A “vapor locked” lawn mower can be a frustrating experience. This situation is also commonly referred to as “flooding” the engine. When you have a vapor locked lawn mower, the engine will not start. Let’s look at the cause and talk about how to fix it. The good news is that it’s quite a simple repair.
What is a Vapor Locked Lawn Mower
Combustion engines run on a air/fuel mix at the right proportion to be able to ignite. If the fuel is too lean or too rich, the proportion is off and ignition will be inefficient, if at all. In the case of a vapor locked lawn mower, the engine becomes flooded with too much fuel/ fuel vapors. In normal operation, the piston travels in the cylinder and compresses this air/fuel mix. The compression, when combined with the spark from the spark plug, creates the combustion to operate the engine.
In the case of a vapor locked lawn mower, there is too much vapor in the combustion chamber. This prevents the cylinder from compressing, or creating the compression that’s required. Because the compression is inadequate, the engine will not fire. Oftentimes, the situation exacerbates itself because each pull of the recoil introduces more fuel into the chamber that’s not being fired. The only way to solve this problem is to clear the vapor lock, or “unflood” the engine.
What Causes a Vapor Locked Lawn Mower
This is dependent upon the type of engine, but as we just mentioned, the root cause is too much fuel. Perhaps you primed the bulb a few too many times. Each successive pulse of the primer bulb introduces fuel into the combustion chamber. The intent is to ease ignition, but too much fuel will cause the vapor locked condition.
Also, if you attempt to start the engine with too many pulls with the choke in the on position, this can cause a vapor locked lawn mower. When the engine is “choked,” the air passage is narrowed down. This reduces the amount of air coming into the engine. Since the fuel amount is remaining the same, the resultant proportion will be “richer.” Every time you pull the recoil, the richness of the mixture is increasing. Eventually, you will end up with a vapor locked lawn mower.
A good rule of thumb is to only pull the recoil with the choke in the on position 3-5 times. If it does not start, clear the vapor lock (and figure out why it didn’t start!)
Choking the engine can also be problematic if you use it on a warm engine. Normally, choking the engine only assists with starting the engine when it’s cold. When the engine is warm, it does not need to be choked. Let’s say you start your lawn mower and go about cutting. After a few minutes, it’s warmed up and you have to stop to move a chair in your yard. So, you shut the engine off and move the chair. When you go to start it, if you re-choke the engine, it could possibly flood because the choking is not required.
How to Tell if you Have a Vapor Locked Lawn Mower
Luckily, it’s readily apparent to tell if you have a vapor locked lawn mower. If you have a manual pull start engine, each successive pull of the recoil will become more difficult. Eventually, the recoil might not even rewind. This is because the piston is working harder and harder to compress a higher proportion of air/fuel mix than it was designed for.
For an electric start, you can hear the engine “chugging” and working harder to start. It’s quite easy to damage a starter if the engine is vapor locked.
Tools Needed (Commissions Earned)
How to Fix a Vapor Locked Lawn Mower
So now that we know what a vapor locked lawn mower is and what causes it, how do we go about fixing it? Fortunately, it’s a simple process.
The simplest method is to remove the spark plug. With the spark plug removed, either pull the recoil or activate the starter motor. Since there is no compression, the extra air/fuel mix can escape through the plug hole. This is the fastest way to fix a vapor locked lawn mower.
The other option is to simply turn the choke to the “off” position. With the choke off, the engine will introduce more air into the combustion chamber. Each successive pull of the recoil will gradually bring the air/fuel mix into the right proportion. Eventually, it’ll reach that perfect point where it can fire. While this method does work, it is a bit more laborious than simply removing the spark plug.
Remember
Limit the use of the choke in your lawn mower engine for only when it’s necessary. Don’t use it on a warm engine, and limit the pulls on a recoil when the choke is engaged. Also, follow your owner’s manual for how much you should be priming the engine when starting. These simple steps will prevent you from experiencing a vapor locked lawn mower.
For those of you how are interested in a video of the process, here’s a link to a good one.