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**MikeB** · 04-26-2002, 08:48 PM

Your vacuum advance should make at least a 10 degree difference at idle, unless you are connected to a "ported" vacuum fitting on the carb. Another possibilty is your distributor has adjustable vacuum advance which is set too tight. Is there an allen screw in the vacuum line nipple on the advance canister? If so, play with it a little. With the vacuum line plugged, you need about 8-10 degrees mechanical advance at idle, and 30-35 degrees total at 2000-2500 rpm. You should have 40-45 degrees total (including vacuum advance) at your cruise rpm to get good fuel economy. You can check total advance with a "setback" timing liight or by using timing tape on your balancer. Unfortunately, your stock distributor probably has less total advance that doesn't "come in" as quickly. It's probably something like 25 degrees mechanical that doesn't fully come in until 3000 rpm. You can change this with a $10 weight and spring kit.

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MikeB
69 C-10 Fleetside, mild 383, Dart Iron Eagle 180cc heads, Crane Energizer 266 cam and 1.6 roller rockers, Edelbrock Performer manifold and 600cfm carb, HEI w/ MSD components, 1986 front spindles/disc brakes, Vintage Air in-dash.

04-26-2002, 08:48 PM	#4
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,665	Your vacuum advance should make at least a 10 degree difference at idle, unless you are connected to a "ported" vacuum fitting on the carb. Another possibilty is your distributor has adjustable vacuum advance which is set too tight. Is there an allen screw in the vacuum line nipple on the advance canister? If so, play with it a little. With the vacuum line plugged, you need about 8-10 degrees mechanical advance at idle, and 30-35 degrees total at 2000-2500 rpm. You should have 40-45 degrees total (including vacuum advance) at your cruise rpm to get good fuel economy. You can check total advance with a "setback" timing liight or by using timing tape on your balancer. Unfortunately, your stock distributor probably has less total advance that doesn't "come in" as quickly. It's probably something like 25 degrees mechanical that doesn't fully come in until 3000 rpm. You can change this with a $10 weight and spring kit. ------------------ MikeB 69 C-10 Fleetside, mild 383, Dart Iron Eagle 180cc heads, Crane Energizer 266 cam and 1.6 roller rockers, Edelbrock Performer manifold and 600cfm carb, HEI w/ MSD components, 1986 front spindles/disc brakes, Vintage Air in-dash. __________________ Mike 1969 C10 LWB -- owned for 36 years. 350/TH350, 3.08 posi, 1st Gen Vintage Air, recent AAW wiring harness, 5-lug conversion, 1985 spindles and brakes. 1982 C10 SWB -- converted from 250-six to roller cam 350, Vortec heads -- sold 1981 C10 Silverado LWB, 305, TH350C -- sold, but wish I still had it! 1969 C10 (not the current one) that I bought in the early 1980s. Paid $1200; sold for $1500 a few years later. Just a hint at the appreciation that was coming. Retired as a factory automation products salesman. Worked part-time over the years for an engine builder and a classic car repair shop. Member here for 24 years! This is the very first car/truck Internet forum I joined. I still used a dial-up modem back then!