Why starting problem in bl410, i changed sparkplug too

If it is a 2 cycle motor, check the spark arrest or screen in the muffler. It is a fine screen and the oil in the exhaust leaves a carbon buildup that will plug up the screen. It can be cleaned with a brass wire brush or carb cleaner.

Bolens BL410 21BK410G163 Tiller Parts
Try that out

A safe gap is the width of a business card

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1. check the spark plug
2. check out youtube video
How To Troubleshoot Your Weedeater to crank every time

How old is it? Does it show a spark when you remove plug an hold against engine while pulling cord? Did you replace plug? It is the most common problem. Remove the stop wire an try to start, if it does or you see spark the switch is bad. I would check put these things before replacing module.

change your sparkplug bus use a BR9SE sparkplug

Spray starter fluid in the air filter. This should work.

check the fuel cap's vent hole

Hi and welcome to Fixya. The symptoms your describing are typical of what happens when the engine experiences fuel starvation.

It can be caused by a clogged fuel filter screen located at inside the attachment point of the fuel line manifold on the carb. Turn off the fuel and remove the mounting bolt for the fuel mainfold. Very carefully remove the plastic screen inside the manifold and clean off the debris that has built up on the screen.
If the screen was visibly clogged you probably have solved your problem. Just make sure you re-install the screen when re-connecting the fuel line manifold.

If the screen was not clogged then check your fuel lines for cracks. Air being introduced into the system will cause the same symptoms you describe.

If the problem persists then there is the possiblility that the needle and seat are partially blocked inside the carb itself on the bottom of the carb body after you remove the bowl. (Usually not the problem) However the bolt that holds the bowl on has 1 or 2 holes in it that can also clog and they must be clear.

And finally there is a BRASS jet that unscrews with a screwdriver in the bottom of the long draft tube (way below the throttle slider / needle) that gets clogged. Unscrew the brass jet and force air from the threaded end to clear the orifice.

By this time you probably figured out the float comes off with the bowl. note which side is UP! Also DO NOT adjust the float level it is preset. u|Unless you bent the float control arms it does not need adjusting.

Turn on the fuel... and start the unit after re-assy and it should run just fine. You should be tilling real soon!