Why do mowers have primer bulbs?

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snipped-for-privacy@fmbcad.com wrote:

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. HTH
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[posted and mailed]

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.
Matt
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Thanks for the info.
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