Arlen Holder wrote:
> It's a Honda lawnmower I'm asking about, which is about 10 years old, but
> which runs fine most of the time.
>
> I replaced the plug, ran a tank of fresh gas, and cleaned the filter, and
> yet, it "wheezes" like it's breathing, normal rpm, and then slower rpm and
> then normal rpm and then slower rpm and then normal rpm and then slower
> rpm, etc, ad infinitum.
>
> The interval is only about a second or two at most for this
> stoichiometric:lean stoichiometric:lean stoichiometric:lean cadence to
> occur and the stoichiometric:leancycles are quite regular.
>
> The (California) carb on this thing is not adjustable (AFAIK), and the
> choke shuts off in seconds as it's merely a slider that glides back in
> place in a couple of seconds after initial activation.
>
> Even after a half hour of running, the stoichiometric:lean wheezing only
> gets slightly less pronounced, where the stoichiometric:lean wheezing I'm
> talking about is when there is no load (e.g., it's sitting level on a
> sidewalk). (Under load, it's harder to tell, but there's no "speed"
> adjustment given I have the throttle bar on the handle taped tight in the
> always-full-on position.)
>
> I'm thinking it's all in the carb - i.e., choke and/or throttle...
>
> So I guess it "could" be the throttle bar vibrating, but I don't see how;
> and I guess it could be the throttle cables vibrating I guess, but again,
> what can I do about that?
>
> What could be causing this cyclic RPM change?

Sounds like a blocked jet. On the typical non adjustable carb they are
set up to run lean and draw through both the idle circuit and the main
circuit to get enough fuel to run properly at full rpm. One jet starts
to gum up and you get rpm surge. Two choices for repair, pull the carb,
take it apart and clean it in a carb bath or ultrasonic cleaner. Or
replace it with one of the hundreds of replacements out there.

You could try adding some seafoam to the fuel and see if you can clear
it out that way but it really depends on just how plugged it is as to
whether that will work.
--
Steve W.