Dorton also cautions that there are a few ways that a poorly adjusted carburetor can cause your car to be slow through the turns--particularly a turn exit. Fuel sloshing in the carburetor can cause the engine to stumble or bog a bit when the driver picks up the throttle, especially on high-grip tracks where there is strong side-loading.
Good communication follows...
Good communication follows beyond just talking to the driver while he or she is sitting in the car, a discussion of all the notes taken during practice is essential to creating a winning formula.
You may also want to keep an eye on your float levels if you notice a stumble or hesitation through the turns. If you have the float level too low, high-g turns can sometimes cause the left-side secondaries to become uncovered. This is especially true on the rear of the carburetor where fuel can not only be pushed to the right side of the float bowl, but also the rear as the driver accelerates out of the turn. In situations like this, you may have to raise the float level a bit.
On the front of the carburetor, you may also have to deal with spillover if you're able to get the forward bite maximized for very hard accelerations. If the float level in the front is too high, the fuel can actually spill over into the vent tubes. This time around you may need to lower the float level.
Often, it can be hard to determine exactly what carburetor adjustments need to be made. And since practice time is limited, you don't have time to be making a bunch of different changes. When you're trying to determine the best change to make, Dorton suggests going ahead and making your changes in big steps. This way your driver should be able to tell you exactly what the change did to the car's performance. Either it helped performance or it hurt it. You may have to go back and tone down the adjustment a bit, but at least you won't be wasting time with tuning changes that are too small to really let you know which way you need to go.
After practice is complete, Dorton recommends performing another visual inspection. Again, you're checking the belts for wear, oil and coolant leaks, burned plug wires, and anything else that might be amiss. Dorton also makes it a habit to talk to the driver just to get his opinion on the state of the engine. Ask him or her how the engine responded to throttle inputs, if everything sounded OK, and if he noticed any vibrations. He or she should also be able to tell you how hot the oil and water temps got during the run.
"The absolute last thing I want to do between practice and the start of the race," Dorton adds, "is have to change the plugs. You want to avoid installing any new plugs at all costs right before a race, because you just don't know if you are going to get a bad plug. You won't discover it until the race starts, and then it's too late. I encourage teams to keep a set of plugs on hand that they ran some laps on during a test session. That way, you know they're all good."
Granted, these guys are not tuning on the engine or carb, but having multiple team members is a major help in getting numerous tasks done simultaneously as you can see Ross Kenseth’s crew doing here.
If you get water or oil temps that are higher than usual, and the cooling system seems to be in working order, you should check to make sure the engine isn't going lean. Often, this isn't a jetting problem, but a problem with fuel delivery instead. Check that the fuel filter isn't clogged, there are no leaks in the fuel lines, the fuel pump is working properly, and the pickup in the fuel cell hasn't moved.
A quick visual inspection of the tailpipes is also a good way to get an idea of how the engine is running. Dorton says he usually carries a flashlight to help him see inside the tailpipes as far as possible, but as long as you can see approximately 12 inches up the exit of the pipe you should be fine. If all is well, the inside of the pipe should be light chocolate color. The color is from the carbon deposits from the exhaust. If it's white or ashy, that's a sign the engine is running too lean. If it's dark or excessively sooty, then you're probably running too rich. Sooty pipes can also signal a blown power valve. If they're oily, that's a sign you may have a ring sealing problem.
The tailpipes are a good indicator...
The tailpipes are a good indicator of how the engine is running. Dorton says they should be a light chocolate color approximately 12 inches inside the pipe. Too light means a likely lean condition, while too dark can mean a blown power valve or a carburetor that’s running too rich.
One area that often leaves many engine tuners barking up the wrong tree is trying to read plugs at a short track. Dorton says that there is simply too much idling and off throttle driving that it contaminates the porcelain on the plug and makes an accurate read too difficult. "Plus," he adds, "to get a good read, you need to do a clean shut off, where the driver kills the engine while at full throttle. But most Saturday night short tracks aren't set up for green-flag pit stops like you're used to seeing in NASCAR's Sprint Cup Series. The entrance to pit road is often tight with very sharp curves, and cars can't coast all the way to the pits. It's just too dangerous to ask a driver to do a clean shut off at most short tracks."
What you can do, however, is keep an eye on how much heat the plug is seeing. The farther the heat ring travels up the plug, the more heat your engine is seeing. This is something that changes from engine to engine, so you'll have to get an idea how heat discolors the plugs on your engine. But, for example, if you pull a couple plugs after practice and notice that the heat ring extends all the way up the threads of the plug, it's a sign that your engine may be running too lean.
Use these tips as guidelines to ensure that your engine is in top shape when you get to the track. Remember to always be thorough in your inspections and keep detailed notes.