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I am hoping someone can tell me what additional advance should be gained once the vacuum line is reconnected to the canister on the distributor, after having set the timing.

I have a 66 with a newly rebuilt 454. While trying to set the timing (HEI is from a small block I think) at 8 or 10 degrees, as soon as we hook the vacuum line back up, the RPM increases by 800. Also, the vacuum advance readings shoot up an additional 18 or so degrees. This doesn't seem normal (from experience) and I was wondering if my vacuum canister may be the culprit.

Any help would be appreciated. Thank you.

Ian

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As an edit, I have the vacuum line attached to the ported vacuum on my 750cfm holley as Pat suggested (Thanks Pat). Could it be that vacuum is sneaking past the throttle plates?

[This message has been edited by Ian (edited 06-14-99).]
 

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20 deg vacuum advance canisters are very common. It sounds like you have your's hooked to full time vacuum. You might try hooking to ported vacuum. Look for a vacuum port on the carb that is above the throttle plates. On a Holley look on the passenger side above the primary idle mixure screw. On an Edelbrock or Carter look on the passenger side of the front of the carb.
 

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Yeah, as Pat said no biggie to find 18 in the vaccum side. Don't sweat it unless you find your motor pinging or anything like that at cruise. Then your total adv + vaccum is too much. Time the car with no vaccum and again, as Pat said, find the ported vacuum on your carb.
 

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Running 18deg of total advance can actually be low, depending on circumstance. I recently replaced the tired old 307 in my Chevelle with a 9.5:1 remanufactured 350 (which I love!) with a 600cfm Holly 4B and LT1 manifold. The guys who dropped it in for me changed the weights and springs on the HEI distributor. At idle, with the vacuum connected, I'm at around 18 deg but at full RPM it's over 30!! and purrs like a kitten (more like roars like a lion) with not the slightest hint of a ping.
 

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They make adjustable vacuum cans to regulate the amount of advance.But remember vacuum advances reduce the advance under full throttle to stop detonation.I run 42 degrees of total advance on a 9.5 SB that is all in at 3000 rpm on regular gas with no ping.And thats on manifold vacuum not ported...FRED
 
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