In ,
Oren typed:
:: On Sat, 05 Feb 2011 00:20:58 -0500, Taylor
:: wrote:
::
:::
::: My snow blower has a Briggs & Stratton 7.5 hp "Powerbuilt
::: Snow" horizontal engine. It has always need a little
::: choke to run smoothly after it warms up. With no choke
::: it runs, but stumbles slightly. With one click it is a
::: bit smoother, and with two clicks it runs the smoothest.
::: More than that, there is too much choke and the engine
::: will die.

Mal-adjusted choke position; no-choke is bringing it backwards, partly
closing in the opposite direction. Watch the flapper work with air filter
removed. Note: Tuning will be different with air filter removed so don't
forget to account for that.

:::
::: Thinking that perhaps something is clogged in the
::: carburetor/jet, I replaced the whole carb with a new one.
::: The result is exactly the same.

Did you check for full fuel-flow from the tank to the filter and filter to
the carb? Partial plug or kink in the hose can pinch off gas supply partly &
make run lean.

:::
::: I have fresh gas, use Sta-Bil, etc. I'm not overly
::: worried about it, I just use two clicks of choke for best
::: power.

Empty tank & refill with fresh gas newly purchased. If this is last year's
gas it could do that, especially if there is an over abundance of Stabil in
the gas.

:::
::: However, I suspect that I'm not getting the full 7.5 hp
::: with the choke restricting air intake. I'm also curious
::: what the problem is. A repairman said that all engines
::: are tuned lean due to EPA rules. Of course there is no
::: way to adjust the mixture.

I suggest he's blowing smoke; that's still no reason to have the choke to
any position but OFF when the engine has warmed up.

If it has a carburator and burns gasoline, there most definitely IS a way to
adjust the mixture!! Check the carb documentation or the machine's
paperwork.

:::
::: Any ideas what causes this? Is the repairman right about
::: the mixture set overly lean on purpose?

I think he just wanted you off the phone. Irrelevant to what you're having
to do to keep it running right.

:::
:::
:::
::
:: I'd check the air filter and be sure it is clean or new.
:: Does it run better with the filter removed, not needing
:: the choke...
::
:: Also look at the spark plug. Adjust the plug gap a little
:: (open or close it a tad) and see what happens or replace
:: the plug. Make sure you have the correct/recommenced plug.

Better to check/adjust the plug gap to precisely what it is supposed to be.
Usually it's 0.030" for that size B&S in my experience.

::
:: Spark Plug Chart:
::
:: http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

Air filter, fuel filter (if you find water, also the gas tank), choke
flapper needs adjust, lo-speed screw, low-oil shutoff, fuel line partly
plugged, and so on.

Does it start easy and then run rough, or is it also hard to start? Stabil
makes them hard to start, especially if excessive amount is collected in the
carb. bowl.

HTH,

Twayne`