Newbie with CO Question

[Thrlls]

I have been reading Peter Z's book "The Used 911 Story" and on page 102 it talks about replacing the fuel lines that connect the pressure regulator and pressure damper. It goes on to say after these are changed you need to check the CO.
What is the CO? Carbon Monoxide?
And what kind of tool is it

Thank you!
Woody

[equality72521]

Carbon Monoxide, and a lot of people use a Gunson gas tester to set it.

[Thrlls]

Originally Posted by equality72521

Carbon Monoxide, and a lot of people use a Gunson gas tester to set it.

Thank you for your quick reply, you answered before I could edit!

So what is the proper CO level/measurement?
And how is it measured, or must this be done by a shop only?

[Thrlls]

Sorry, I believe I found the answer to my own questions.
In case anyone else was wondering.

AEP's Guide to Precision Tuning

Tuning your engine for better performance can be a time consuming and tedious job, especially when the tools required to gather engine operating data are unavailable. While for the enthusiast commercial tune-ups can leave much to be desired with respect to performance because the engine is typically tuned to factory specs rather than performance specs.

For years plug reading was recommended by automotive author’s as the way to ‘read’ the engine, but plug reading only gives a ball park feeling that is inferior to actual measurement. Gastester is the rational alternative to plug reading because it accurately measures the level of carbon monoxide in exhaust gas, and carbon monoxide is the principle indicator of fuel mixture. Why is it important to know the fuel mixture? Variations in the fuel mixture affect power output, fuel consumption and pollutant levels, so the ability to measure the fuel mixture is critical for successful engine tuning. Gastester is indispensable when replacing or tweaking the existing carburetor, when replacing the carburetor with aftermarket fuel injection, or when preparing for a state mandated emissions test.

Too often carbureted engines are set by ear and run richer than necessary to ensure drivability and performance under all operating conditions. However, a fuel mixture richer than necessary wastes fuel and spews excessive pollutants. The ability to accurately measure fuel mixture lets you tune so that maximum power is maintained while reducing fuel consumption and pollutants.

Auto Expert Products Co. And Gastester make precision tuning information possible and easy. AEP includes with every Gastester a power curve and a fuel mixture/percent carbon monoxide equivalence chart. The power curve runs from rich to lean and shows typical fuel mixture values for maximum power, low emissions, and balanced performance. The fuel mixture chart equates Gastester’s percent carbon monoxide readout to a more performance oriented fuel mixture value. Simply pick a performance level on the power curve and note the fuel mixture value. Then adjust the fuel mixture screw until Gastester’s readout displays the percent carbon monoxide that is equivalent to the fuel mixture selected. For example, a 12.6:1 fuel mixture provides maximum power equating to a Gastester readout of 5.0 percent carbon monoxide.

Figure 1.

The exhaust gases from a well tuned and mechanically sound engine are made up of relatively harmless nitrogen, water vapor and carbon dioxide. The actual pollutants, hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) amount to only around 2% of the total.

These pollutant levels are related to the air fuel mixture strength, especially CO emissions which are very low with weak mixture levels but rise steadily as fuel content increases. HC and NOx levels are also dependent upon ignition timing, with the hydrocarbon content showing an increase with both advanced and retarded ignition, whereas the NOx levels rise with ignition advance.

Gastester works on the 'hot wire' or thermal conductivity principle. According to this principle, the thermal conductivity of a gas depends on the particular mixture of gases present, and is largely independent of gas temperature. In practice the thermal conductivity of exhaust gas varies only with the amount of carbon dioxide (CO2) that is present. Gastester measures the thermal conductivity of the exhaust gas, and therefore measures its carbon dioxide content. However, since there is a inverse relationship between carbon dioxide and carbon monoxide, as CO2 goes up CO goes down and vice versa. Gastester senses CO2 but displays CO levels. The 'correct' CO level will generally result in improved performance, better fuel consumption, and cleaner more environmentally friendly exhaust emissions.

With Gastester you can tune your car for the way you drive. As shown in figure 1 (from the Bosch Fuel Injection and Engine Management book) the air/fuel ratio can be set for maximum power or minimum fuel consumption, or optimized. Gastester only measures CO, but the levels of hydrocarbons (HC) and oxides of nitrogen (NOx), -- the other pollutants typically measured -- can be inferred from the CO level. These three pollutants are related to the air/fuel ratio as described in the Bosch Fuel Injection and Engine Management book and as shown in figure 2.

Since the CO/HC/NOx relationship is constant and predictable, you simply adjust the fuel mixture until you get a CO value that is less than or equal to your state's CO limit for your make and model car. If your car is in tune and set up to manufacturers specs you can be fairly confident that the hydrocarbon and NOx levels are within limits. If possible give yourself a cushion of at least .5% CO to account for Gastester's accuracy. Note: the level of NOx is also affected by timing advance. The greater the timing advance the higher the NOx level. Referring to figure 2, the ideal air/fuel ratio yields the best compromise for control of CO, HC, and NOx before the catalytic converter (a) or after it (b).