i've got a buick 350 with a 2bl carb and i believe the fuel mixture is too rich.I am wondering if there is a proper or standard amounts of turns on the mixture screw on the carb to apply so i can compare my settings?
First of all, let me point out that adjusting the mixture screws only affects idle mixture and has no affect on the mixture when driving. Anyway, the proper procedure is to first set the timing and idle speed to the proper specs. Then hook up a tach if you don't have one and adjust the mixture screws to obtain the highest RPM. Then readjust the idle speed to 50RPM higher than desired speed. Then turn each mixture screw in slightly to reduce RPM by 25 for each screw. This gives you the correct idle speed and mixture.
idle mixture/ run mixture Basic setting; :Smarty: GENTLY run the idle mixture screws all the way in to bottom them out. Then back up 1 1/2 turns. Basic setting. :Smarty: Then after the engine has warmed up 20 min. Slowly turn each screw in untill the engine begins to run rough and lose rpm and then back up untill it runs smoothe again. Then if you want the fine adjustment, hook up a vacume guage to intake manifold vacume and adjust to the highest vacume reading. That is for the idle circuit. It doesnt affect the running rich at speed. There are many things that affect richness at speed. some of these are; :Smarty: Choke set too tight. Dirty air cleaner element. Carb float level. Needing a good electrical tune up. all of the above. The choke should be set on a cold engine, before it is started. Set to where a 3/16 drill will fit between the lower edge of the choke plate and the main body of the carb. COLD. :Brow: One of the biggest secrets of making a carb perform is to set to the exact factory specs. You can work on the carb from now on and it wont improve if your engine needs an electrical tune up. :Smarty: so start on the electoronics first. every body wants to dive into the carb but 90 % of the time the problem is electrical. If the car has the old point system, get rid of them. Install one of the modern pointless ign. systems. The factorys got rid of them for a reason. :laugh:
I agree that checking the electronics is the best place to start. I worked for an old-timer at a speed shop for a shile and he said that more than 90% of the cars that came in 'needing carb work' really needed ingnition tuning often including distributer repairs. One mistake that can raise havoc on carb tuning is to open the butterflies too much with the idle set screw then needing to back the idle enrichment scwers out too far to compensate. If you are infact running too rich, I would start by checking for a stuck/sunk float or poor needle/seat seal. Using an electric fuel pump can often push fuel past the needle also. Good luck.
