Spec - rebuilt 57 type distributor (NAPA), single points, Edelbrock carb and B intake. Rump rump cam but not sure of specs. 312 .030 over. Top loader 4 speed. After a change in carb and intake, I noticed it was pinging (previously ran 3x2 with no vacuum to the distributor) so I checked timing. Took the vacuum line off the distributor (plugged). put on the timing light. Initial around 10-12 degrees. Put the vacuum line back on and checked for total. It went to about 50 degrees (tape on damper). Did not know rpm at that point. I thought total should be about 35 or so. Is this correct? Should the distributor be recurved to limit advance?



I guy told me that if there is no load, advance will be higher than if a load. Is this correct?



Thanks for any help

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Total advance is figured without the vacuum. Find out what RPM the at which the mechanical advance starts to advance. With the lopey cam, I think that the increase in RPM provided by the vacuum advance may be accelerating the engine enough so that the mechanical advance is starting to function. 40 degrees of vacuum advance sounds like a lot.


Lawrenceville, GA

Yes.

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Knowing the rpm at which the total advance is in would help as it is important in the grand scheme of things.   When performing a total advance reading, you essentially raise the rpms until the timing reading at the damper peaks out.  With stock distributor advance springs and with the vacuum advance line disconnected from the distributor and plugged, the engine will likely be over 4000 rpms before all the mechanical advance in the distrubutor is ‘in’ or taken up.  With the vacuum line disconnected, 36°-40° total is the value to shoot for.

With the vacuum line reconnected, the total timing will obviously be more once the engine rpms are brought up and 50° ignition timing is not to be unexpected as it’s now mechanical and vacuum advance working together.  If the distributor has been recurved by using lighter springs, then the amount of advance being supplemented by the vacuum should be reduced as it can now be too much advance at the lower rpms under a light load situation.  As I mentioned earlier, the rpms are a definite player.  And as Charlie mentions, without a load on the engine, the vacuum to the distributor will be intensified and thus give a higher no-load timing reading.  Under a load, the throttle blades are open more and because the port in the carburetor that supplies the vacuum to the distributor is further away from the throttle blades versus what the position is when simply reving the engine in neutral (no-load), the vacuum signal is diminished.  Engine vacuum as a whole is also reduced under a load and the ported vacuum signal also reduces along with this.  As the throttle blades continue to move away from this port, the vacuum signal eventually disappears thus allowing the engine to rely solely on the mechanical advance feature of the distributor.

Lorena, Texas (South of Waco)

Several of the "rebuilt" distributors from the various auto parts suppliers have been discussed on here - it seems that they are using the later advance fly weight system like this one....(I got photo from a site Charlie McCraney found).

Those familiar with this unit will see that the travel stop is in the "18L" slot - which is 36° crank degrees of total centrifugal advance. If you "power time" the engine as I usually do (raise the engine speed to full advance to set timing at 36°-38°) - when you let it return to idle, the initial will be way too low. if you do as the picture suggests (move to the "13L" slot) - the full centrifugal will be 26° - and the "power timing" procedure suggested above, will raise the resulting initial at idle to 10°-12°. This is all done with the vacuum disconnected - plugged at the carb. I like to change the springs too - so the advance curve is quicker - but that is another subject.

There are two types of advance pots around....this one with shims springs and a fiber tube stop.

And this one that adjusts with a 3/32 hex wrench.

They may be set to deliver as much as 25° advance at 15 inches Hg. If you are using a quicker mechanical advance curve in your distributor (as described above) - you have to turn them back to keep the engine from knocking at part throttle. Adjustment is basically trial and error - drive it/adjust it sort of thing. Hoosier suggested a good trick I use on mine - orfice the vacuum line to the dizzy so it doesn't change the pot position so fast - dampens things a bit.

 
 Steve Metzger       Tucson, Arizona

If you go to my topic of "wont idle in drive"I have a internet site listed on my last post which explains timing and advance very well.Do an internet search for "distributor timing and theory-part 1" should take  you to to an article in "hotrodder.com.If anyone can post a link to this article its good reading.

  

I could not find the article Mark was talking about but here is a good one. Mike

http://www.highperformancepontiac.com/tech/0212hpp_spark_plug_advance/index.html

1956 Fairlane Victoria (ORREO)

 

Overlooking Beautiful Rimrock AZ

Found it! Sure is a pain using different browsers to search and post. Mike

http://www.hotrodders.com/forum/distributor-tuning-theory-part-1-a-59033.html

1956 Fairlane Victoria (ORREO)

 

Overlooking Beautiful Rimrock AZ

Thanks to everyone - I will try this again w/o the vacuum line attached and look at the other mods and suggestions.



Paul

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