On Dec 14, 6:26*pm, E Z Peaces wrote:
hr(bob) wrote:
On Dec 14, 4:05 pm, E Z Peaces wrote:
Jay Chan wrote:
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?
Where grass wasn't heavy, I used to throttle my mower down to reduce
noise an save gas. *Now my mower has only one speed.

I think manufacturers have found that engines that can't be run slow
have fewer warranty claims. *Keeping the RPMs up can mean better
lubrication and cooling.

It also sounds like the throttle spring is crazy in its operation.
The throttle spring should keep the throttle closed and the control
should work against the spring to open the throttle. *That seems to
not be what the original poster described. *ALso *If the carburetor
has really beeen cleaned , then an air leak beteen the curburetor body
and the manifold or the manifold and the main engine block is suspect.

Bob Hofmann

The opening and closing at 60% choke makes me think the problem is an
air leak. *With 80% choke it gets a good no-load mixture. *With 60%,
it's too lean, so the engine slows and the governor opens the throttle.
* With the throttle open much wider, the air leak matters much less.
The mixture is better, the engine speeds up, and the governor closes the
throttle. *Then it's too lean. *Vicious cycle.- Hide quoted text -

- Show quoted text -

I think you are probably right.

I disassembled and cleaned the carburetor for the second time. This
time I soaked the main part of the carburetor (the one that has many
holes in it) in carburetor cleaner overnight, and then I used
compressed air to blow all the holes in the carburetor (especically
the holes where the "high speed mixing needle" is, and I observed that
the compressed air could force the carburetor cleaning solution
through the holes. It is all clean. But, the engine still exhibits
the exact same problem. I have a feeling that this problem has
nothing to do with the carburetor being dirty or not. Actually the
carburetor was not that dirty to begin with even before the first
cleaning. It is no where near as bad as those dirty carburetors shown
in YouTube.

I begin to feel that your "air leak" suggestion is probably right
because you seem to be able to explain why the throttle valve behaves
like what it does now.

Although cleaning the carburetor doesn't seem to help, I think I have
found a way to workaround the problem. I turn the "high speed mixing
needle" half a turn more open than what the manufacturer suggested,
and then I find that I can keep the choke at full open, and the engine
doesn't stop, and the throttle valve doesn't exhibit the opening and
closing cycle. Therefore, "may" be the problem was as simple as a mis-
adjusted mixing needle. But I am not sure for the following reason:

When the engine speed lever is at full throttle, and the choke is wide
open, and the engine is not under load, I see that the throttle valve
is almost fully closed. I don't know how the engine is getting air
under this situation because the throttle valve plate doesn't have any
hole in it. The air must be coming from some where. I thought the
engine might not need that much air when it was not under load. But
when I put the engine under load, I see that the engine speed up and
the throttle valve briefly open. But the engine "sounds" like it
quickly slows back down and the throttle valve goes back to almost
fully closed.

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?

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?

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?

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.

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.

Jay Chan