Poor mainframe can't get an answer to his question.
Here ya' go. The old carburators allowed the heat of the day
to push fuel through the engine when not running. This fuel
evaporated into unnecessary pollution. It would also (sometimes)
flood the engine and make it hard to start. The new carbs, in order
to comply with emissions standards, do not allow this fuel to be
pushed through. In exchange for that, you need to prime the
engine with the bulb.
The primer bulb is there for many reasons.
As someone else indicated, a primer is CHEAP, and generally very reliable.
For many years, Briggs and Stratton had an automatic choke on most of
their walk behind mower engines. This automatic choke had many problems
over the years, and was not always reliable. Further, it often OVER
choked, or flooded a hot engine.
Tecumseh had a different idea, they designed a "self-priming" carburetor.
It, too, didn't always work as planned, and was often retrofitted with a
rubber primer bulb on the BOTTOM of the carburetor bowl. Tecumseh
eventually moved the primer bulb to the side of the carburetor and
eliminated the "self priming" feature of their carburetor. Briggs and
Stratton replaced their own auto-choke carburetor with one licensed from
Walbro that had a manual choke, which worked well except for the fact that
many people left the choke on after starting. This created "excess" air
pollution. That Walbro carburetor is the basis for the newer version with
the primer as well.
Despite the fact that over 90% of the air pollution from lawn and
garden equipment comes from spilled or evaporated fuel, the government
has imposed "tailpipe" emission standards on all outdoor power equipment
engines. So many of the manual chokes have disappeared. Honda still uses
a manual choke because their engine runs very lean and their choke is
partially self relieving. This means the choke opens itself partially once
the engine is running. Both Briggs and Stratton and Tecumseh still offer
the mower manufacturer the option, for an additional charge, of a choke on
a very small number of engine models, but the equipment manufacturers
generally don't spend the extra money.
Rider mower engines are different. They all still have chokes, either as a
part of the throttle control, or as a separate control. Since you have to
be in the seat to start and run a rider, it would be difficult to use a
primer on these (not impossible, but nearly). Kohler has actually begun
offering electronic fuel injection (Honda does NOT as yet) on rider mower
engines. I believe that eventually all riders will have EFI just like all
cars have had since the mid-80's.
The EPA rules are also why you are beginning to see 4 cycle line trimmers
on the market. 2 cycle engines, where you mix the oil into the gas, are too
dirty to meet the rules for most application. And California, as always, is
leading the way to even stricter rules.
I believe that eventually the hand held equipment will be almost entirely
rechargeable electric in a few years, with the only forseeable exception
being chain saws. It could well pass that even the walk behind consumer
mower market could end up all rechargeable as well. After all, GE sold
rechargeable GARDEN TRACTORS from around 1969 to 1974. They sold the entire
product line to Wheel Horse, who conitnued to sell them until 1981 or '82.
They are highly collectable today.
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