Jay Chan wrote:
I have a John Deere Snow Thrower Model 522 that has a Tecumseh engine
(model HSSK50). Since several years ago, I have been having a problem
running its engine without any choke. It will run if I put it on Full
Choke or at more than 60% choke. But the engine will stop if I reduce
the choke to less than 60%. I was under the impression that this
problem means that the carburetor needs to be fully cleaned. Today, I
finally have the carburetor fully disassembled and sprayed and soaked
the components in carburetor cleaner. And I also replace some parts
with parts from a repair kit. But after I have cleaned it and re-
assembled it, I find that the problem is still there.

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.

Jay Chan

It's either too much air or too little gas. If it's too little gas from
varnish or corrosion in a passage, maybe cleaning didn't remove it.
I've had good luck with Sea Foam. I don't understand why it works. It
seems to be mineral oil, rubbing alcohol, and a little ether, and you
add just a little to your gas.

I think the problem isn't that. I think it's too much air. If it's too
much air, you will need less choke when the engine is under a load
(actually throwing snow). I'd look for a place air might leak in, on
the carburetor or between the carburetor and the intake valve. Loose
fastener? Bad gasket? Disconnected tube?

I had a tachometer that you could clip around the spark-plug cable to
pick up pulses. If your magneto sparks every revolution, you'll get a
reading that's twice as high as the RPMs. I had another tachometer that
was a strobe light. You'd make a mark on a rotating part, start the
engine, turn the strobe down slow, and speed up the strobe until the
mark appeared to freeze.