Now that I have the carburetor cover removed, I can see the arms of the various valves of the carburetor in action. I notice these:
1. When the engine is running at Full Choke, the throttle valve is open. I think this is normal because I am running the engine in full throttle.
2. When the engine is running at 80% choke, I notice that the throttle valve is nearly closed. This is odd because I have set the throttle lever to Full (Fast); the throttle valve seems to be closing by itself. The engine "seems" to be running fine. But I have a feeling that the engine "sounds" like it is running in slow throttle. Is this normal? What's sucking the throttle valve from Full to Slow?
3. When the engine is running at less than 60% choke, I notice that the throttle valve is opening and closing, opening and closing, and so on ... all by itself. Therefore, the engine is speeding up and then slowing down, speeding up and then slowing down, and so on... This opening and closing cycle is like just 1.5 seconds. This opening and closing cycle will increase to something like 2 seconds if I slightly open the choke just a bit (something like 55% choke). I don't think this is normal. But I don't know what is causing it to automatically closed and then opened again.
4. When the engine is running at 50% choke or lower (less choke, more open), the engine will stop, and the throttle valve will go back to the full open.
What is going on here? I have checked the spring that keeps the throttle valve at full open (and is the one linked to the throttle lever), and it seems strong enough to keep the throttle valve at full open position if the throttle level is in the Full (Fast) position. What is so powerful that it can suck/push this throttle valve to close?
Is the carburetor needed to be cleaned one more time?
One additional question: The Tech Manual from John Deere asks me to make sure the engine is running at 3600 rpm when the engine is set at high-speed mode. I am under the impression that we don't want the engine to spin too fast and burn itself. That's why we want to keep its rpm to not more than a certain limit. This means I need a tachometer. But tachometer seems to require seeing or touching the spinning part of the tachometer in order to measure the rpm. Unfortunately the engine is fully enclosed, and I cannot see the spinning part of the engine. Is there any tachometer that doesn't require seeing or touching the spinning part of the engine? Can we measure the rpm by timing the number of sparks that the spark plug makes?
Thanks in advance for any help.