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Classic/Antique Car Repair/Tuning Pontiac 400 engine


Hello, here is what I have. 1978 Pontiac Trans Am with a 400 engine bored.060 over, headers, alluminum intake, Magnum 270 hdy cam Quadrajet carb, 350TH transmission.Nothing radical just a simple upgrade above stock.

The problem I am having is trying to adjust the carb. Following all steps with a vacuum guage, setting curb idle all the regular stuff, but when i put it in gear it wants to stall sometimes and even goes dead. I basically have to drive it with two (2) feet.

I have had the carb kit built by a well known carb specialist known to Trans Am Country to all the specs I stated. Also have had the carb rebuilt by a very reputable shop here in MS. where i'm from.

I am so frustrated and don't know which way to turn. The season for riding is here and I am stuck,
Any suggestions

I checked the factory specs on this cam. Magnum claims that this is the most high performance cam that you can use with a stock torque converter. It also says that this cam in a small block will give a rough idle. This tells me that there is a lot of valve overlap between exhaust close and intake open. This gives the rough  idle and rough low speed. This tells me that you are chasing your tail trying to solve the problem via the carburetor. You might have to replace the torque converter with a high stall speed performance one or just live with a higher than normal idle.  

Classic/Antique Car Repair

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Brad Sears


All automotive including antique and collectible. However if the car has been modified I can only answer in general terms and maybe get you pointed in the right direction.


Automotive tech instructor. Syndicated auto columnist 1970's though the early 1990's. Syndicated auto radio talk show, Ask Brad About cars, CBS Radio 70's through 90's TV Show "Last Chance Garage" 1980's PBS-TV syndicated. Auto instructor for the following companies: Fram Autolyte Holly Carter AMF Ford Motor University Of Conn Blue Hills Technical School Sugar River Technical Center Grew up in a family garage in Needham Mass and turned wrenches from the age of 14.

Manchester Union Leader, Nashua Telegraph, Motor Service Magazine, Yankee Magazine, Popular Mechanics (Saturday Mechanic early 80's), Los Angeles Times, New York Times, and lots more.

More than I care to remember. Basically Franklin Technical Institute in Boston, Northeastern University, Fitchburg State Teachers College, Tufts University, and a lot of factory schools along the way.

Awards and Honors
Moto Award winner. And much more.

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