SCAG zero-turn mowers lose power and bog down when old fuel causes fuel restrictions in the carburetor, fuel filter, or fuel lines.
A loss of power may also be due to a bad spark plug, wrong engine oil level, poor air circulation around the engine, or overworking the engine.
Follow the safety precautions in your SCAG operator’s manual. Remove the ignition key and spark plug boots before you begin making any repairs.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
10 Reasons Your SCAG Zero Turn Mower Has No Power
1. Old Fuel
Fuel that has been sitting around for long periods can break down and become less effective. It can develop gummy substances and deposits that can cause blockages in your fuel system which can result in a power loss.
Because of this, only purchase the amount of fuel you are able to consume within 30 days. Add a fuel stabilizer to keep gas stable longer and reduce moisture in the fuel system.
SOLUTION: Drain your bad fuel into a container for recycling. Refill with fresh fuel. Gasoline-powered SCAG mowers use unleaded gasoline that has a minimum octane rating of 87 and a maximum ethanol content of 10%.
Do not use a fuel with a higher ethanol content because ethanol is not good for small engines. Learn more about the right fuel to use in your Gravely zero-turn and stabilizing your fuel with an additive in my other articles.
2. Dirty Carburetor
The carburetor regulates the fuel and air pulled into the cylinder for combustion. The substances left behind from running gas can clog fuel passageways preventing the carburetor from providing the fuel needed to run.
When this happens, the dirty carburetor can cause your mower to experience a loss of power. Clean a carburetor that isn’t allowing fuel to get to the cylinder.
SOLUTION: Before you tear your carburetor apart to clean it, confirm you are getting fuel to the carburetor. Next, remove the air filter and spray carburetor cleaner into the air intake.
Start the engine to see if it runs better. If the engine runs strong and then begins to lose power or die, you need to clean your carburetor. Refer to the article to find step-by-step instructions to clean your zero-turn carburetor.
3. Clogged Fuel Filter or Fuel Lines
Dirt and the substances left behind by running old fuel can cause your fuel filter to become plugged and your fuel lines to become clogged. This fuel restriction can cause your SCAG zero-turn to feel a loss of power and run sluggishly.
Check for clogs in the fuel lines by starting and stopping fuel flow using the fuel shut-off valve located on the bottom of your fuel tank or by crimping the fuel line. Stop your fuel flow.
Remove the end furthest from the fuel tank of one section of the fuel line and place it in a container. Start flow to check for blockages. Continue checking other sections of the fuel line.
SOLUTION: When you find a clogged fuel line, remove the section of the line and spray carburetor cleaner into the line. This should help loosen up the clogs.
Follow this by blowing compressed air through the line to free the obstruction. If you cannot remove the blockage or you notice your line is dry and cracked, replace it with a new fuel line.
Check the fuel filter and replace a plugged filter.
4. Dirty Air Filter
When you feel you are losing power when running your SCAG, check your air filter. A plugged air filter can cause a power loss.
Your engine requires air to run. When it no longer gets the air it needs, the engine may run sluggish, overheat, and possibly quit. Regularly check your air filter’s condition.
SOLUTION: Inspect and clean a dirty air filter. If it is extremely dirty or damaged the filter must be replaced.
How to Clean Your SCAG Zero Turn Paper Air Filter Element
- Remove the air filter from the air filter housing.
- Wipe out any remaining dirt in the housing with a dry cloth. Be careful not to allow dirt to fall into the air intake.
- Tap your air filter against a solid surface to knock as much dirt loose as possible.
- Hold your filter up to a light source.
- Reuse your filter if you can see light through the paper element and it is not damaged or extremely dirty.
- Replace with a new filter if you can’t see light through the paper element.
5. Bad Spark Plug
A fouled spark plug in your zero-turn can cause an intermittent spark that can cause a loss of power. Inspect your spark plug for signs of carbon buildup, wear, or damage.
SOLUTION: If you find a dirty or damaged spark plug, I recommend replacing it with a new one to ensure you’re running a good plug in the mower.
If you choose to, you can attempt to clean it with a wire brush and reuse it if the spark plug is in good condition and not very dark in color.
Make sure the electrode gap meets the specifications of the engine manufacturer and the spark plug wires are securely attached.
