Trouble idling.

Hey guys. I have a SBC 350, and 350 Auto trans. Holley carb #3310 (4160) carb. The car idles fine in park but falls on it's face when put in drive. The cam card is attached. I have checked for vaccum leakes and have adjusted the float level. I am stumped. When I set the the idle speed in park I am at about 1300 rpms then I put it in drive and it goes to 600-700 rpms or die. I do not know what else to check. I have played with the mixture screws and my timing is set at 12 BTDC. What am I overlooking? Thanks in advance.

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Originally Posted by huero

The car idles fine in park but falls on it's face when put in drive. Thanks in advance.

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Hi Huero and welcome to the board.

My guess is that your carb has a problem. Maybe you can adjust it or just maybe you need to rebuild it or buy a new one. First off, set your ignition timing at the said 12 degrees with the vacuum disconnected at the distributor. Then slow the idle to 900 in park. Then try and richen the mixture by turning the idle screws counter clockwise until the rpm drops 100 rpm.

The thing that happens with a bigger cam is that there is less vacuum which means less air flow at idle which translates into a bad fuel/air ratio being drawn into the combustion chambers. What everyone does at this point is turn the idle screws in to speed up the idle to try and compensate.
However this in turn opens the venturies and allows even more air rather than a correct mixture. The trick is to allow more air flow without opening the butterflies. You can achieve this with a four corner idle screw carb and adjusting accordingly or else by drilling two small holes in the front two butterflies. Sometimes a larger flowing pcv can help if you have a breather on the other valve cover.

Thanks Typhoon. That I have yet to try. I will give it another shot over the weekend. Right now I am giving it a rest. :mad: The carb is brand new.

Was this resolved?......Not sure on what camshaft you are running, if its a fairly big grind, you may need a looser torque convertor (higher stall).