My first post is very near and dear to me. It addresses the issue of a carbureted vehicle “running rich”, “over-fueling”, idling the engine makes your eyes water, etc. Over the years, this question has been posed to me countless times. If I had a nickel for every time…….you know the rest. I can promise you that one of these suggestions will help your vehicle run normally when checked properly. Please take the time to read every suggestion carefully, and be honest with yourself about a setting or adjustment; don’t just assume that the fuel pump is making the “right amount of pressure” because the box that it came in says so! Check, and double check, you have nothing to lose, and everything to gain by surgically eliminating one possible issue at a time.
First, check for too much fuel pressure. Many original style mechanical pumps run at 7psi fuel pressure or higher. Aftermarket pumps also run high fuel pressure. Edelbrock carbs, Rochester 2 barrels, 4-jets, and Carter AFB’s do not need anything more than 5-6psi! Holleys, Demons, and Q-Jets can run okay with 8psi, but your street car doesn’t need it, and only a serious 600HP+ combo needs that much pressure, and even then, volume is king. Check and make sure your fuel pressure is below 6.5 psi as it says in the instructions of any of those carbs I named. If it isn’t, you need a fuel pressure regulator such as an Edelbrock, Holley, Aeromotive, or Mallory unit; all great quality & reliable units (stay away from auto parts store chrome chinese regulators, sorry Spectre & Mr. Gasket). If you fix the fuel pressure and the motor continues to run rich, the needles & seats should be replaced since they may have been compromised because of the high initial fuel pressure.
A few other things contribute to a rich condition:
1) Too much fuel pressure (needs to be below 6.5psi or under manufacturer’s requirements)
2) Improper float level (need to check your specific carburetor requirements)
3) Needles are stuck open in the seats because of debris or wear; must replace.
4) The floats are sunk; small hole in the float allowing fuel to go inside.
5) The metering has not been changed for higher than sea level altitudes. All carbs, unless explicitly stated, are calibrated at sea level. Even a minor 1500-2000 ft. elevation change will affect overall metering. Carb gets richer the higher you go.
6) Low manifold vacuum, under 10” hg, causing the metering rods or power valve to signal, dumping fuel into the motor. Use correct springs/power valve for cam duration/manifold vacuum reading.
All of these suggestions are based on a healthy, normally operating engine. If your engine has a dead cylinder, vacuum leak, oil consumption problem, or something else that is causing erratic running, none of this will help you. You will need to fix that major problem first, before attempting to blame the carburetor for the rich condition. Until next time…
