I changed to a cam with lower total volume and more linear delivery. Lowest volume I had was a black cam. That made a huge difference on acceleration. As in it actually does now without bogging down and hesitating. Still a lot of tuning to do. But at least the thing is back on the road and comfortably derivable.

Now all I need to do is fix the stereo...

...And maybe do something obout the squealing front brakes.

Later

[Zedyone_kenobi]

well if you want to get really crazy, do not just tune the accelerator pump cam. Change out the squirter on top of the housing that discharges fuel into the carb. Those made a huge difference in the way the fuel is delivered. You can really tune a holley to do darn near anything once you get an understanding of the circuits.

[Wade Nelson]

600 cfm waaay too big even for a 2800 cc motor. It will NEVER run right.

[63ronin]

well if you want to get really crazy, do not just tune the accelerator pump cam. Change out the squirter on top of the housing that discharges fuel into the carb. Those made a huge difference in the way the fuel is delivered. You can really tune a holley to do darn near anything once you get an understanding of the circuits.

What size squirter did you go with? And have changed the diaphragm spring on the secondaries? If you did, harder or softer? And finally, what size main jets are you running?

[Zedyone_kenobi]

OH man, Okay, lets be clear. I use to run Holleys on all my Drag Cars I use to play with. I started with typical vacuum secondaries then moved on to double pumpers. Which was easy since it is the same with two sets of primaries. But I have long since forgotten about which one I used. I had about a half dozen in my carb tuning kit, about a dozen jets, and about a dozen cams. I also always had a power valve or two just sitting in there in case.

I NEVER changed the diaphragm spring on the secondaries. I do not think you need to unless you are just dying for fuel. Here is a rule I remember reading about. IF you can feel your secondaries kick in, the tune is off. They will only really open at high load settings anyway in the upper RPM band. The engine will only pull what it needs from the secondaries. So it is sort of self tuning to a degree. That is the beauty of the vacuum secondary carb. It is a great design.

You are at that point were you are trying to make very fine tuning adjustments. If the car starts and idles and runs without any noticeable flat spots then you are over half way there. I spent months thinking with my Holleys trying to eek out a tenth here and there, but I had a measurable metric. I had a 1/4 mile time. And I could tune for a specific thing, which was drag racing. Coming out the hole hard and then staying in the sweet spot to red line under Wide Open Throttle.

From what I gather you are not doing drag racing runs which can be used to quantify your results. So you can get into the circle of chasing a fantasy perfect setting where the whole car will wake up instantly. The truth is that probably will not happen. If you have a lean spot or an off idle stumble then yes, that can be tuned away to a degree. But if the car is running decently with your Holley, then without a yardstick to measure your results, you may end making things worse more than you make them better.

[63ronin]

Hell, I'm happy I just got the thing running again. I probably won't mess with it too much. I'd really like to (and plan to) go with triple webbers. But they are so damned expensive and the wife says I'm wasting enough money on my two wheeled "projects" at the moment. My biggest concern is going to be passing the DEQ test (emissions test) that is required in the Portland, OR area. Never had to try passing that before.

Drag racing a "Z"? That sounds like fun...

[Zed Head]

I saw in your previous post that you've put a new exhaust system on. They will look under the car with a mirror for a catalytic converter if the door tag says it's supposed to have one. Just a heads-up for you.

As far as the idle emissions spec. you'll get multiple tries to get it right. No fees until you pass.

[63ronin]

Catalytic converter... OMG. How am I supposed to have any fun with my "project" if they are going to make me conform to the will of "Da Man"? I'll have to check tomorrow and see what stickers are still on the car. Maybe I can pull out the middle glass pack and put in a cat. Still have flowmaster at the end. Once DEQ is done, put the glass pack back in. Registration is good till December. So I have a bit of time to sort the car out. Hell still have tuning to do on the carb for heaven sake.

Washington county Zed? I'm there as well. Hillsboro.

[ozconnection]

OH man, Okay, lets be clear. I use to run Holleys on all my Drag Cars I use to play with. I started with typical vacuum secondaries then moved on to double pumpers. Which was easy since it is the same with two sets of primaries. But I have long since forgotten about which one I used. I had about a half dozen in my carb tuning kit, about a dozen jets, and about a dozen cams. I also always had a power valve or two just sitting in there in case.

I NEVER changed the diaphragm spring on the secondaries. I do not think you need to unless you are just dying for fuel. Here is a rule I remember reading about. IF you can feel your secondaries kick in, the tune is off. They will only really open at high load settings anyway in the upper RPM band. The engine will only pull what it needs from the secondaries. So it is sort of self tuning to a degree. That is the beauty of the vacuum secondary carb. It is a great design.

You are at that point were you are trying to make very fine tuning adjustments. If the car starts and idles and runs without any noticeable flat spots then you are over half way there. I spent months thinking with my Holleys trying to eek out a tenth here and there, but I had a measurable metric. I had a 1/4 mile time. And I could tune for a specific thing, which was drag racing. Coming out the hole hard and then staying in the sweet spot to red line under Wide Open Throttle.

From what I gather you are not doing drag racing runs which can be used to quantify your results. So you can get into the circle of chasing a fantasy perfect setting where the whole car will wake up instantly. The truth is that probably will not happen. If you have a lean spot or an off idle stumble then yes, that can be tuned away to a degree. But if the car is running decently with your Holley, then without a yardstick to measure your results, you may end making things worse more than you make them better.

That's some solid info right there!

As far as the accel pump setup is concerned, it's way too big for our little sixes. The volume of fuel that can be delivered by the accel pump can easily flood our engine. The carbs were originally designed for a much larger capacity engine, so some fuel delivery reduction...in terms of volume.....needs to be done. The way I do this is to adjust the spring loaded screw and unload it, undo it so that there is much less travel on the swing arm on the bottom of the bowl/accel. pump. The effect is to use only a percentage of the volume of fuel stored in the diaphragm. This is not the way Holley will tell you to set it up. You'll find a point at which too little fuel is delivered and a bog or hesitation will be felt. To correct for this, screw back in the spring loaded bolt a few turns and compress the spring a little. Try your engine/car again. Driving is the best measure, to see if the setup is working properly. Winging the throttle in neutral isn't the answer.

I change my secondary springs. I start with the heavy black one and work, one at a time, progressively lighter, until I feel a bog or sag again. Then I swap back to the one before it that doesn't sag....all done. That's pretty easy to do. Your secondary carb tune may effect your mixtures, so I suggest you get a WBO2 sensor with data logging and do some freeway cruising and accel testing. Even though you may not feel it, the mixtures may lean or richen out and that may suggest that some larger or smaller secondary jets may be needed. Data logging will allow you to go home and sus out whats going on without fear of having a crash whilst driving, checking this, looking at that etc.

Get to it..have fun