When you have a Carburetor Car with Poor Starting or Discrete Burnt Plugs, Suspect a Clogged Pilot System!

Remove the air screw and try blowing cleaner directly into the air screw.

Remove the carburetor air screw on the cylinder with low exhaust pipe temperature at idle and spray carburetor cleaner (engine conditioner) on the cylinder.
Foam-type carburetor cleaner is more effective than brake & parts cleaner for carbon and fuel-based dirt.

After spraying until the foam flows back from the screw entrance area, allow some time for the cleaner ingredients to penetrate.

When the pilot system is blocked and idling is sluggish, the easiest solution is to try spraying carburetor cleaner or engine conditioner directly into the air screw area. The textbook response would be to remove the carb from the engine and disassemble and clean it again, but if you know from the symptoms that the problem is only in the pilot system, it is better to try the simplest method possible to reduce the amount of work involved. Remove the air screw and spray the cleaner, which will go to the pilot outlet on the venturi, the pilot jet on the float chamber side, and the slow air jet on the air cleaner side. If there is just a small piece of debris trapped, it will be blown away by the pressure of the spray, and any dirt that was not removed during cleaning may be removed by the cleaner component.

Carefully blow air after cleaning.

Blowing air at high-pressure risks damaging floats and float valves, so keep the amount of air blown as low as possible at low pressure.

After spraying the carb cleaner and waiting a while, you can ruin it by blowing air. At this time, however, be careful how you spray the air. While it is true that you want to blow the clogged debris vigorously if high-pressure air flows into the float chamber, the pressure inside increases all at once and there is a risk of damaging the float and the float valve. Air blowing is effective, but you should remove cleaner components and dirt by squeezing air pressure and controlling the amount of air gun trigger pull well. In this case, simply blowing carb cleaner through the air screw opened the pilot system and the car started idling on all four cylinders without disassembly and cleaning. Not only when disassembling and cleaning was not done completely, but also when dust accumulated in the float chamber or rust that has flowed in from the fuel tank can clog the pilot jet more easily than the main jet, as explained earlier, and can cause idling problems one day. If you encounter such symptoms, you can take the plunge and disassemble and clean the carburetor, but we recommend that you try injecting the carb cleaner directly after checking the effectiveness of the air screw and pilot screw.

When disassembling and cleaning, blow air as carefully as the pilot system.

There are a number of small holes machined inside the carb body, such as air passages, fuel passages, and acceleration pump passages. There is no doubt that clogged pilot jets and main jets affect carb performance and air-fuel ratio, but clogged or dirty passages inside the body also affect air and fuel flow, so it is important to carefully blow air through the internal passages as well as the external surface when disassembling and cleaning.

As mentioned above, cleaning the pilot system may resolve problems with idling after disassembling and cleaning, but before that, it is important to clean the pilot system more carefully than the main system when disassembling and cleaning. The pilot system has narrow passages inside the body, and it is sometimes difficult for cleaners to penetrate and remove varnish that has become clogged due to prolonged neglect. However, as explained so far, the air-fuel mixture and air-fuel ratio in the pilot system are greatly affected by idling and low throttle opening, so thorough cleaning is necessary.

While it is an accomplishment to remove greenish-blue from the jets and needles and varnish from the inside of the float chamber, it is also important to check the condition of the ports inside the body, which cannot be visually confirmed. Since they cannot be seen, it is also effective to carefully blow air after thoroughly penetrating the carburetor cleaner and, for multi-cylinder carburetors, to check for variations in air release before assembly. It is easy to suspect carb setup or engine condition when the spark plugs do not have the same burnt condition, but it is also important to clean and maintain the carburetor body with the understanding that the basic premise is to have the same amount of air and fuel passing through the inside of the carburetor.