I have zero advance when checked under timing light throughout the rpm range. I suspect i need a new vac advance unit for the distributor. I bought what was advertised as a NOS B5S 12370A on Ebay. The unit came in the correct box but was considerably greater in diameter than what I took off the car. With the replacement unit installed, it pulled way too much advance, so i suspect that this is the wrong vac unit. I have called and checked around and have not found another source for the unit. Anyone know a source? BTW, i am trying to cure a stumble that kicks in just when i open the throttle off idle. I figure i cannot even attack that issue until i ensure that the timing is correct.

Jim

Jim H

BTW, the diameter of the old (presumably correct) vac advance was 3" and the diamter of the replacement wich is pulling too much vacuum is 3.75"  Can anyone verify diamter of the correct VA for a 55 T-Bird so i will know i have the right one?

thanks,

Jim

Jim H

Jim

It will really help if you can describe your engine in more detail. What carb do you have? A Holley 4000 or a later replacement carb?

You obviously have a 1955 distributor ( with tach drive) right? Since I replaced my 55 distributor with a 57 and the 55 distributor is deep in the garage I can not help with the size of the vacuum advance can but I do remember it was much bigger than the 57.

Can you tell us how the vacuum lines are hooked up to the carb? Here is a description of the Load O Matic I copied from the web that may help "that distributor is a load-o-matic, it uses only a very sensitive vac advance, it gets a controlled vac supply, from a spark control valve on the carb, when your at low speed, a " door " is opened part way under load ( not just revving ), depending on throttle position, this allows advance to occour, you might see 15 HG at the dizzy, once you start moving faster, and vac goes away, air is forced passed this door, through a controlled venturi, and that creates a controlled vac, sent to the distributor. this advance system matches ignition advance timing to the load required"

There are real experts on the LOM distributor on this site and you will get answers Pete

Jim,



Diameter of B5S-12370-A is 3 1/2". If you are getting way too much advance from any Loadomatic-type diaphragm that is hooked up correctly (to a properly functioning teapot spark control vacuum port), it is more likely your advance springs need to be adjusted/replaced. Find someone knowledgeable with a Sun machine, or if it is long overdue, send the distributor to Jim Weatherly for a rebuild. As for the carb, if a proper idle adjustment (accelerator pump working?) doesn't help, and it is also overdue for rebuild, send it to Pony.

Expensive, yes. But, the improved performance of rebuilding both (if needed) may make you think someone installed a supercharger when you weren't looking!

6 VOLTS/POS. GRD. NW INDIANA

Thanks for replying, Pete and Daniel. The carb on the car is the (presumably correct) Holley Teapot and the VA line from carb to VA unit runs just like you see in all shop drawings. Before I get into rebuilding the disty or carb, I would like to get a handle on what is wrong. Clearly the larger VA unit I installed is pulling too much. Believe it or not, I loosened the vac line where it goes into the VA unit to create a "controlled" vacuum leak, and this loosening brought the advance down into spec. That's why i tink locating the correct VA unit and setting the timing correctly will help in this diagonistic project. Any suggestion on where to find one would be appreciated - all the usual suppliers say "call for availability" and no luck.

While on the subject of spec, i have another timing question. The shop manual says initial advance is 6 degrees (automatic car) and total advance at WOT should be 31 degrees.  Both of these degree figures are listed in the Ford shop manual as being crankshaft degrees (not distributor degrees, which I understand are ½ of crankshaft degrees). Is this correct and does it mean that on my digital timing gun I should be looking for 3 degrees initial advance and 15 degrees total advance?? That doesn’t sound right to me.

 Jim

Jim H

If your timing light is reading off a plug wire  - it is reading crank degrees. The distributor is turning at 1/2 crank speed so 6° at the crank would be 3° at the distributor.

 
 Steve Metzger       Tucson, Arizona

[quote][b]wjhpc (1/1/2012) Any suggestion on where to find one would be appreciated - all the usual suppliers say "call for availability" and no luck.



Tom Sestak has a NOS unit. Pricey, but he stands behind his stuff, and it won't be chinese repro junk. Go to his eBay store.



P.S. Have you looked under the distributor cap to make sure both advance springs are present/unbroken?

6 VOLTS/POS. GRD. NW INDIANA

RESOLUTION: put the correct sized VA unit on and timing is now set at factory specs and pulls 29 total advance. Now back to my initial quest to eliminate the stumble on first opening throttle!

Thanks to all.

Jim

Jim H