69 1111480 distributor

[tom]

Thank you John!

[melav8r]

The VC-1810 is ideal but NAPA tells me it is NLA.

AutoZone sells them as # DV1810, $12 and no additional shipping or freight charges if ordered from a local store. You'll get it in 2-3 business days.

http://www.autozone.com/Ntt,dv1810/shopping/allResults.htm;jsessionid=5E07B3BEBFE00E9E93B1D95A3164F469

[JohnZ]

The now-discontinued NAPA/Echlin VC-1810 vacuum advance unit, stamped "B28", is also available now as GM #88924985, AC-Delco #D1312C, available from GMPartsDirect.com. I bought a bunch of them in November.

[melav8r]

Thanks John, I actually walked into the local AC Delco distributor and gave the D1312C number you provided and the service guy told me I wouldn't see it for about a month. Fortunately I found the AutoZone part number and after I picked up the first one last night and confirmed it was a B28, I ordered a 2nd one which I should have by Saturday for my original 480 which will remain on the shelf even though i completely cleaned and reserviced it including reskinning so it looks great!! oh well. BTW, picked up a small tube of moly grease for the grease well at a local hobby shop for $5.

As for the B28 I picked up last night, stuck it in my DavesSmallBodyHEI this morning which although I specified 6"-8" of idle vacuum when I had Dave build it, he supplied with a B26 can, (VC1808 or same as VC1765/B20). so with full manifold vacuum the engine would hunt around and idle would surge and drop and hunt and... you get the picture. Because of this for the last year, when I put Dave's SBHEI in service,  I've had it hooked up to ported vacuum.
So, like I said, Installed the B28 this morning, reinstalled the distrib, set static timing to 8*, hooked up full manifold vacuum to the can and the car runs great!! Crisp throttle response, stable idle, significantly less to nill gas fumes in the passenger compartment... nuff said!!
So with 8* of initial, total timing @ 3200 rpm is 37*. could probably stand some more initial but runs great and starts right up as set now so there it will stay!!

I know this subject has been beaten and rebeaten over the years but...

[Dave69x33]

JohnZ,

As I understand it, the vacuum choke pull-off is designed to partially open the choke plate when vacuum develops (just after the engine starts), to prevent an over-rich idle.  I believe the pull-off also helps prevent the choke plate from snapping closed under the vacuum draw down thru the venturi (front two primary barrels) until the thermostat choke spring heats up and fully opens the choke.

With your choke pull-off blocked off, do you experience rich fuel starts or problems with the choke plate from closing until it is fully open?

Did you make any other modifications to prevent this condition?

Thanks,

Dave

[JohnZ]

JohnZ, With your choke pull-off blocked off, do you experience rich fuel starts or problems with the choke plate from closing until it is fully open?

Did you make any other modifications to prevent this condition?

Thanks,

Dave

Dave - My choke pull-off isn't blocked off - I'm just sharing its vacuum source for the distributor, using the same tee the production arrangement used for the diverter valve signal hose. That tee came already installed on the carburetor - see UPC 6, Sheet C8, View "A" in the Assembly Manual - you'll see the diverter valve signal hose (item #15) being connected to the tee.

[Dave69x33]

JohnZ,

To clarify - you removed the diverter valve signal hose from this T-fitting and rerouted the distributor vacuum advance hose in its place, correct?

Is your diverter valve signal vacuum hose now inactive, or what did you do with this hose?

Related to this topic, I recall from a previous discussion topic, where some people are now internally modifying the A.I.R. pump (during pump restoration) to defeat its function, yet retain the pump to function as an “idler pulley” to keep a stock look under the hood.  Thus, the diverter vacuum hose would serve no purpose other than for looks.  This hose could be internally blocked off and pushed into its original location. It’s tucked under the air cleaner and not visible to the casual observer.   Then for a “points” show, the two hose can be easily swapped back to their correct locations for judging purposes.

Does this sound feasible?  Am I forgetting anything?

If the A.I.R. pump is defeated but retained as described above, ideally, should the A.I.R. extension tubes be shorten and pinched closed to get them out of the exhaust air flow path?

P.S:  Sorry for belaboring this…this could be another topic.

Thanks in advanced for your input.


 

[mjbake]

Boy I sure enjoy John Z when he answers a question. I'd love to spend a day or two with you just picking your brain, but I'm afraid I couldn't handle it.
Thanks for all the helpful information over the years.

Mike.

[JohnZ]

JohnZ,

To clarify - you removed the diverter valve signal hose from this T-fitting and rerouted the distributor vacuum advance hose in its place, correct?

Is your diverter valve signal vacuum hose now inactive, or what did you do with this hose?

Related to this topic, I recall from a previous discussion topic, where some people are now internally modifying the A.I.R. pump (during pump restoration) to defeat its function, yet retain the pump to function as an “idler pulley” to keep a stock look under the hood.  Thus, the diverter vacuum hose would serve no purpose other than for looks.  This hose could be internally blocked off and pushed into its original location. It’s tucked under the air cleaner and not visible to the casual observer.   Then for a “points” show, the two hose can be easily swapped back to their correct locations for judging purposes.

