I am not much of a gear head, but don't mind trying to do things myself. I would like to know if anyone can recommend a good book or even better, a set of step-by-step instructions (preferably with some pictures/diagrams) on how to properly tune a carbureted small block Chevy motor. I would like to know how to adjust timing, carburetor, etc. to get the most kick out of my car. Please assume I know nothing at all (not far off) about any of this stuff.

Here is what I can tell you about what I have:

ZZZ-350 crate motor from ~1987 time-frame
Larger CAM (specs not known) -- lopes pretty good
A/C Delco HEI Ignition (came with the motor)
Demon 650-CFM (crate-tuned) carb (out of the box -- no modifications)
Carb has electric choke and mechanical secondaries
Mechanical fuel pump (stock?)
Factory exhaust manifolds
2.5" exhaust (no X or H pipe) with Flowmaster 30-series mufflers
TH-350 Transmission with 2600 stall
GM 12-bolt rear with 3:73 gears (non-posi)

The car seems to be running rich right now, but has an occasional 10-15 rpm surge at idol (in gear with my foot on the brake) after it warms up. Leaning it out some makes the condition much worse. I very seldom get the car to kick-down by its self when getting on the gas hard, but can manually downshift with good results. I live in Colorado (~5600 feet elevation).


As always, I truly value the knowledge and willingness to help that the experts here so freely share.

Dave

Dave,

you need to find out where your timing is at idle, where it starts to advance and what it does as the RPMs go up. At your elevation things will be a little different than usual but nothing radical. A few degrees, a couple jet sizes. get a good timing light with a dial and a vacuum gauge first, we'll walk through the steps.

Do you have or know anybody who has a wide-band O2 meter?

Dave,

you need to find out where your timing is at idle, where it starts to advance and what it does as the RPMs go up. At your elevation things will be a little different than usual but nothing radical. A few degrees, a couple jet sizes. get a good timing light with a dial and a vacuum gauge first, we'll walk through the steps.

Do you have or know anybody who has a wide-band O2 meter?

Thanks Tom,

I have a fairly good digital timing light (paid ~$100.00 -- not quite sure how to use it yet). I also bought a basic vacuum gauge. I had the car tuned at a general fix-it shop after I put the new carb on it, and I was told they set the timing 12*. I don't know what a wide-band O2 meter is, but assume it's used to measure the air flow???

Dave

it's used to measure the oxygen content of the exhaust, tells the story on the A/F ratio, allows to quickly center in on the right jets and whatnot for the carb.

Do you have a tach you can see from under the hood? basically what we want to do is pull the air filter so you can get at the carb, disconnect any vacuum line to the dist, check the timing at idle. then speed it up until the timing mark starts to advance, note that RPM. then speed it up to 3000 or wherever the mark reaches it's max, probably 3-4000RPM. note the RPM and the number of degrees. let it idle back down, hook up the vacuum advance, re check the total at the RPM it was at before, 3000 or whatever. Write this stuff down as you go along, post it here. We'll see where you're at and where you might want to go.

Do you ever hear spark knock?

the best thing to do is to start hanging out with people that know what they are doing, and have them show you what to do. coming here to ask questions can be helpful, but actually having someone that can show you what to do is so much better. i had my grandpa and dad to learn from. they never rally "taught" me anything, but i sure learned a lot from just being around them.
or, you could just start turning screws and see what happens when you do each thing.

it's used to measure the oxygen content of the exhaust, tells the story on the A/F ratio, allows to quickly center in on the right jets and whatnot for the carb.

Do you have a tach you can see from under the hood? basically what we want to do is pull the air filter so you can get at the carb, disconnect any vacuum line to the dist, check the timing at idle. then speed it up until the timing mark starts to advance, note that RPM. then speed it up to 3000 or wherever the mark reaches it's max, probably 3-4000RPM. note the RPM and the number of degrees. let it idle back down, hook up the vacuum advance, re check the total at the RPM it was at before, 3000 or whatever. Write this stuff down as you go along, post it here. We'll see where you're at and where you might want to go.

Do you ever hear spark knock?

I'll try to get the numbers together over the next day or so -- got to wait for the snow to stop and the temp to warm up a bit. My timing light shows RPM in one of its displays, so getting the readings should be simple enough. On the spark knock, I don't believe that I have an issue there. I'd say it seems pretty smooth/quiet under the hood when the engine is running (no odd noises). I assume the knock you are referring to would be fairly obvious?

Thanks,
Dave

Good advice so far. If you want to read up on all of this and properly educate yourself a big Chilton's book is in order. I go through my "big book" ocassionally just to stay refreshed. Excellent books.

the best thing to do is to start hanging out with people that know what they are doing, and have them show you what to do. coming here to ask questions can be helpful, but actually having someone that can show you what to do is so much better. i had my grandpa and dad to learn from. they never rally "taught" me anything, but i sure learned a lot from just being around them.
or, you could just start turning screws and see what happens when you do each thing.

