Dual Point Distributor Vacuum Advance Spring

[challboy728]

The previous owner of my T/A brazed the distributor vacuum advance arm in place (Pictures attached). I replaced the vacuum advance unit with a similar unit. We dyno'ed the engine after rebuild, the tech at the dyno shop thought there should be a spring in the vacuum advance unit. Checked the shop service manual, and they don't have any service procedures for that specific distributor and vacuum advance. Should there be a spring in it? If so, what wire diameter, outside diameter and length?

I put my best guess at a spring in it. After the car warms up, the engine wants to die when the transmission is in gear. Could this be related to the vacuum advance?

Thanks for any help you can provide!

 

[moparleo]

Is the engine rebuilt to factory specs ? Should stay running at idle with no advance input if setup is stock and engine is stock, any changes to cam etc.. changes everything.

 

[challboy728]

The engine is stock.

 

[challboy728]

I did put a Petronix electronic ignition conversion in it, however.

 

[toolmanmike]

@halifaxhop

 

[halifaxhop]

That style of vacuum advance has a spring and some shims to dial it in. If it was braised the rubber is probably junk now and not worth the effort to re use it. I probably nave a rebuilt one and can figure out the spring rate if I have all the info. Not cheap though prob 110, but will be oem not a repop.

 

[Chryco Psycho]

I bet the stalling has nothing to do with the vacuum advance . if the dist is affecting it it could be the mechanical advance where the advance is increasing [adding advance] until you put it into gear then as the rpm drops when you put it into gear the advance drops down , meaning the springs are too light , the advance should be stable until 1000 rpm approx .
The other point is as you put it into gear the vacuum drops in the intake so it is more likely that the powervalve or metering rods are opening up meaning you need lighter powervalve or springs so they remain closed as the vacuum drops .

 

[challboy728]

That style of vacuum advance has a spring and some shims to dial it in. If it was braised the rubber is probably junk now and not worth the effort to re use it. I probably nave a rebuilt one and can figure out the spring rate if I have all the info. Not cheap though prob 110, but will be oem not a repop.

I replaced the vacuum advance with an oem unit. It did not include the spring, unfortunately. I put my best guess for a spring in it. I would be curious to know what the spring rate should actually be.

Thank you for your response!!

 

[challboy728]

I bet the stalling has nothing to do with the vacuum advance . if the dist is affecting it it could be the mechanical advance where the advance is increasing [adding advance] until you put it into gear then as the rpm drops when you put it into gear the advance drops down , meaning the springs are too light , the advance should be stable until 1000 rpm approx .
The other point is as you put it into gear the vacuum drops in the intake so it is more likely that the powervalve or metering rods are opening up meaning you need lighter powervalve or springs so they remain closed as the vacuum drops .

When I put the car in gear, the engine really pulls down, drops about 500 RPM. Also, when I start the car cold, the engine runs about 2000 RPM, drops down some after it warms up. I kinda suspect vacuum leak, but I haven't taken the time to check it yet.

I had the carburetors rebuilt by VintageMusclecarParts, everything was put back stock.

Thank you for the response!

 

[halifaxhop]

Your F

I replaced the vacuum advance with an oem unit. It did not include the spring, unfortunately. I put my best guess for a spring in it. I would be curious to know what the spring rate should actually be.

Thank you for your response!!

 

[halifaxhop]

FSM has where it should be at at certain points no real guide except part numbers and that is a guess since there are no specs on the numbers.

 

[Edward Hackett]

The previous owner of my T/A brazed the distributor vacuum advance arm in place (Pictures attached). I replaced the vacuum advance unit with a similar unit. We dyno'ed the engine after rebuild, the tech at the dyno shop thought there should be a spring in the vacuum advance unit. Checked the shop service manual, and they don't have any service procedures for that specific distributor and vacuum advance. Should there be a spring in it? If so, what wire diameter, outside diameter and length?

I put my best guess at a spring in it. After the car warms up, the engine wants to die when the transmission is in gear. Could this be related to the vacuum advance?

Thanks for any help you can provide!

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Make sure that Holley center carb choke is set properly. They really can't bench set it without it running on the engine. When the engine is cold, at fast idle, there is a spec on what the choke plate gap should be. Once warmed up, if you blip the throttle, the choke should snap wide open.
It's been years now, but if my memory serves me, there is an allen adjustment screw down in the vacuum diaphram in the vacuum advance pot. This what tensions the vacuum diaphram.
Anyone else have this memory?

 

[Chryco Psycho]

Yes there is an allen screw inside the vacuum advance on most Chrysler distributors that were not cast iron body , the screw limits the distance the diaphragm can move / total amount of degrees the vacuum can change the timing .

 

[halifaxhop]

There is a lot of confusion on that adjustment it does not adjust the amount of advance it adjusts the rate of advance. The only thing that can change that is the part that goes in and out of the vacuum chamber by grinding or wrapping wire around it.

 

[Chryco Psycho]

Well then try it , turn the screw counterclockwise all the way out until you here it click now apply vacuum to the canister & see if it moves . trust me it will not

 

[halifaxhop]

I do it every day we beat the hell out of this on FABO.

 

[Chryco Psycho]

I do it too all of the time , it locks out the advance on every one I have done it to , with the screw backed out all the way the diaphragm will not move outward as the screw hits the housing inside preventing the diaphragm from moving .
I guess the ones I work on are different .

 

[halifaxhop]

No I get the locking out because it locks the rate so high it stays. Was just saying that it adjusts the rate will not add more advance than what the arm is stamped. There is just a lot of confusion on it a lot of people thinks it adds or lessens the amount of advance it justsadjusts how much vacuum is needed to say start the advance.

 

[Chryco Psycho]

I would make a video , but i don't have a dist here

 

[halifaxhop]

This should help you can see when the screw is all the way out CCW, it compresses the spring I the vac advance, usually takes over 20 INHG to move the diaphragm when it is out all the way. when in CW they usually start moving at around 5 INHG, hope it helps explain it.