Ok well today i went to advance auto parts and bought a new vacuum advance can to replace my adjustable can. The one the Advance sold me is VCD315 its what they had listed for a 75 vette. So i put it in and reset the timing. Im just wanting to know what is the stock can rated at on a 75 or do i need to take this back and go track down a ar-12.
My timing came out this
18 degrees at idle with the vac disconnected
36 degrees by 3000 again with the vac disconnected
38 degress at idle with the vac connected.

Does this sound right.


Yes i have read the sticky and every paper written about timing and tuning. Just wanting to run these numbers by you all.

Any input is appriciated.

Now for the carb i hooked the vacuum gauge up to see where it is and im at 12hg. The Car is running rich at idle. I have the idle mixture screws turned 1 turn out. The choke is open. The carb is a Holley 4160 Dual Feed Vacuum Secondary 750. Does it sound like i need a power valve? if so what one? from what i understand it would need a 5.5 pv. Thanks in advance.

 

Just got back from a drive. No pinging sounded great except for the exhaust leak from the cheap headers. To the carb. Its still runing a little rich and a idle you can smell it bad. There is no hesitation like there was its now a bog stumble. So im thinking its the richness of the carb. Which i think the power valve would take care of from what i have read. anyway thanks in advance for any help.

 

what is a VCD315? I have no specs on that can. at what vacuum level doews it come in at and how much advance does it supply as per the specs?
from your numbers anyway it looks like it's supplying 20º advance at idle but at what vacuum level does it start and be all in at?
you want to make sure that the vacuum can supplies the vacuum advance all in at least 2"hg BELOW the vacuum level that your motor is producing at idle so for example if your motor is producing 20"hg at idle as you state than you want the can to have the advance in by 17"hg or 18"hg.
Also, make sure the total timing WITH the can connected does not exceed 52º.

i'd also reconnect the vacuum gauge to your carb and make sure your idle mixture is correct, not just connect it to read the vacuum level. With the vacuum gauge connect to a full manifold vacuum source adjust your idle mixture screw(s) to achieve the highest steady vacuum reading. You may need to readjust the idle speed during this process to keep it at the correct level. Once you have the idle mixture set than reread what the motor vacuum is at idle and compare that to the specs on the can to make sure that the vacuum can you bought is bringing in all the advance at least 2"hg below the motor vacuum level

 

Its the vac can that they have for a 75. I guess its what GP Sorensen number is. They asked what type of car it was for and gave me that. I told them i need it a ar-12 and they just looked at me funny the same way the guy at napa did too. I will have to mess with the car some more this weekend too dark out now to mess with it.

 

as far as i could tell the vac can starts working as soon as i hook it up to the vac line. I have the vacuum line coming out of the vacuum port on the bottom of my carb so its full manifold.