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**MikeB** · 10-08-2015, 08:47 AM

I don't think 72 trucks used electric choke Q-jets (I know a 69 didn't). If that's true, some previous owner probably installed a later model carb and wired the choke to a 12 volt ignition "on" source. Maybe the wire came loose or a fuse is blown. BTW, I assume you know that 12 volts causes the choke to slowly OPEN, as the current heats up a bi-metal spring.

The rear butterflies on the top won't open until air "demand" by the engine is high enough, like when you are accelerating with your foot to the floor. But just revving the engine in Park or Neutral probably won't open them. If they are connected to the choke linkage, that's probably to make sure they don't open when the choke is on.

10-08-2015, 08:47 AM	#3
MikeB Senior Member Join Date: Jul 2000 Location: North Texas Posts: 3,663	Re: Confused by carbs... I don't think 72 trucks used electric choke Q-jets (I know a 69 didn't). If that's true, some previous owner probably installed a later model carb and wired the choke to a 12 volt ignition "on" source. Maybe the wire came loose or a fuse is blown. BTW, I assume you know that 12 volts causes the choke to slowly OPEN, as the current heats up a bi-metal spring. The rear butterflies on the top won't open until air "demand" by the engine is high enough, like when you are accelerating with your foot to the floor. But just revving the engine in Park or Neutral probably won't open them. If they are connected to the choke linkage, that's probably to make sure they don't open when the choke is on. __________________ 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! Last edited by MikeB; 10-08-2015 at 08:54 AM.