292 y-block distributor puzzler

[highcking]

I recently determined that the dual vacuum retard/advance unit on my ‘56 Fairlane was no longer working. I have an NOS spare that I tested and installed today. Tricky to do on the car but it came out ok. Went to start — no dice. Car behaves like the timing is way off. I did not move the distributor, and reused the same cap and rotor. I did remove the plug wires but reinstalled them using the “1” stamped on the cap and the clockwise firing order stamped on the block. If I crank the motor to TDC, it looks like the rotor is pointing to the #1 plug wire.

What gives? The shop manual is not helpful. I thought of rotating the distributor a bit - but how do you do that with two steel vacuum lines attached? I also tried rotating the plus wires one position at a time and that did not help. Car started instantly before. What am I missing? Should I surrender and go with an updated distributor?

Bill in Virginia

[scicala]

To start with, I think you said you put the plug wires on the cap for clockwise rotation. Y-Block V8's were counter-clockwise distributor rotation. Need to re-do the wires if that's the case.
I wouldn't move the distributor if it ran good before. If you do set the timing once it's running again, you need to disconnect the vacuum lines to the distributor first and plug the ends of the lines. Then set timing and re-attach vacuum lines. The spec is around 6 degrees, but they run better if the base timing is set at about 10 degrees BTDC.


Sal

[highcking]

Really counter-clockwise? I was using a Suntune Card that said “C” which I took to be clockwise! I will check on this. Thanks for the reply!

[highcking]

Sal - many thanks, started right up, no thanks to Suntune. Bad news is that the replacement advance unit seems to be doing the same as the old unit. It retards the timing at idle but doesn’t advance it at higher rooms. Timing is sitting some number of degrees ATDC at idle. Suggestions?

[highcking]

That’s higher rpms, not rooms!

[dmsfrr]

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Originally Posted by highcking

... Timing is sitting some number of degrees ATDC at idle. Suggestions?

What is ATDC? After top dead center?

At idle with the distributor vacuum lines disconnected (and plugged) the timing pointer should be 6 to 10 degrees 'Before' TDC, on the advanced side of TDC.
Example photo #2: not a Fairlane pulley but the timing marks are laid out the same way.

Check & set the points before setting the timing. If they aren't correct the timing won't be either.
.014 to .016 inch point gap, or 26 to 28 degrees Dwell.
.

[scicala]

What dmsfrr said is 100% correct. Check and reset your base timing at idle like he said.
Also, you won't really be able to see the timing advance in neutral with a timing light since the advance is based on venturi vacuum (suction) and it won't be enough without the engine under a load to see a significant timing advance.
It sounds like your timing is retarded at idle currently. Make sure the points are correctly gapped first, since a different gap changes the timing slightly like dmsfrr said.


Sal

[highcking]

Many thanks for the replies. Let me be a little clearer. The timing is set at 6 degrees BTDC with vacuum lines to the Loadomatic plugged. When I reconnect the two vacuum lines, with the engine still at idle, the timing retards into the after top dead center region. Revving the engine does not move the timing mark. I see Sal's point that revving in neutral won't advance the timing. Is it the case that the Loadomatic retards the timing at idle to avoid "ping?" I've had this car many years and never really looked into this. If this is correct behavior, then my other Loadomatic unit was OK.

The problem I've been chasing is this. The car will accelerate to say 40 mph smoothly. Then, if you squeeze the accelerator slowly, the engine just sits there at the same rpms. If you pump the acclerator a few times, the engine will respond and the car will accelerate as it should. I've never had another vintage car do anything quite like that. It's the old "carburetion or ignition" issue.

[40 Deluxe]

No, the timing should NOT retard at idle with the lines connected. And, timing should advance when revving in neutral if both diaphragms are good. After all, both venturii and ported vacuum are present at a fast idle, say 15-1800. Have you checked the diaphragms for leaks? A good old-fashioned suction/tongue test is all that's needed. If you can get a good seal with a vacuum hose, just suck on the line and block with your tongue for a few seconds to see if it holds vacuum.

[highcking]

I have tried the "mouth suction" test on the NOS unit and it seems to respond properly. Even if it didn't, I can't see how the timing retards. Let me retest tomorrow to confirm the facts as I have stated them. I am pretty clear that revving the engine did NOT result in timing advance. This is apparently the result of the design --- there is no centrifugal advance, just that weird little valve mounted on the Holley 4000.

