Timing & Gas Milage

[Rich72C10]

So I popped into the "What kind of gas mileage do you get with your 67-72?" and after I posted what I was getting it went south from there. I feel a bit bad since it became about me and my timing. So I am starting a new thread, mostly to see what the out come is. Or I hope there is one ;-)

Summary:
Engine rebuilt to stock with a mild RV Cam, still a bit under 1k miles on the engine (say reaching 700 miles). I got 10 mpg this past Sunday for the 1st time with reasonable mixed driving. My timing is set to 12° but I found that my Vacuum Canister on my distributor leaks, takes it under 25 seconds to drop to 0 after pumping it to 15~20hg. I am trying to learn how to properly find both mechanical and vacuum timing - I am thinking I didn't do that right last night.

Currently I have what the previous own put in (he bought it from Ebay), a Top Street Performance JM6701. Not much you can do with it, other than set timing. The Vacuum Canister is a odd thing that will not take a replacement off the shelf, though they are sending me one for free. During the rebuild my bother and I did talk about replacing it - just to have a known brand.

I finally decided to buy from Summit this morning a PerTronix Ignitor III D7100700 with their matching coil. This unit looks very similar to the Top Street Performance distributor, its black, small-ish, and has female connections on the cap - which from a visual stand point what I am wanting. I know a lot of guys say go with a GM HEI, even go get one from a junk yard. But those things are monsters and I don't like the look of them. The deed is done and at least I should be able to support this one better than the TSP distributor.

I also have a 72 Quadrajet 4BBL at Quadajet Power but I don't expect it back until March. My installed Quadrajet is from a 78 Truck that the previous owner put on and while it was rebuilt, I am not sure how well it was jetted during the rebuild (there was a lot of questions around its rebuild when my brother & buddies had it apart a few times).

As I get stats from timing and MPG changes I'll try and keep this tread updated.

PS:
As for how the truck is running, outside of MPG, I have no complains. She takes off like a bandit, even spinning the tires if I dog it. At any speed I can give it WOT and she immediately goes. No hesitation or mis-firing that I can notice. I have had it in two different shops for various things (O'Ring replacements/Transmission leak fix) neither offered up "hey, you have timing problems". They actually both said in one way or there other, she is a nice truck and drives great.

PSS:

• SBC 350 Rebuilt less than 1k on engine at this posting.
• TH350 Rebuilt at same time as engine.
• 307 Gears
• Power Brakes and A/C (off during all timing checks)
• 12° Initial timing
• 30° ~3500 Max Mechanical (by offsetting light ° button to read 0 on the timing mark)
• 45° ~3500 Max Vacuum (by offsetting light to read 0 on the timing mark)
• 17 hg Vacuum @idle
• Park/Neutral Idle 650
• Tires 275 60 15
• 60 MPH = ~2500 RPMs

Update for Real World MPG with my rebuilt 72 Carb from Cliff and Progression Ignition:
March 25th 2022, 14mpg on a 275 mile trip on Texas Hwys from Kyle to Kilgore Texas. This is mix driving were a lot (most) is 65~75 state Hwys and little towns on the way.