I wish I could. My Dad is 1300 miles away in California, and I work with a bunch of electrical engineers (you know the white shirt and pocket protector-type). There are a few car guys I know from my car club, but most live 30-80 miles from me, and are only acquaitnences. I learn fast, but just need a jump-start from those that can take the time to talk me through it.

Dave

Good advice so far. If you want to read up on all of this and properly educate yourself a big Chilton's book is in order. I go through my "big book" ocassionally just to stay refreshed. Excellent books.

Is the book something common at the parts stores? What is its title?

Thanks,
Dave

I wish I could. My Dad is 1300 miles away in California, and I work with a bunch of electrical engineers (you know the white shirt and pocket protector-type). There are a few car guys I know from my car club, but most live 30-80 miles from me, and are only acquaitnences. I learn fast, but just need a jump-start from those that can take the time to talk me through it.

Dave

I completely know where you're at man. Any questions you have, just ask right here and between the several thousand of us we should be able to walk you through just about anything.

Is the book something common at the parts stores? What is its title?

Thanks,
Dave

Many parts stores will have the Chilton's books which will either be vehicle-specific softbound books or the big hardbound books that cover a range of years and makes. I prefer the big hardbound ones because they are usually more detailed and include a lot more information. The local libraries usually have these books as well.

when dealing with a modified car, the specs and procedures in a Chilton's manual are almost useless for tuning up a car.
the bigger the cam goes compared to stock, for example, the less idle vacuum it's going to make, and the richer it's going to need to run. it's also going to need more timing at idle to make it livable, as well as a higher idle speed than stock.
if you need a basic education about the inner workings of the 4 stroke internal combustion engine, got to www.howstuffworks.com and read up on it there. the article on engines is very well done.
where are you located? there's probably someone on here that's fairly close to you that can help in person sometime. hell, if you were within about 40 miles of me, i'd come play with your car if you bought me lunch..

when dealing with a modified car, the specs and procedures in a Chilton's manual are almost useless for tuning up a car.
the bigger the cam goes compared to stock, for example, the less idle vacuum it's going to make, and the richer it's going to need to run. it's also going to need more timing at idle to make it livable, as well as a higher idle speed than stock.
if you need a basic education about the inner workings of the 4 stroke internal combustion engine, got to www.howstuffworks.com (http://www.howstuffworks.com) and read up on it there. the article on engines is very well done.
where are you located? there's probably someone on here that's fairly close to you that can help in person sometime. hell, if you were within about 40 miles of me, i'd come play with your car if you bought me lunch..

Derrick,

Thanks for the link. I've bookmarked the write up on the internal combustion engine that you recommended, and will read through it this week. I'm located between Aurora and Centennial, Colorado in a little area of unincorporated Arapahoe County (South-East suburbs of Denver).

Dave

Many parts stores will have the Chilton's books which will either be vehicle-specific softbound books or the big hardbound books that cover a range of years and makes. I prefer the big hardbound ones because they are usually more detailed and include a lot more information. The local libraries usually have these books as well.

Is something like this good?

http://cgi.ebay.com/Chiltons-Auto-Repair-Manual-1980-Hard-Cover_W0QQitemZ7041627615QQihZ014QQcategoryZ2228QQ rdZ1QQssPageNameZWD1VQQcmdZViewItem

I know my particular car won't be referenced in this book, but if there good information that spans small block Chevy V-8's, then I would like to pick one up for reference.

Dave

You probably won't learn much about your car in that book. If you want to learn about small block chevys, order these books and it will get you well on your way.

1. How to rebuild small block Chevy (http://cgi.ebay.com/HOW-TO-REBUILD-YOUR-SMALL-BLOCK-CHEVY-BOOK-NEW_W0QQitemZ320101079314QQihZ011QQcategoryZ378QQr dZ1QQcmdZViewItem)

2. How to build horsepower (http://cgi.ebay.com/HOW-TO-BUILD-HORSEPOWER-BOOK-NEW_W0QQitemZ320101051621QQihZ011QQcategoryZ378QQr dZ1QQcmdZViewItem)

3. Max performance on a budget (http://cgi.ebay.com/HOW-TO-BUILD-MAX-PERFORMANCE-CHEVY-SMALL-BL-BOOK-NEW_W0QQitemZ320101034007QQihZ011QQcategoryZ378QQr dZ1QQcmdZViewItem)

4. How to build horse power 2 "Carbs and intakes" (http://cgi.ebay.com/ebaymotors/HOW-TO-BUILD-HORSEPOWER-Volume-2_W0QQcmdZViewItemQQcategoryZ33615QQihZ008QQitemZ1 80104485957QQrdZ1)


These are some really good books to get you started. Plenty pics and illustrations, good directions, and a good break-down on how parts work.

"How to hotrod the small block chevy" a very old book, parts mentioned are obsolete but what this book is really good at is helping form the attitude or mindset for hotrodding engines successfully. Read it carefully, notice the authors thinking patterns, learn much.

You probably won't learn much about your car in that book. If you want to learn about small block chevys, order these books and it will get you well on your way.

