QuestionI have a 70 olds 455 with a rochester 2 barrel, runs great. I rekitted the carb, seems still to run a little rich. The jets were at 4 turns out on one, and 6.5 on the other, I set both to 4 turns out, no change. Is there anything with "nowadays" gas that would change the jet setting? Thanks
Answer4 turns out seems a bit far to me, I'd put a vacuum gauge on it and tune for maximum vacuum, with the car idling in neutral at about 600 RPM. If you cannot achieve 20 inches of vacuum, I'd start looking for a vacuum leak somewhere. (if you are at high altitude, you won't ever see 20 inches - I'm at 2000 feet, and I can get about 18 inches on a really well tuned engine (less air to compress, you know?) - so depending on where you live, the numbers might be different, but if you can only get 15 or so inches of vacuum, something ain't right!
As for the initial setting of the carburetor, I always start at 1 1/2 turns out, and then back each side out in 1/4 turn increments until I find the maximum vacuum - usually this is around 2 to 2 1/2 turns out. Keep the idle speed at around 600 RPM, while you adjust the screws - if it speeds up as you adjust it, you're going in the right direction, but keep correcting it back to 600 RPM with the idle speed adjustment or you will fool yourself as to the best setting. Also, keep the two sides the same distance out - if they want to be greatly different (more than 1/4 turn, and the tips of the adjuster screws are not messed up, there is still some crud in the carburetor. In an extreme case, when one side of the idle/low speed passage is completely blocked, the mixture adjustment on that side will make no difference at all (because no fuel is flowing in that side of the carburetor).
The modern gas causes a lot of problems, but mostly because it is much more prone to vapor lock, and because it attacks the older rubber items in the fuel system - so you should replace the fuel pump if it has not been replaced in the last 5 years or so, and also replace all of the rubber hoses in the fuel system, and don't forget the ones back at the tank! However, none of that will have any effect on the idle mixture (unless some crud from a deteriorating hose is blocking something in the carburetor). Also, with modern gas, in a high compression engine, you may get "ping" on regular gas - you would have to switch to premium gas, even on the 2 bbl engine, and perhaps even retard the timing a few degrees to avoid engine damage from pre-ignition (ping). Other than that, I don't think the modern gas is causing the car to run rich.
Dick
