You’ve just finished a beautiful, even cut on the front half of your lawn. The sun is warm, and you’re feeling productive. You stop for a quick water break, only to find that when you go to restart your mower, it simply won’t turn over. The engine cranks but refuses to catch, leaving you frustrated and staring at an unfinished yard. This common headache is often a classic case of a hot-start issue.
If your Craftsman lawn mower will not start when hot, you’re not alone. This problem is incredibly common with small engines and is almost always related to a few specific components that are sensitive to heat. The good news is that with a little systematic troubleshooting, you can often identify and fix the problem yourself. Finding the right Craftsman Lawn Mower Will Not Start When Hot: Solutions starts with understanding what happens under the hood as the engine temperature rises.
Why Heat Causes Starting Problems
An engine that starts easily when cold but refuses to start when hot points to a failure in one of the core systems: fuel, air, or spark. As your mower’s engine heats up, metal components expand. This tiny expansion can be enough to close already-tight tolerances, preventing a valve from closing fully or causing an electrical component to fail under the increased thermal load. The issue typically reveals itself after a short shutdown, not necessarily while the engine is running.
Key Areas to Check for a Hot-Start Issue
Let’s walk through the most likely culprits, starting with the easiest and most common fixes. Always ensure the mower is on a flat, level surface and the spark plug wire is disconnected before you begin any inspection.
Inspecting the Spark Plug
This is very often the primary culprit. A faulty spark plug, or one with an incorrect gap, can fail to produce a strong enough spark when it’s hot. Carefully remove the spark plug wire and use a socket wrench to remove the plug itself. Check the electrode for excessive wear, heavy carbon buildup, or cracks in the porcelain insulator. If it looks dirty or damaged, simply replacing it with a new, properly gapped plug specified for your model can solve the problem immediately.
Evaluating the Fuel System
Heat can cause vapor bubbles to form in the fuel line, a phenomenon known as vapor lock. This disrupts the flow of gasoline to the carburetor, starving the engine of fuel. Check your fuel cap to ensure the small vent hole is not clogged. If it is, the tank can create a vacuum that prevents fuel flow. Also, consider the fuel itself. Old gasoline that has been sitting in the tank for months can break down and form varnish that clogs the tiny jets in the carburetor, a problem exacerbated by heat.
Your Action Plan for Craftsman Lawn Mower Will Not Start When Hot: Solutions
When your hot mower won’t restart, a quick diagnostic trick is to check for spark. Remove the spark plug, reconnect it to the plug wire, and lay the metal body of the plug against the engine block. Have a friend pull the starter cord (or turn the key) while you look for a bright blue spark. No spark? You’ve likely found your issue. If you have spark, the problem is probably fuel-related. In many cases, letting the mower cool down completely will allow it to start again, confirming a heat-related failure.
When to Seek Professional Help
If you’ve checked the spark plug, fuel cap, and fuel quality without success, the issue may be more complex. A failing ignition coil is a very common cause, as its internal resistance can change with heat, killing the spark. Valve clearances that are too tight can also prevent the engine from starting when hot. These diagnostics and repairs often require specialized tools and knowledge, making a trip to a small engine repair shop a wise next step.
In summary, a Craftsman mower that won’t start when hot is typically suffering from a faulty spark plug, a clogged fuel system, or a failing ignition coil. By methodically checking these areas, starting with the simplest, you can usually get your mower back to a reliable state, ready to tackle the rest of your lawn, even on the hottest of days.