After replacing the filter & plug, and adding fresh gas, my toro mower w/ a 6 hp Briggs engine just won't run well. At idle and at speed, load or no load, it constantly varies in rpm and starts v. hard. Never a problem until this year, so I'm stumped, especially since I see no idle adjusting screw on the carb. Thanks in advance for any help or tips.
The reason it surges is it's not getting enough gas, the gas is stale or has water in it. Unscrew the jet out of the bottom of the carburetor and clean it and allow the gas in the carb bowl to drain out. Refill with newly purchased gas and be aware that gas for small engines should not be kept more then 30-45 days. I work on these units for a living and 70% of what we see are fuel related issues.
Also, the choke should never be on all the time. If you have a primer on your motor, it's doubtful you would have a choke. Perhaps you are looking at the throttle plate.
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Re: hard starting and poor running
Try running the engine without the filter and check if the idle would smoothen, maybe a little high. If problem persist, then it would be fuel delivery problem. If the idle is constant (but high), then some sort of blockage on the air filter or a vacuum leak.
Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.
Good luck and kind regards. Thank you for using FixYa.
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Try adding a good amount of Berryman's ChemTool in the tank and operate the throttle without the choke while cranking a few times. Let it sit overnight and try again. No need to worry about dilution, the engine will run on straight Chemtool. Always run all fuel out before storing for the end of the season to prevent gum and varnish in the carb.
Carb is dirty and before you tear it really apart take the fuel bowl off if it has one and clean it real good and blow the dirt out of the fuel jet which is the bolt that holds the bowl on .That may be most of your problem. Drain the old gas and replace with fresh as well. Won't hurt to run some cleaner through as well.
Clean or change air filter. Clean, gap or change spark plug. Empty gas tank add fresh gas with Stabil. When spark plug is removed pull rope several times to blow out cylinder. Spray starter fluid in spark plug hole before replacing spark plug. Clean outside of carb so choke works freely. Spray starter fluid into carb breather hole with air filter removed and try to start. if running replace air filter and cover. If no start disassemble carb and clean. If no start replace carb.
The inlet needle in the carb is leaking, it may be the activating arm has stuck, remove the float bowl and gently work the float up and down a few times, make sure the needle is moving. Failing that replace the needle valve.
since you have the cover off, clean and spray the governor linkage with WD40, Often there is a lot of
dirt and grass restricting the movement or airflow to the plastic vane that controls the throttle,this has to move freely in order to engine speed, be sure to clean the inside of the cover,always check the flywheel shear pin, if it is bent even slightly, replace it.this pin keeps the engine in time, therefore if the pin is not perfect the timing suffers, poor operation, hard starting etc
One other thing to check is the choke operation, does it open fully after the engine starts?clean with carb cleaner.
Change your air filter, spark plug, fuel filter, and oil. Then make sure the gas is fresh. Gas starts going bad after a month. Spray carb cleaner in hole underneith the fuel filter. Oh yea dont put more than 20oz of oil in it.