1. How to rebuild small block Chevy (http://cgi.ebay.com/HOW-TO-REBUILD-YOUR-SMALL-BLOCK-CHEVY-BOOK-NEW_W0QQitemZ320101079314QQihZ011QQcategoryZ378QQr dZ1QQcmdZViewItem)

2. How to build horsepower (http://cgi.ebay.com/HOW-TO-BUILD-HORSEPOWER-BOOK-NEW_W0QQitemZ320101051621QQihZ011QQcategoryZ378QQr dZ1QQcmdZViewItem)

3. Max performance on a budget (http://cgi.ebay.com/HOW-TO-BUILD-MAX-PERFORMANCE-CHEVY-SMALL-BL-BOOK-NEW_W0QQitemZ320101034007QQihZ011QQcategoryZ378QQr dZ1QQcmdZViewItem)

4. How to build horse power 2 "Carbs and intakes" (http://cgi.ebay.com/ebaymotors/HOW-TO-BUILD-HORSEPOWER-Volume-2_W0QQcmdZViewItemQQcategoryZ33615QQihZ008QQitemZ1 80104485957QQrdZ1)


These are some really good books to get you started. Plenty pics and illustrations, good directions, and a good break-down on how parts work.

"How to hotrod the small block chevy" a very old book, parts mentioned are obsolete but what this book is really good at is helping form the attitude or mindset for hotrodding engines successfully. Read it carefully, notice the authors thinking patterns, learn much.

Thanks guys -- I'll look for them tonight.

Dave

Let me give you the basics (provided engine is in good shape, good plugs/wires etc).

Set total timing to 36* . To do this disconnect vac advance line and plug. Rev motor till you see the advance STOP advancing and turn the distrib till you have 36*. I suggest briefly running the motor to ~4500-5000 rpms to make sure the advance is all in. You dont want to set it at 36* not knowing that there is more advance left!!! We would like to see that 36* fully in around 3000-3500 rpms. Real handy to have a remote tach where you can see it. Let the engine idle and just make a note where your initial is, probably will be around 16* (most distrbs have a 20* curve, so 16*+20* = the 36* total. Hook up your vac advance line to either manifold or ported vac, whichever your motor idles better with. My motor gets an additional 1-2" of vaccum at the same rpm w/manifold vacuum advance. With the line connected, watch that the vac can doesn't add more than ~12* of advance. With this hooked up, your idle rpm will show around 28* (16+ ~12 = 28) and make for a nice smooth idle and lower engine temps.

Now with that done, warm engine fully and hook up a vacuum gauge to a full manifold port (I'm tee'd into my vac advance line). Set your mixture screws about 1.5 turns out. Watching the gauge for the highest most stabil reading, turn each screw in/out a 1/4 at a time and watch the gauge. Give the engine a few seconds to stabilize. Once you have it narrowed down within a 1/4 turn, give it an 1/8 in either direction for the finial setting.

Then you can move onto the carb. I like to keep dropping my primary jetting 2 steps at a time until the engine developes a stumble/miss/hesitation and then bring up the jets a size or 2 till it clears.

This makes for some clean plugs and a cleaner running car.

Secondary jetting is more of a PIA. Seat of the pants or 1/4 mile MPH is really the only way to do it IMO. But when you get used to your car, the seat of the pants method works pretty good b/c you'll be able to sense small changes.

it's used to measure the oxygen content of the exhaust, tells the story on the A/F ratio, allows to quickly center in on the right jets and whatnot for the carb.

Do you have a tach you can see from under the hood? basically what we want to do is pull the air filter so you can get at the carb, disconnect any vacuum line to the dist, check the timing at idle. then speed it up until the timing mark starts to advance, note that RPM. then speed it up to 3000 or wherever the mark reaches it's max, probably 3-4000RPM. note the RPM and the number of degrees. let it idle back down, hook up the vacuum advance, re check the total at the RPM it was at before, 3000 or whatever. Write this stuff down as you go along, post it here. We'll see where you're at and where you might want to go.

Do you ever hear spark knock?

Okay guys -- here are the numbers (if I read every correctly):

Initial idol RPM = 775 (car at normal running temp [~180 degrees] and in park)
Initial timing with advance disconnected and plugged = 9* (read off the timing mark with timing light advance at 0)
Marks started moving as soon as I started to throttle up
Total advance is at 26* and came in at around 2600 RPM (got this number by pressing the advance button on my timing light until the mark stabilized at 0 at around 2600 RPM and up).

Reconnected the vacuum to the distributor and got the same numbers as before. :confused:

I have my vacuum advance plugged into the front-most vacuum port on the Demon 650 carb.

Thanks,
Dave

Okay guys -- here are the numbers (if I read every correctly):

Initial idol RPM = 775 (car at normal running temp [~180 degrees] and in park)
Initial timing with advance disconnected and plugged = 9* (read off the timing mark with timing light advance at 0)
Marks started moving as soon as I started to throttle up
Total advance is at 26* and came in at around 2600 RPM (got this number by pressing the advance button on my timing light until the mark stabilized at 0 at around 2600 RPM and up).

