When the gas formula changes in winter and summer, what are they doing to it, and how do we adjust our carbs to compensate? I just picked up a hesitation at takeoff, and started swapping rods thinking I needed to lean it out, but it got worse. Ended up making it as rich as I could with just a rod swap, and it runs much better now.
What grade gas do most of you put in 74 302? I tried 87 and it ran good, I put in some 93 the last tank and does not seem to be getting as good of mileage. I have not messed with any of the screws etc...
I run 87 "regular" since the 74 has low 8:1 compression. I have had a full tank for about 2 months, so a couple things may have happened... 1) Outside temps dropped into the low 70s in the last few weeks. Maybe running "summer" gas is making it hesitate. 2) Since the air is cooler, maybe it needs a different A/F ratio to burn efficiently, hence running better on richer rods. 3) New aluminum radiator, so car is running cooler. Whatever happened, I need to figure out what needle/jet settings to use for summer, and which to use for winter. I was wondering what most of you out there do to your carbs to make them work better when the seasons change. I know I need to adjust my choke when it cools off, and I have the choke marked for each season, I just need to document which needle and jet to use and approximately when to swap them. Eventually, I will learn that with the 1st strong cold front, I swap to X rods, and then after the first strong warm front, I swap to Y rods. I always leave the "screws" alone. Once I get the idle and idle mixture correct, I don't mess with them. Cool thing about Edelbrock Performer carb is between Wal-Mart (with trunk full of frozen chicken breasts and hamburger meat) and home, I swapped the rods 4 times, and the springs once, until I found the combo that stopped hesitating. Got home and the meat was still frozen...
I don't know what they do, but my car always seems to run better in the winter. That is, once you get it started!
"winter" gas has 10% alcohol mixed with it or another compound that leans the mixture out. Here in the Seattle area they just leave the alcohol in all year long. We can set our carbs up and forget it. If you live in an area that changes the gas for the season then you will have to richen your mixtures up about 5%. That is about two jet sizes on a Holley or Ford Autolite carb. I am not familiar enough with the other makes to say what change is required to make up the difference. I do know that if you leave the winter jets in during the summer you will get a bit more fuel consumption but with an increase in HP if you were running lean enough to feel the difference in the first place. My wife's car is a 72 and it had a lean surge at 55-60 when cruising. Drove me nuts until I remembered that my dad's 72 dodge wagon did the same thing and the dealer told him it was because the carb was an emission carb and they had to run lean to keep the air clean. Well, it ran great after I played with the jetting in the carb and nobody was the wiser for it. It still got 20 MPG on the highway and that's not too bad for a 318 in a 4200lb station wagon. If you have the original carb then just add a couple of sizes to the jet size and you will be happy with it. The "hole" or stutter or bog on take-off is a combination of the lean mixture and the accelerator pump return passage. There is a hole in the carb body that allows some of the accelerator pump shot to go back into the fuel bowl. More emissions crap! you can put a short set screw in it, use gasoline proof epoxy to fill it or a lead rivet. Take a piece of lead wire, 1/16" in diameter and cut it about 1/4" long. put it through the hole and peen it flat on both sides. Pt your carb back together and you will notice a big difference.
Thanks for the tech info, Paul. THAT explains why I ran better when I went with the richest rod I had. I think I might swap out to a richer jet and just run a little richer all the time. My plugs are always on the light side anyway...
