Weak or no spark

Check all of these parts
Solution 1:
Spark Plug
Solution 2:
Carburetor
Solution 3:
Carburetor Repair Kit
Solution 4:
Old or Bad Gasoline
Solution 5:
Fuel Pump
Solution 6:
Start Switch
Solution 7:
Flywheel Key
Solution 8:
Ignition Coil
Solution 9:
Fuel Filter
Solution 10:
Safety Switch
Solution 11:
Recoil Spring
Solution 12:
Recoil Starter
Solution 13:
Recoil Starter Pulley
Solution 14:
Rewind Pulley and Spring
Solution 15:
Rewind Spring

For more information on the topic visit this link: https://www.repairclinic.com/RepairHelp/How-To-Fix-A-Lawn-Mower/79-324--/Yard-Machines-Lawn-Mower-Won-T-Start

Good luck and happy fixin :D

These small engines have ignition units that work off speed of rotation, so once the engine starts the spark increases, if there is a spark there is a weak spark there I would say its ok, you maybe have a fuelling issue, does the plug get wet after a few cranks?

bad ignition switch

Pulley ? What pulley?
If you mean the recoil starter pull cord is stuck it might be a simple fix. Did your machine tip over on its side?
If it did oil often flows into the cylinder. Just remove the spark plug. The recoil cord should pull easily and oil will spurt out the spark plug opening. Pull until oil stops coming out. Check your oil level. Replace your spark plug and see if she starts.

remove spark plug .put new one on to plug lead make good earth.turn ign. on pull over check for a good blue spark.

FOLLOW this steps and fix it. Merry Christmas

Spark Plug

Every chainsaw relies on a spark plug to ignite the air-fuel mixture for proper combustion. Over time the electrode on the spark plug will burn away and the engine does not start. If the engine does not start, remove and inspect the spark plug. If there is any doubt that the plug is working properly replace it.
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Carburetor

If the chainsaw won't start, the carburetor might be clogged or have bad fuel in the float bowl. If old fuel was left in the chainsaw for a long time some of the volatile ingredients may have evaporated, leaving a thicker, stickier product that is more like varnish or shellac. This sticky fuel can clog up the small jets and ports in the carburetor and it can be difficult to burn making it hard to start the engine. The only solution is to drain the old fuel from the float bowl and thoroughly clean the carburetor with carburetor cleaner. If that isn't effective, replace the entire carburetor.
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On - Off Switch

Chainsaws are equipped with an on/off switch. If the chainsaw does not start, this switch might be defective. Check the switch for continuity. In the on position the switch should have continuity.
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Safety Switch

If the chainsaw does no start, the safety switch - or throttle control switch - might be defective. If the switch isn't engaging with the throttle it won't provide enough fuel to the engine and the engine does not start.
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Ignition Coil

If the chainsaw engine does not start the spark plug may not be getting voltage. Power to the spark plug is provided by the ignition coil. The ignition coil is mounted next to the flywheel. As the flywheel spins an electrical current is induced by the ignition coil. If the ignition coil is defective it will need to be replaced, it is not serviceable.
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Rewind Spring

The recoil starter assembly has a rewind spring which spins the pulley backward to rewind the starter rope. If the rewind assembly is broken the rope will not rewind and the engine does not start.
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Recoil Starter

If pulling the recoil starter assembly handle doesn't engage with the engine and the engine does not start. Repair or replace the recoil starter assembly.
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Recoil Starter Pulley

The recoil starter pulley winds up the starter rope when not in use. If the recoil starter pulley is broken or stuck it may not rewind the rope and the engine does not start.

Possible ignition starter switch problem.

I had the same problem, maybe 25MPH top speed and difficult to start. Changed out the old gas, installed fresh high octane-problem was worse.
The ignition system was faulty. Pull a High voltage wire and you should see a bright blue spark and hear a crackling noise. If you see a weak yellow spark, you found your problem.
Could be a bad/weak ignition module-rather famous in a Fiero due to heat exposure. Bad pickup coil in the distributor. I replaced the entire (rusty) distributor with a new/rebuilt unit a long with a new Ignition module. Solved the problem!

There has to be a reasonable spark at hand cranking speed, with most electronic ignitions they work off speed of rotation so you do need to crank the engine at a fair speed, check the air gap between the flywheel magnet and the ignition core, this should be around 0.3mm, if there is not spark at all when cranked well it will be a replacement unit required.

1) Check for spark remove one of the plugs, connect the plug wire to it and ground spark plug base to a good ground , such as the cylinder head , position the plug so you can see the electrodes , crank the engine over , a fat blue spark should be evident. 2)If the spark is good , check for one or more of the following possible malfunctions 1) Obstructed fuel line or filter.2) leaking head gasket(s)3) low compression. If the spark is not good, check one or more of the following a) Weak ignition coil(s) b) Weak CDI unit. c)Loose electrical connections. d) Dirty electrical connections. e)Loose or broken ignition coil ground wire. f) Broken or shorted high tension lead to the spark plug. Difficulty in starting. Check for fouled spark plugs, Improperly adjusted choke, contaminated fuel system, improperly adjusted carburetor,weak ignition unit,weak ignition coil (s), poor compression