Reconnected the vacuum to the distributor and got the same numbers as before. :confused:

I have my vacuum advance plugged into the front-most vacuum port on the Demon 650 carb.

Thanks,
Dave


Timing is about 10 degrees to low. That's why you're having carb troubles. Put you some new butterflies back in there to replace the one's you drilled out.

The vacuum advance canister is (1) Busted and needs replacing. -or- (2) It's adjustable and turned all the way off.

Timing is about 10 degrees to low. That's why you're having carb troubles. Put you some new butterflies back in there to replace the one's you drilled out.

The vacuum advance canister is (1) Busted and needs replacing. -or- (2) It's adjustable and turned all the way off.

The carb is new -- nothing modified, so the butterflies should not be an issue. How do I change the vacuum pot on the distributor? Is this something that can be done with a part from my local parts stores, and without any major surgery? Will a vacuum gauge tell me if I am getting vacuum out of the port on the carb?

Thanks,
Dave

vacuum gauge will tell you.

What about this? "Total advance is at 26*..." Clarify, 26 + 9 or 26 all together? Also, I'm concerned that your advance is coming in too soon and may cause pinging problems. the advance shoul;d not start until about 1000RPM, all in at 3000.

Use a piece of vacuum hose, just suck on the vacuum advance, see if it holds vacuum. on the carb, you should be able to feel vacuum at the port or hose connected to the port, either at idle or RPM or both. If the vacuum advance is not leaking pop the distributor cap and see if the mechanism moves when you apply vacuum.

I've never seen an HEI that is set up like yours seems to be. They normally have 25* advance and are slow to come in.

The carb is new -- nothing modified, so the butterflies should not be an issue. How do I change the vacuum pot on the distributor? Is this something that can be done with a part from my local parts stores, and without any major surgery? Will a vacuum gauge tell me if I am getting vacuum out of the port on the carb?

Thanks,
Dave


I'm sorry, I was thinking of a completely different post about the carb troubles.

The vacuum gauge should read vacuum if hooked to the port. Either at idle and/or above idle.

The vacuum can is easily changed by removing the distributor cap and rotor. There are a couple screws that hold it in and the rod slides into a small hole.

He's probably just connected to a ported vacuum source.

Contrary to what Tom said, all the HEI I messed with have either a 20 or 22* curve, so if he had 9* initial + 20 = 29*...he may be reading the mark a little incorrectly, but its not out of the ballpark. Either way, he needs to crank more timing in there.

As soon as you hook your can to a full manifold vacuum source, you should see your timing jump up a good amount.

contrary to what Vince said, the thoudand or so HEIs I've had on distributor machines usually had 25-26* if they were working properly and didn't have a cheapie rotor interfering with the advance weights. He's entitled to his opinion and so am I. Ain't the net wonderful?

anyway, if you're sure it has 9* initial and 26 total mechanical you could advance it 8* no sweat. This will speed up your idle, allow backing off the idle speed screw on the carb. However, I still see the advance coming in too soon as an issue, may cause pinging. After driving it a little with new advanced timing see if it wants to ping. If it does it'll have to be fixed.

Tom and Vince,

He stated in the first post that this was a ZZZ with the original distributor. Here are the specs directly from the GMPP Install guide.

http://www.chevelles.com/showroom/data/500/DizzySpecs.jpg

I have visually confirmed these with a good dial back light and also traded e-mails with Dave Ray who seems to have a lot of knowledge re: HEI distributors. If the timing is set per factory specs, it should be 10 initial 32 mehcanical and a huge 52 total w/ vacuum. My ZZ4 pinged like crazy with these settings. I am now running a MSD Pro-Billet with the curve set to deliver 21 mechanical all in at approx. 3100 to 3200 RPM (for a total of 32 with 11 initial) and the supplied MSD vacuum advance gives me 10 vacuum advance. Per Dave's guidance, I may bump the timing up a couple of degrees, but the 350 H.O. engines (ZZZ-ZZ4) do not really like 36 a whole lot. If the gas is the least bit marginal, you will have serious part throttle pinging. Ask me how I know :clonk:.

Tim, I have that same dizzy, and yes its a 22* curve (which sucked for me cause I want 36*, which means a 14* initial - yuck!).

I had to modify the distributor for a 14* mechanical curve. Now I run 22* initial, 36* total. I used the same 20* can and put a zip tie on it to limit the vac advance to about 12*, so my cruise timing is 48*.

I forgot that the new crate motors like less timing. Thsi is bad b/c if you want 32*, that means initial will be 10* - yuck again!

Yep, it's high and what's worse is how long it takes to get it all in. FWIW, Dave Ray recommends using full manifold vacuum, not ported, so the low initial mehcanical is not so terrible.

The MSD Pro-Billet works great in my car, and the thing is a beast for a heavy car with a small engine. Not Big Block beast, but it puts a big smile on my friends (or huge eyes for those who are not expecting it).

vacuum gauge will tell you.

What about this? "Total advance is at 26*..." Clarify, 26 + 9 or 26 all together? Also, I'm concerned that your advance is coming in too soon and may cause pinging problems. the advance shoul;d not start until about 1000RPM, all in at 3000.

Use a piece of vacuum hose, just suck on the vacuum advance, see if it holds vacuum. on the carb, you should be able to feel vacuum at the port or hose connected to the port, either at idle or RPM or both. If the vacuum advance is not leaking pop the distributor cap and see if the mechanism moves when you apply vacuum.

I've never seen an HEI that is set up like yours seems to be. They normally have 25* advance and are slow to come in.

I'm not sure, but here is exactly what I did to read the numbers.

1. Connected my timing light per instructions and read the mark at idol. Read 9* directly off the timing mark.

2. Revved up and the mark went up off the timing marks, so I started to press the advance button on my light until the mark was at 0 (the light read 26). So, it very well could be 26 + the initial 9 (35*).

Does this seem correct? Is there a better way to use the light to get the right numbers? Should I use the lights advance button to move the marks at idol until they read 0 first, then rev the motor and advance again until the marks are at 0?

Again, I just want you all to know how much I appreciate your patients and the time you are taking to explain things for me.

Dave

you're fine on the reading part. it has 26 total mechanical, that includes the 9* initial. From the other info posted here it seems the dist is not too happy. or something else has happened because the advance numbers don't match up at all with the chart kindly posted by Tim up above. No part of it matches up up or is even close, implying the dist is hosed up or it's not the dist it's supposed to be. There's not enough advance occurring and what it does have is coming in a way too low RPM. Meanwhile, bump your initial up to 18* or so, see if it turns into a nasty pinger. Try the increased initial and see what happens. Post back here with results.

Key to success here is to go slow, do one thing at a time so as not to get lost in too many changes.

If you are going to use the dial for total timing referenced to 0 degrees on the balancer, it would be a little better (IMHO) to do the same for your initial. In otherwords, either put a timing tape on the balancer so you can see your total there with the light set to zero, OR always read from the TDC mark on the balancer and use the dial feature of the light to read the timing.

You didn't say what RPM you are at when you are reading 26. Over 4000 RPM is going to sound like a ton of revs when you're hovering over the front of the engine sitting in the garage. Does your timing light also show RPM? If so, make sure you get it above the number posted on the chart. You don't have to hold it there for very long, just long enough to read the light. Even if it does read more, I think common wosdom says that the stock distributor brings in the mechanical too slow. As I stated earlier, somewhere between 3200 and 3400 RPM should get you full mechanical. You can experiment with lighter springs once you get the incorrect total figured out.

Also, I do not recall if anyone asked if you had another light to just make sure that your timing light is reading accurately? You just never know. Having said that, I think you for sure have something wrong with your distributor.

... You didn't say what RPM you are at when you are reading 26. Over 4000 RPM is going to sound like a ton of revs when you're hovering over the front of the engine sitting in the garage. Does your timing light also show RPM? If so, make sure you get it above the number posted on the chart. You don't have to hold it there for very long, just long enough to read the light. Even if it does read more, I think common wosdom says that the stock distributor brings in the mechanical too slow. As I stated earlier, somewhere between 3200 and 3400 RPM should get you full mechanical. You can experiment with lighter springs once you get the incorrect total figured out.

Also, I do not recall if anyone asked if you had another light to just make sure that your timing light is reading accurately? You just never know. Having said that, I think you for sure have something wrong with your distributor.

I was at ~2600 RPM when I read 26*. I took it up to about 3500 with no more advance, but did not go near the 4600 shown on the chart that you posted (thanks Tim). So, it sounds like maybe I should go back and look at my initial numbers again, and make sure I get above the 4600 RPM mark before I start to make any adjustments. I'll try to get that done tomorrow before we get our next big storm (possible 12 inches of snow on the way). I'll be out of town Sunday-Wednesday on business, so my window of opportunity is narrowing.

Dave

If you went from 2600 to 3500 with no change in timing, then there is definitely something amiss here. You should see a fairly steady increase in timing all the way from where it starts to advance to where it maxes out at whatever RPM the curve is designed for. A thousand RPM without any additional advance tells me you need to dig into that distributor and figure out what's not working right.

sounds like it has a broken or missing spring on the advance mechanism. at least, that would account for the early start and the low RPM of the total.

Dave, do you know how to pull the distributor cap and rotor? the advance weights and springs are right under the rotor and plainly visible.

might be able to see why the advance curve is so short, maybe a piece of something is jammed in there or something along that line. used to problems with cheap rotors interfering with movement of the advance weights.

For some reason, my ZZ dizzy had the curve start REALLY early, like just off idle. Didn't match up to what that chart said. It would start advancing probably around 800 rpms. I actually had to put one or two stronger springs in there to get a stable idle. Seems like that dizzy would work good if you were idling arounf 600-650 rpms. If you can take a picture of the springs I can tell you if I had the same in mine.

I remember my curve coming in around 2600 rpms actually now that I think about it, so I think his readings are correct.

My dizzy was new BTW.

For some reason, my ZZ dizzy had the curve start REALLY early, like just off idle. Didn't match up to what that chart said. It would start advancing probably around 800 rpms. I actually had to put one or two stronger springs in there to get a stable idle. Seems like that dizzy would work good if you were idling arounf 600-650 rpms. If you can take a picture of the springs I can tell you if I had the same in mine.

I remember my curve coming in around 2600 rpms actually now that I think about it, so I think his readings are correct.

My dizzy was new BTW.

Your experience makes me wonder if they changed the distributor and/or curve from the ZZZ to the ZZ4. I couldn't find any reference anywhere to this, but it wouldn't surprise me at all. I know the chart is dead on for mine, but the ZZZ was quite a few years earlier and there were plenty of changes from then to now.

Dave, do you know how to pull the distributor cap and rotor? the advance weights and springs are right under the rotor and plainly visible.

I'm not sure (don't laugh) -- any tips would be welcome, as I don't want to break anything.

If anyone is interested, I found a cool document that describes all the parts Chevrolet shipped in each of the ZZZ-ZZ4 crate packages. I've linked it to my web page if anyone wants it.

http://home.comcast.net/~dcabral99/Downloads/SB_zzengine.pdf

Dave

Mine is a new ZZ4, I don't recall exactly how it was but nothing like the off idle advance, short steep curve discussed here.

Thanks Dave. It's the same chart GM has in the Performance Parts catalogs, but with a few additions. I don't think too many guys have one just sitting around and it's nice to see what's been kept the same, etc.

Mine is a new ZZ4, I don't recall exactly how it was but nothing like the off idle advance, short steep curve discussed here.

I have the same experience as you Tom. Mine took forever to come in, and with the HUGE amount of vacuum advance, part throttle ping sounded like a bunch of BBs in a tin can. Until I switched to the MSD, I unplugged the vacuum advance so I could drive it without all the pinging. Now, I don't have any, and am going to experiment with adding in a couple more degrees.

I do find it interesting that some of the experiences seem to be all over the place, the distributor P/N is the same from ZZZ all the way through ZZ4

Dave, do you know how to pull the distributor cap and rotor? the advance weights and springs are right under the rotor and plainly visible.

might be able to see why the advance curve is so short, maybe a piece of something is jammed in there or something along that line. used to problems with cheap rotors interfering with movement of the advance weights.

I figured out how to remove the cap, but am not sure about the rotor. It looks like I should just need to remove the two screws on either side of the rotor? Anything else I need to be aware of before I proceed?

I took some pictures of the distributor with the cap removed. Click this link to see them. (http://pictures.aol.com/galleries/dcabral99)

Dave

yes, pull the two screws out, the rotor will come off easily. note which way it's pointing, but it will only go on one way anyhow.

take a pic of the top after the rotor is off.

yes, pull the two screws out, the rotor will come off easily. note which way it's pointing, but it will only go on one way anyhow.

take a pic of the top after the rotor is off.

Okay -- I added a couple of pictures with the rotor removed. Click this link to see them. (http://pictures.aol.com/galleries/dcabral99) The weights and springs seem pretty rusty?

Dave

looks like there's both springs. yes it's pretty nasty looking. the crossbar piece that the rotor was bolted to - grab it by the ends, twist it. it should only go one way, then let go. it should pop back to where it was. if it moves back slow ot sticks it's messed up.

can you take a pic as it is, then from the same camera position use a finger to push it to full advance, take another pic so I can see how far it moves?

Look at the inside of the rotor, can you see any traces of rubbing? like the rotor rubbing on the parts of the advance mechanism, interfering with its' travel? Also, try to figure out hoe to say this in writing, look at the sides of the inside, you might be able to see where the weights have been coming out and hitting the rotor, again limiting the travel.

look, see, feel, bare hands diagnostics. :)

looks like there's both springs. yes it's pretty nasty looking. the crossbar piece that the rotor was bolted to - grab it by the ends, twist it. it should only go one way, then let go. it should pop back to where it was. if it moves back slow ot sticks it's messed up.

can you take a pic as it is, then from the same camera position use a finger to push it to full advance, take another pic so I can see how far it moves?

Look at the inside of the rotor, can you see any traces of rubbing? like the rotor rubbing on the parts of the advance mechanism, interfering with its' travel? Also, try to figure out hoe to say this in writing, look at the sides of the inside, you might be able to see where the weights have been coming out and hitting the rotor, again limiting the travel.

look, see, feel, bare hands diagnostics. :)

Hello Tom,

I took two more pictures (one not advanced, and one advanced). Click this link to see them. (http://pictures.aol.com/galleries/dcabral99) After advancing the assembly, I let it go, and it snapped back to its original position with no drag or hesitation. There is no sign of any rubbing inside the rotor, but the contacts inside the cap seem to look a little corroded (not bad, but noticable powdery film). I'm wondering if I should just plan to replace the distributor based on the age and condition of the parts?

Dave

you could, it's certainly not working right as far as the advance goes. Trouble is, the OEM distributor is not designed for easy adjusting. Why don't you look at Summit or wherever you shop for this stuff, see what's available. I'd recommend you stick with the HEI style dist, coil in cap, self-contained. I think all the major vendors have something suitable.

like this or similar:
http://store.summitracing.com/egnsearch.asp?N=400249+304998

or this:
http://store.summitracing.com/partdetail.asp?autofilter=1&part=MSD%2D8362&N=700+400122+318958+115&autoview=sku

you could, it's certainly not working right as far as the advance goes. Trouble is, the OEM distributor is not designed for easy adjusting. Why don't you look at Summit or wherever you shop for this stuff, see what's available. I'd recommend you stick with the HEI style dist, coil in cap, self-contained. I think all the major vendors have something suitable.

Can anyone make a recommendation on what would give me the best overall street performance (I don't race the car, but like to get on it every once in a while). I don't mind spending a little more money if there is a need, but don't want to buy way more than I need either. Ease of installation and setup are also important factors I'd like to take into consideration. I have purchased from Summit before and like the way they do business, so I'd lean in their direction if the recommended item is carried by them.

Edit: Tom, you beat me to the punch and answered my question before I even had a chance to ask it.

Thanks,
Dave

Does anyone have an opinion on this distributor?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270108516432&fromMakeTrack=true&ssPageName=VIP:watchlink:top:us

Should I just go with something like MSD and stay away from the low-cost stuff?

as soon as I see this kind of stuff I know they are BS artists:
"CNC MACHINED SHAFT: the Procomp HEI has a beautiful CNC machined POLISHED to a mirror finish HEI distributor shaft. It is also at least 50% thicker than competitors shafts."

If it's not the same size as all the other shafts standard parts wouldn't fit on it. there's really only 2 sizes, .490 and .500. WHat you have there is the usual China junk. Should be marketed through Wal-Mart.

Before spending the dough on a new distributor, try a different curve:

http://store.summitracing.com/partdetail.asp?part=MRG%2D929G&autoview=sku (http://store.summitracing.com/partdetail.asp?part=MRG%2D929G&autoview=sku)

It might be worth the $8 bucks.

I have this in my small block with the lightest springs, initial is 16° and 36° total at 3k rpm (20° mechanical advance). It does not start advancing until 1k rpm. Click on the installation instruction to see the different curves you can set up by changing included springs.

You probably will have to setup the curve for a new distributor anyway.

as soon as I see this kind of stuff I know they are BS artists:
"CNC MACHINED SHAFT: the Procomp HEI has a beautiful CNC machined POLISHED to a mirror finish HEI distributor shaft. It is also at least 50% thicker than competitors shafts."

If it's not the same size as all the other shafts standard parts wouldn't fit on it. there's really only 2 sizes, .490 and .500. WHat you have there is the usual China junk. Should be marketed through Wal-Mart.

Thanks again Tom,

I think I will order one of the MSD-8362 (Street Fire HEI) distributors you recommended earlier. It seems like it fits the bill on all of my needs and maybe more. I like the fact that it has an adjustable vacuum advance and that it is basically the same as my GM as far as where everything hooks up -- should make it easier to install (if my firewall doesn't get in the way). Once it's delivered and I get it installed, I will probably come back with more questions on the tuning aspects that I was after when I started this thread.

Dave

Thanks again Tom,

I like the fact that it has an adjustable vacuum advance

I bought the crane adjustable advance can for $30. Unless your distributor is total junk, you can simply swap this component in.

I bought the crane adjustable advance can for $30. Unless your distributor is total junk, you can simply swap this component in.

Matt, Good suggestion. What about one of these kits to replace the works without pulling the distributor itself?

http://store.summitracing.com/partdetail.asp?part=SUM%2D850032&autoview=sku

One question about the wiring -- these kits indicate a 4-pin HEI Ignition module type. Is this unrelated to the wiring plug on the ouside of the distributor? My plug only has three pins on the harness that connects the cap to the base.

Dave

it's unrelated, it's referring to the pins on the module. 4-pin means it's early style, before comptuers in cars came along.

looked at your pic of working the advance by hand, looks OK to me. strange deal.

I'd hesitate to buy that fix-up kit, if something goofy is wrong with your advance mechanism that kit might not fix it.

I just ordered a new MSD Street Fire HEI Distributor. I want to eliminate as many variables as possible. This way I can start out with an understanding of exactly what I have, and that should make it easier to go from there. I'll update this thread once I get the parts. In the meantime, I'll do some reading on installing a distributor -- found a few good references on the web that walk through the process. Seems like a strait-forward thing to do as long as I take my time and follow ALL the steps.

Dave

there's a couple gotchas in the deal, post here when you're ready, there's a couple tips that can make it go real easy.

Your right, a new set-up will eliminate more variables. I was just trying to possibly save you a buck or 2.

Let us know when you get your new parts. Recurving my distributor made the car a whole different animal. I just picked up a vacuum pump/gage so I can further fine tune my vacuum can.

Do you have a vacuum hand pump with a gage? It helps with setting up the vacuum can.

Your right, a new set-up will eliminate more variables. I was just trying to possibly save you a buck or 2.

Let us know when you get your new parts. Recurving my distributor made the car a whole different animal. I just picked up a vacuum pump/gage so I can further fine tune my vacuum can.

Do you have a vacuum hand pump with a gage? It helps with setting up the vacuum can.

I appreciate your suggestions; I just thought it made more sense to start with something known, rather than to continue chasing issues. I do have a vacuum gauge with a hand pump. I bought it along with my timing light. I've got a lot of learning to do, but with the help of those on this site, I should be able to get the job done.

BTW -- I finally got my kickdown cable adjusted correctly based on some information I found searching though old threads, and what a difference that made! The car drives much better already, and it will downshift at 60 mph and hold second gear until 80 mph. Once I get the new distributor installed, the timing adjusted correctly, and my carburetor properly jetted and tuned I'll be a very happy camper.

Dave

My parts are here, and I will attempt to do the install of the new distributor this weekend. The directions provided by MSD seem pretty straight-forward except for the warnings about breaking in the gear. How critical is it to follow the MSD procedure completely on this? For one, I run Mobil-1 synthetic oil in my car, and the break-in notes state not to use synthetic oils during this period. They also say that the distributor should be pulled to check for gear wear after it has been run for a while. Does anyone actually do all this stuff? I don't want to risk damaging my engine, but this stuff seems a bit extreme for a car that will be driven on the streets -- not raced. Any opinions?

Thanks,
Dave

Okay -- the new MSD Street Fire distributor is installed, and I'm ready to learn what to do next to tune the car. Right now the timing numbers look like this:

Vacuum disconnected and plugged:
Initial timing at idol - 16*
Starts to advance at ~1100 rpm
Stops advancing at 36* at around 3200 rpm

Vacuum connected:
Same as above but advances to 40* at around 3400 rpm

By the way, I think I discovered the problem with the vacuum advance on my old distributor. There was a small ball bearing stuck inside the vacuum hose that ran between the distributor and the carburetor. :confused:

Dave

Your mechanical advance looks good.

As for the vacuum advance can, you want to take a vacuum measurement (manifold, not ported) at idle (in gear for an auto trans) and record this value.

Next, use your vacuum hand pump to adjust your vacuum can to fully advance 1" (preferably 2") of vacuum lower than the recorded value above. Example: Vacuum at idle in gear is 10", then set can to fully deploy at 8". This way your idle will not vary and be steady. Hook your vacuum can to a full manifold vacuum port. How much advance does your can put out? You can check by rechecking initial timing at idle and subtracting it from your mechanical initial of 16°. Then add that number to 36°, which would be advance at cruise. I think you want to shoot for 50-52°.

What I descibed above is for full manifold vacuum. You can also experiment with ported vacuum, which has no vacuum at idle. This port is located above the throttle blades. You would have to cruise around with the gage hooked up and monitor vacuum readings.

sounds good. your vacuum advance is a little shy, but that might be able to be adjusted. according to what you posted it has only 4*? Use you hand vac pump and timing light to see what it's capable of producing. The ball bearing in the hose trick shuts off vacuum advance to help with pinging problems.

I wouldn't sweat the distributor gear stuff, you're running a stock or stock-type cam. Mostly that's CYA stuff for them.

BIg question: How does it run?

sounds good. your vacuum advance is a little shy, but that might be able to be adjusted. according to what you posted it has only 4*? Use you hand vac pump and timing light to see what it's capable of producing. The ball bearing in the hose trick shuts off vacuum advance to help with pinging problems.

I wouldn't sweat the distributor gear stuff, you're running a stock or stock-type cam. Mostly that's CYA stuff for them.

BIg question: How does it run?

The vacuum advance is adjustable, and I haven't done anything with it yet. It is supposed to be capable of providing up to 22*. I need to get a reading on the vacuum I'm getting from at the carb, then use the chart provided by MSD to figure out how many turns on the adjusting screw I need to make to get the advance I want. What is a good number to shoot for on the vacuum advance? I see some people talking about 50+ degrees.

The car is running pretty good right now, but won't idle below the high 700's (770-790). I adjusted the idle speed screw as far as it made any difference, and then set the four mixture screws just to the point that the car would idle without dying. After doing this, the car doesn't seem to be running as rich, but also seems to have given up a bit of power as well.

Another related, but less important issue is that my stereo is now cutting out intermittently. I re-routed the amplifier power wire, and still have the problem, but not as bad. I also found a loose crimp connector on the tach wire and fixed that, which also made some improvements. I called MSD, and they recommend checking the ground wire at the coil and possibly running another wire from the ground terminal on the coil to a good ground source.

Dave

the idle doesn't affect the on-the-road power.

Are you still using the sec idle adjustments and complaining about it being rich? I thought we already went through all this?

adjust the vacuum advance to add about 10*, see how it works. Basically, the idea is to run as much as you can without setting up a pinging condition. Set it for 10, see how it goes. if it doesn't ping add 5 more. If it does ping take out five. then you can go back and forth using 3* increments if you have the patience. Use the timing light to verify what you have, don't rely on the paper stuff they send.