Does this sound feasible?  Am I forgetting anything?

If the A.I.R. pump is defeated but retained as described above, ideally, should the A.I.R. extension tubes be shorten and pinched closed to get them out of the exhaust air flow path?

P.S:  Sorry for belaboring this…this could be another topic.

Thanks in advanced for your input.


 

Correct - my diverter valve signal hose has a BB in it so it's plugged and inactive whether it's connected to the tee or not. The diaphragm in most diverter valves has failed, and that becomes a massive vacuum leak; in a functional A.I.R. system, a failed diaphragm also defaults the valve to the open position, pumping air into the exhaust system 100% of the time, which causes "afterfiring" or "popping" on overrun. My A.I.R. pump is "gutted" (vanes removed), so it just serves as an idler pulley.

I also removed the extensiion tubes in the exhaust manifolds and replaced them with #10 x 1/2" flat head machine screws; that plugs the holes (to keep hot exhaust gases out of the air manifolds so the hard-to-duplicate finish doesn't get burned off), and the tube nuts on the air manifolds end up in the same position as they did with the extension tubes in place.

With the A.I.R. pump gutted, it'll last forever; the primary failure mode for A.I.R. pumps is galling of the ends of the vanes and the running surface on the housing, which results in seizure of the pump; gutting the pump eliminates the failure mode.

[Dave69x33]

Thanks JohnZ. 

Your recommendation on the A.I.R. pump system is what I was hoping to do as a winter project this year.  The tip to use #10 x 1/2" flat head screws is a good idea to keep the hot gases out of the A.I.R. tubes so they do not discolor.  That and why I was thinking about cutting off the extension tubes and pinching the tips closed, but I like your idea using the screw in place of the tubes.

Thanks again!

Dave

[Pacecarjeff]

John, the screws are ok.
But I would really recommend using 1/8" brass pipe plugs

The manifolds should come off, and this can be done from either the front or the back.
just thread the extension holes and inset the plugs.

Over time your machine screws could deteriorate and may fall into the cylinders.

On the other hand with the brass plug, it becomes fused to the steel, and since the brass is soft metal it could be easily drilled out.
30 years later the brass would still be perfect,  but I would feel funny about a screw hanging there in that hole.

Screws should be temporary -  I don't consider them a permanent solution.

[JohnZ]

John, the screws are ok.
But I would really recommend using 1/8" brass pipe plugs

Over time your machine screws could deteriorate and may fall into the cylinders.
30 years later the brass would still be perfect,  but I would feel funny about a screw hanging there in that hole.

I use stainless flat head machine screws - the angle on the bottom of the screw head matches the flare seat for the extension tube in the manifold perfectly, and they won't corrode/deteriorate.

[Dave69x33]

I wanted to follow up on this discussion forum covering the “B28” vacuum advance and centrifugal advance mapping.  I need tips about recurving my distributor and fine tuning the carb.

My ‘69 302 Z28 is basically stock except with a ’70 LT1 solid lifter cam, flat top pistons, so I estimate my C.R. somewhere between 10 - 10.25:1.  I am using stock exhaust manifolds and exhaust system, and running a 180 degree thermostat.

The distributor is a std. Delco points style distributor converted to Pertonix electronic ignition and Pertonix Flame-Thrower II high output coil.  The distributor was recurved about 10 years ago with aftermarket centrifugal weights and light silver springs, but I don’t know the brand.  I recently changed the vacuum advance unit from a “B1” to a “B28” and mapped the advance curve.  A black advance stop busing is installed limiting centrifugal advance to 24 degrees.

I recently gutted the A.I.R. smog pump and it now functions as an idler pulley and blocked off the air delivery tubes  The vacuum advance hose is now connected to direct manifold vacuum, at the T-fitting located at base of carb were A.I.R. diverter valve vacuum hose was originally connected.

The carb is the stock 780 Holly, List 4053, with 68/76 primary/secondary jets, #85 primary power valve and block off plug in the secondary PV side.  The #85 PV was selected to opening at 8.5” Hg, or about 1” to 1-1/2” Hg below the manifold vacuum reading.  I using the #28 pump discharge nozzle, and the white (weakest) vacuum secondary spring and omitted the check ball.  I run 93 octane pump gas.


Results:
My set-up was with the smog pump active and the vacuum advance connected to the “stock” ported vacuum source, but now connected to full manifold vacuum as stated above.  Initial timing is set at 12 deg. BTDC with a +/- 0.5 degree of flutter with the centrifugal advance secured to not to influence timing.  Idle vacuum is 9 – 10” Hg and idle mixture optimize to maintain 9 - 10” Hg.  The B28 vacuum advance adds about 16 – 18 "crank" deg of advance, which I can adjust with a vacuum timing limiter cam from Crane Cams.  Idle RPM is set to spec., at about 900 RPM.

