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**WorkinLonghorn** · 03-06-2019, 05:51 AM

SavageC20, you need to hook up that vacuum advance. You are running around with a severely retarded ignition at part throttle loads. This WILL cause extra heat. If you didn't notice a difference with it hooked up, then maybe the diaphragm is broken or the vacuum source is plugged or the wrong one.
Take a hose and hook it up to the distributor vacuum advance port ( the one on the distrib.)and test it to see if it holds vacuum. Just use your mouth. Take off the cap and see if there is movement when vacuum is applied. Then hook up the hose to the correct vacuum port on the carb (metered vacuum = no vacuum at idle, some vacuum at part throttle only) to see if you get vacuum there at part throttle.

Sometime you don't notice a difference but believe me, you need vacuum advance.

This is really a "no brainer" and I am surprised that no one is seeing this.

Did you know that the stock vacuum advance for a 396 adds 15° advance at part throttle only?

03-06-2019, 05:51 AM	#22
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,861	Re: How hot do Big Blocks normally run? SavageC20, you need to hook up that vacuum advance. You are running around with a severely retarded ignition at part throttle loads. This WILL cause extra heat. If you didn't notice a difference with it hooked up, then maybe the diaphragm is broken or the vacuum source is plugged or the wrong one. Take a hose and hook it up to the distributor vacuum advance port ( the one on the distrib.)and test it to see if it holds vacuum. Just use your mouth. Take off the cap and see if there is movement when vacuum is applied. Then hook up the hose to the correct vacuum port on the carb (metered vacuum = no vacuum at idle, some vacuum at part throttle only) to see if you get vacuum there at part throttle. Sometime you don't notice a difference but believe me, you need vacuum advance. This is really a "no brainer" and I am surprised that no one is seeing this. Did you know that the stock vacuum advance for a 396 adds 15° advance at part throttle only? __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent. Last edited by WorkinLonghorn; 03-06-2019 at 06:05 AM.