G14 runs too rich

[oldjohnt]

I have a G14 with rebuilt engine, new carb, starts instantly, idles smooth even and sweet and runs great. HOWEVER if riding on the rear seat the exhaust smells over rich (but no black smoke) plus the spark plug (Autolite 66 or NGK or Denso makes no difference) is always flat black sooty coated NEVER the nice warm gray color.

I assume the power jet is fixed but it has some sort of an idle adjustment screw (NOT talking about the dead idle stop) but Im unsure how to adjust it for a leaner operation. If it were like a power jet screwing it in would lean the mixture, but if some sort of an "air bleed" screwing in may reduce air and make it richer.

QUESTION how do I adjust the idle screw and how can I make it run leaner??????????

Old John T in Indiana

[golfcartg]

You typically want to start by focusing on the air/fuel mixture screw. This is where you control how much air gets mixed with the fuel. If it's an "air bleed" type screw, turning it in will reduce airflow and make the mixture richer, turning it out allows more air, leaning out the mixture. On most golf carts, adjusting the mixture screw for a leaner operation involves turning it out slightly to let in more air, but it's important to make small adjustments and test as you go.

You mentioned you replaced the carburetor, one thing to keep in mind especially when dealing with replacement carburetors is that they often come preset from the manufacturer and unfortunately, they’re not always dialed in for your specific setup. Many aftermarket replacement carburetors aren’t built with the same precision as the original OEM units, and the tolerances in the jets and air/fuel passages can be off. Sometimes, they don’t even allow for fine adjustments, leaving you stuck with a mixture that’s too rich or too lean. The main jet or power jet may be drilled to sizes that don’t perfectly match what the engine needs resulting in performance issues and that overly rich exhaust smell you're noticing.

In your case, even though the carb is new, it’s worth questioning whether the idle adjustment screw on the aftermarket unit is giving you enough control over the air/fuel ratio. Some aftermarket carbs come with fixed jets that make it impossible to fully adjust for local conditions, load, or altitude. OEM carburetors, on the other hand, are built to much higher standards allowing for finer tuning and more reliable operation over time.

Looking at the attached chart. The spark plug color is one of the best ways to confirm what’s going on. If you're seeing that flat black, sooty coating after a ride, it means the mixture is too rich, possibly due to the limitations of the aftermarket carb. A well tuned system should give you a light tan or gray plug color after a good run which indicates optimal combustion. But no matter how well you tune it, keep in mind that the exhaust on these carts will always have a strong smell, as they don’t have catalytic converters. The exhaust doesn’t get hot enough to support one, so all the unfiltered fuel vapors are just coming straight out, and without the filtration you'd find in modern vehicles, that smell is unavoidable.