Lawnmower engine idling to low - Briggs & Stratton Lawn-Boy 10640 20-Inch 6.5 HP Gas Powered Lawn Mower

According to Amie Taylor on http://homeguides.sfgate.com/lawnmower-revs-up-down-100220.html "Airflow Issues A lawnmower that hunts and surges may be experiencing something as simple as an airflow issue. If the air that the engine requires to run is blocked, especially sporadically, it can cause the engine to slow down. When the blockage moves or clears, the engine may suddenly rev up in response. To fix this type of problem, check the air filter to ensure that it's not clogged with dirt and debris. Check the vented gas cap as well. Both issues can cause reduced or sporadic air flow, and clearing them will fix the problem.
Spark Plug Problems Another problem that can cause revving and dying of a lawnmower engine is a faulty or poorly adjusted spark plug. Check the spark plug to see if the wire is connected to it firmly and not wobbling about. If it is connected correctly, remove the spark plug to see if it's covered with corrosion. If so, a simple scrubbing with a wire brush can restore it to working order. If necessary, replace the spark plug with a new one. Check the spark plug gap with a spark plug gauge to ensure that it's adjusted to the proper setting recommended in your owner's manual.
Carburetor Adjustment A carburetor that's incorrectly adjusted is a common cause of poor engine idling that results in hunting and surging. Fortunately, most lawnmowers have two screws that allow you to adjust the carburetor yourself. One screw controls the idle speed while the other adjusts the idle mixture. Check the manual if you're unsure of the location of the idle adjustment screws. Start the mower and allow it to run for 5 minutes. Then slowly adjust the screws tighter or looser in turn until the mower runs and idles smoothly.
Fuel Problems A particularly simple fix that can be at the bottom of many lawnmower idling problems is old or contaminated fuel. If the fuel has been left in the mower while it was stored over the winter or while the mower has remained unused, drain it and replace it with fresh fuel. If you have gas-powered blowers and trimmers that use a mixture of 2-cycle oil and gasoline, check to see that you've not placed that mixture in the lawnmower inadvertently."

There is a throttle stop screw on the carburetor, turn it counterclockwise to lower engine speed. Check the carburator bolts to make sure the carb. bo

wont have one, thank you California EPA.and stuff L.O.L. .Is that the lawnmower model number? need the engine model number I might be able to help. jackssmallengine.com

this problem you will have to take to a small engine repair shop it is harder to fix or to tell you what is wrong with out hearing it for my self it could be a few things make sure that you find one that the labor rate is low but the quality of work is good...

Hello, This could be an indication your A/C is low on Freon or your Power Steering pump is low on fluid. Both systems are made to increase the idle speed to make the system work better. What happens in the case of the A/C, is the A/C compressor puts a strain on the motor when it engages the electric clutch on the compressor.

The A/C is wired such that when the compressor clutch engages, the engine RPM is increased to maintain the idle speed. The controls do this automatically and when your compressor is low of Freon, there is little resistance and the engine overspeeds. You are burning up your compressor if you lose the lubricant packaged inside it. That noise you hear is a dry compressor.

Turn your A/C or Defroster off and see if the overspeed and the noise stop. The compressor will run in the Defrost cycle too! Eventually your A/C will lose more of the Freon until the low pressure switch cuts the power to the compressor completely.

Some front wheel drive cars have a boost sensor in the power steering assembly for increasing the idle speed when you are turning the steering at low speeds. If the fluid level is low, it tricks the sensor into speeding up the idle to assist steering. Like in the A/C example, you can get overspeed when the fluid levels are low.

I hope my solution is very helpful in fixing your problem. Have your Freon checked or throw in an "OIL Charge" with the proper type of oil for your compressor. Then check your Power steering.

the lawnmower is not designed to idle with a load on the engine, it needs to be operated at full throttle

Is it smoking at idle? or just running ruff?

Check the EGR for leaks.Here is th emost common cause of idle surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake