Jay Chan wrote:


My questions a

1. Where does the engine get air when it is under load and the
throttle valve is somehow closed? Is there a big air leak somewhere?

If there's no snow, I guess you aren't running it under a load. It
shouldn't take much throttle to run the engine pretty fast without a
load. If there's an air leak, it would take even less throttle opening.

2. Where is the likely air leak? There is no gasket between the
engine air intake and the carburetor. I don't see a gasket there, and
the Technical Manual doesn't show there is a gasket either. May be I
should try adding some gasket in a tube kind of thing? Other than
this, where else is the likely air leak? Does this mean that I need
to fully disassemble the whole engine block?

I can't remember if air can be sucked in past a cylinder-head gasket.
Why not take a syringe and squirt water around the carburetor and
cylinder head? If you can affect the engine speed that way, you've
found an air leak.

3. The fact is that I can keep the choke at full open after I have
adjusted the mixing needle. Does this mean that I have no problem
getting fuel from the mixing needle? Does this also mean that dirty
carburetor is not an issue here?

There could be a passage to add a little gas at low throttle settings.
That part could be clogged. (I don't know if your carburetor has such a
passage.)

4. What is the problem of running this snow thrower as is? I mean
running it in full open choke, with the speed lever at high speed, but
the throttle valve is somehow closed. Does this mean that the snow
thrower will run slow and cannot throw the snow to the proper
distance? Sorry, I don't have any snow on the ground to test this.

If it's an air leak, the engine may run rich when the throttle stays
open to throw snow. With the throttle open, the air leak would matter
less and the rich adjustment of the mixing needle would matter more.

By the way, can you show me a link to the tachometer that you use to
connect to the spark plug? May be I am not using the correct key
words to search for it because I cannot find it in the net.

I may have found something better, a vibra tach. You put it against the
engine and adjust it so the reed vibrates the most.