Classic/Antique Car Repair: carberator, pollution control laws, vacuum hoses

Question
Brad,
I have a Ford F-150 6 cylinder 300 cu. in., I think the motor is an 83, I  have had the pollution control equipment removed.The carburetor I have on now gives me very very poor mileage, can you recommend an earlier carburetor or an alternative to solve my problem? I live in Idaho where we have no pollution control laws.    

Thanks,

Tony Myers

Answer
There is more to this question than taking a carburetor off the shelf to improve fuel economy. The problem could be miss routed vacuum hoses when the pollution equipment was removed. The most common thing that I have found when diagnosing these modified vehicles is that the vacuum feed to the vacuum advance on the distributor has been miss routed. If there is no vacuum to the distributor under cruise conditions the fuel economy will fall off sharply. Next is the vacuum routing to the air cleaner. The air cleaner when the car was built had a trap door in it that pulled warm air from the exhaust manifold to help the engine warm up. When the engine reached operating temperature the trap door is supposed to open and allow cooler air from the schnorkel of the air cleaner to be drawn into the engine. The trap door stays in the "pull the air from around the exhaust manifold" when there is no vacuum to it. If this is the case fuel economy will also drop off especially in warm weather. These are the first things that I would check before deciding on a replacement carburetor. Keep me posted as you go along please.