[KULTULZ]

Deleted

[highcking]

A few extra data points on my Loadomatic system. Timing results:

No vacuum lines connected: 6 degrees BTDC
All vac lines connected: retarded into ATDC range
Ported vacuum only: same, retarded into ATDC range
Manifold vacuum only: 6 degrees BTDC

The problem I am trying to solve is a strange form of poor performance. Engine starts instantly, never misses, backfires, etc. and idles smooth. Problems? Hesitates on sudden acceleration, though I can see the accel pump jets squirting. Weirder problem is that engine rpms do not come up with pressing down the accelerator pedal slowly. (Linkage is free and moves fine by hand.) You can get all the way to the floor and be going 35 mph. If you pump the pedal, you can get the car moving to higher speeds. Without pumping, you’re dying on a hill. With a 200 hp Y-block!

Holley 4000 is a Suter rebuild from a few years back. Electric choke works fine, choke plates open when warmed up. I have another rebuild I can slap on if need be. I just can’t figure how the engine can be turning low rpms (albeit smoothly) with the pedal almost to the floor.

Bill in Luray

[Stiggy]

Originally Posted by highcking

A few extra data points on my Loadomatic system. Timing results:

No vacuum lines connected: 6 degrees BTDC
All vac lines connected: retarded into ATDC range
Ported vacuum only: same, retarded into ATDC range
Manifold vacuum only: 6 degrees BTDC

The problem I am trying to solve is a strange form of poor performance. Engine starts instantly, never misses, backfires, etc. and idles smooth. Problems? Hesitates on sudden acceleration, though I can see the accel pump jets squirting. Weirder problem is that engine rpms do not come up with pressing down the accelerator pedal slowly. (Linkage is free and moves fine by hand.) You can get all the way to the floor and be going 35 mph. If you pump the pedal, you can get the car moving to higher speeds. Without pumping, you’re dying on a hill. With a 200 hp Y-block!

Holley 4000 is a Suter rebuild from a few years back. Electric choke works fine, choke plates open when warmed up. I have another rebuild I can slap on if need be. I just can’t figure how the engine can be turning low rpms (albeit smoothly) with the pedal almost to the floor.

Bill in Luray

Just wondering ~ has the problem been found with the spark retarding (with vacuum connected ) at idle??

[40 Deluxe]

Originally Posted by highcking

I have tried the "mouth suction" test on the NOS unit and it seems to respond properly. Even if it didn't, I can't see how the timing retards. Let me retest tomorrow to confirm the facts as I have stated them. I am pretty clear that revving the engine did NOT result in timing advance. This is apparently the result of the design --- there is no centrifugal advance, just that weird little valve mounted on the Holley 4000.

I found a chart showing the factory advance curve. It does not show any retard at idle. The advance begins about 500 RPM and shows 3 deg. at 1,000 RPM, 11 deg. at 1500, and 17 deg. at 2500. This would be steady RPM, not while it's revving up. So you can check it with a timing light.

[highcking]

Thanks! With everything connected, I see no advance at all. Someone commented in this thread that you won’t see any advance under no load conditions. There’s no centrifugal advance and the vacuum advance is related to lower vacuum conditions under load. It would be great if someone else could see what their car does under the timing light. I guess it’s possible I have two defective advance units.

[highcking]

I discovered with the help of my wife that the throttle linkage is slipping at partial throttle. On the linkage to the rear of the carb, there is a hefty pin that goes through a curved slot which I think is the downshift activator at full throttle. My linkage is slipping that pin at partial throttle which means the actual throttle on the carb stops moving entirely. It also explains why pumping works - the pin resets itself and allows more movement of the throttle. What the heck? I haven’t messed with that mechanism at all.

[scicala]

Attached is a link to a dual diaphragm schematic and text explaining the operation.
I don't understand how the timing is retarding at idle from the carb front vacuum line.
The only time it's supposed to retard the timing is on sudden acceleration just momentarily to avoid pinging (explained in the text). The inner diaphragm which is connected to the carb on the front of the carb only pulls in the advance direction.
The outer diaphragm which is connected to manifold vacuum is only for the momentary retarding of the spark on acceleration.


Sal


https://r.search.yahoo.com/_ylt=AwrJ...ZYEQ_dd0wsWrA-

[KULTULZ]

Originally Posted by scicala

The outer diaphragm which is connected to manifold vacuum is only for the momentary retarding of the spark on acceleration.

Sal

And de-acceleration.

The trouble here is that everyone has different ideas and theories of how the system is supposed to work.You ask questions to try and diagnose and there is no answer.

The system works on a modified (continually) manifold vacuum signal The 1956 DUAL DIAPHRAM was HOLLEY's last attempt to correct problems. DUAL ADVANCE was introduced the following model year.

Sounds like the OP found the problem in the accel linkage.

[highcking]

The only explanation I can come up with is that the spark control valve on the carb is not functioning correctly. It feels like the timing is just not advancing at all.

[Alaska Jim]

I was going to suggest that your problem sounds like a linkage problem, if when the throttle is pushed all the way to the floor and you can only get 35mph out of it. sounds like you found the problem, now to find the "cure".