With the centrifugal advance active, the advance it is coming in too early and causing a jumpy +/- 1.0 deg or more of timing flutter at idle.  The springs are too weak and need to be replaced.  Idle must be adjusted down to 600 RPM to prevent centrifugal advance from coming in.  At 900 RPM, 9 deg’s of advance results, checked with a dial back timing light.  The centrifugal advance map curve yielded the following degrees of advance at the corresponding RPM’s, checked by dialing the timing light back to the 12 deg initial and recording the advance: +9* @ 900, +12* @ 1100, +16* @ deg at 1300, +19* @1500, +22* @ 1700, and all in at  +24* @ 1900.  Thus total advance of 36 deg (12 init. + 24 cent.) is all in by a very early 1900 – 2000 RPM.  The overall advance totals 54 deg at cruise conditions, adding the 18 deg of vacuum advance. I may limit vac advance to 16 to get overall advance down to 52 deg.  I fear engine ping or detonation during the hot summer season.

Throttle response is noticeably better. During aggressive 1st, 2nd, or 3rd gear acceleration runs, the 302 power really pulls hard after 3000 – 3500 RPM to redline.  At this point I can not tell if the power band is natural to my engine, the current distributor timing map, or the mapping of the Holley carb jets and secondaries.  While in park and idling, stabbing the throttle to wide open, there is occasional lean condition back fire thru the carb, but otherwise no noticeable stumble.  Changing the Holley primary jets from 68 to 72 will hopefully cure this lean back fire.

Questions: 
If the goal is to have a weight/spring combination that does not come on too early, but is “all in” by 2800 – 3000, what is a recommend source for centrifugal weights and springs? 

What color spring or spring combination and advance map is recommended, or found to be ideal in the 302? 

The MSD Ignition web-site does a good job showing various advance curves with their distributor, limit bushings, and spring combinations but I am not sure if or how this translates to my stock distributor.  I have read mixed results about the quality of aftermarket weights, and recommendation to stay with GM weights.  I am not having much luck finding advance bushing and advance kits locally for the old style points distributor.

What Holley Carb vacuum secondary spring is recommended?

Should the vac secondary check ball be retained or omitted?

My goal is to find the combination of parameters for the ignition and carburetor yielding optimum performance and drivability, yet retain the stock look of my 302.

Please excuse my long discussion but I suspect there are others with my same questions and goal in mind, yet have experimented with a set-up that has yield good results.

Thanks and your recommendations will be appreciated!

[JohnZ]

Excellent post, lots of good info to work with! 

Unless you've modified the carb base gasket, the vacuum port on the passenger side of the base of the 4053 carburetor is a "ported" vacuum source; that's why my "driving" setup uses the tee in the rubber hose from the front of the carb base to the choke pull-off diaphragm for the vacuum advance, which is a full manifold vacuum source (and that's where the diverter valve signal hose was connected from the factory, not the port on the carb base).

The #85 primary power valve is incorrect, and is too close to the idle vacuum signal - it should be a #65, and you should have a #85 in the secondary instead of a plug; that's the stock setup, and it works.

Put the check ball back in the secondary diaphragm housing - omitting it causes the secondaries to "slam" open instead of responding in a linear fashion to the airflow in the venturis.

I run the stock secondary diaphragm spring, works fine for me.

Get those #68 primary jets changed out to 72's and you'll feel the difference.

24* centrifugal in the distributor is on the money, but 1900 rpm "all in" is too soon, as is 600 rpm for the starting point of the curve. You can't buy a "spring kit" off the shelf that will accomplish what you want - yank the distributor and give it to a shop with a Sun machine (or send it to Jerry MacNeish) and have them set up the curve you want (start @ 1000-1100, "all in" by 3000).

[69Z28-RS]

this thread began with a question about the vacuum advance pod for the 480 distributor.  Reading the thread got me interested in following up and rebuilding my 480 distributor, so I bought a couple of the autozone PN's mentioed, and ordered a GM part (but haven't got it yet).  When I disassembled my distributor, I think it had the original vacuum module on it (see photo below); can someone confirm this is the original?  or at least the original PN?

...  after removal, I compared the spring strength to the new autozone part, and find that the original spring tension is roughly 3-4 X more than the new autozone part...    which concerns me.   Is this normal?  Wouldn't it require a lot more vacuum to affect a timing change wiht a high spring pressure?  What gives?   IS the autozone part I have too 'different'?  Or is there some kind of failure of the original part that could cause this?   Yes, I'm totally confused.  There appears to be a slight bend in the original; could this cause the stronger spring/diaphragm pressure?

I'm posting side by side photos of the two parts below in soliciting your responses and comments...



I would also like to confirm that this is the original advance plate for the 480 distributor; I pulled this distributor from my car in the 70's (it was sloppy) when I rebuilt the engine and used a rev pol distributor; it's been laying under my bench since until I retrieved it to rebuild it.