6. Low Engine Oil Level
When your SCAG zero turn doesn’t have enough engine oil in the crankcase, the engine will experience a loss of power. The lack of lubrication from not having enough oil causes increased friction.
This friction builds heat and causes the engine to get extremely hot and suffer a loss of power.
If a low engine level isn’t caught quickly, the increased heat will cause internal engine parts to melt. This can result in a significant engine repair bill or possibly an engine replacement.
Routinely check your engine oil level before each mowing. This doesn’t take too much time and can help you catch oil leaks or engine problems early.
Always run the correct amount of oil in your engine. Not doing so can cause running and overheating problems.
SOLUTION: When you find your engine doesn’t have enough oil, add oil to bring the level to the manufacturer’s recommended level.
If you continue to have engine problems, running your zero-turn mower with low engine oil could have caused internal damage that needs to be diagnosed by an experienced small engine mechanic.
7. Too Much Engine Oil
Overfilling the crankcase with engine oil will cause your engine to smoke. Increased pressure builds as a result of too much engine oil and oil can be pushed into the cylinder through the valve train.
When this happens, a bluish-white smoke is emitted when the oil burns in the cylinder.
SOLUTION: Continuing to run your SCAG with too much oil can cause seal damage, the engine to hydrolock, and a bent piston rod. Correct an engine with too much oil by removing a little oil.
This thick cloud of smoke can plug your air filter causing running issues because your engine isn’t able to get the clean air it needs. Check your air filter and your spark plug, and clean or replace them if needed.
8. Poor Air Circulation Cooling
Your engine needs to be kept cool to prevent it from overheating and losing power. Make sure your engine has good air circulation by removing any grass clippings, dirt, and debris that may be collecting around your engine.
SOLUTION: Remove all the debris that has been collected under your engine shroud.
9. Engine Cooling Fins are Dirty
The cooling fins are essential to circulating air around the engine to keep it cool. Just like you need to remove debris from collecting around your engine so your engine doesn’t overheat and experience a loss of power, the same is true of your cooling fins.
The fins can become plugged with mud and grass clippings inhibiting the amount of air is it able to push to the engine.
SOLUTION: Clean out debris around your cooling fins and replace any broken fins to make sure it is functioning properly.
10. Too Much Load Placed
When too much load is put on your engine, you can lose power. This extra load requires the engine to work harder. These are items that can put your zero-turn under load:
Ground Speed is Too Fast for Mowing Conditions
Mowing your lawn at too fast a speed can put extra load on your SCAG zero-turn. Slow down the speed to match your mowing conditions. For example, your engine works harder to mow thick lawns over thinly covered lawns.
SOLUTION: You need to operate your zero-turn at a slower speed when mowing thick lawns. Operate your mower slower when on inclines. Mowing inclines makes your engine work harder.
Mowing Wet or Tall Grass with Your Mower
When mowing wet or tall grass, you are making your engine work so much harder than mowing dry grass with a manageable length. Mow your grass when it is dry.
This puts less load on your engine and reduces the amount of grass clippings clumping and collecting under your mower deck.
SOLUTION: It is best to mow regularly to prevent your grass from getting excessively tall. When mowing tall grass, adjust your mower deck to its highest setting for the first cutting and then lower the deck for the next cutting.
Avoid mowing in these conditions if possible. If you do need to mow this type of grass, slow down your zero-turn speed to not overwork it.
Grass Buildup Under Your Mower Deck
Keep your mower deck clean so the blades can spin freely. When dirt and grass clippings plug the mower deck, the engine is required to work hard to turn the blades through the buildup with each revolution.
SOLUTION: Regularly scrape your deck to remove debris. Avoid mowing in wet conditions as the grass is more likely to build up under your deck.
Not only does this extra debris under the deck cause your engine to work hard and lose power, but it also causes your SCAG mower to give you a bad cut.
Running Dull Zero Turn Mower Blades
What further magnifies the lack of power received when mowing with a clogged mower deck, is mowing with dull mower blades and a clogged mower deck.
SOLUTION: Check your blades and sharpen or replace them if needed. You can find more information on inspecting your blades and the sharpening process here.
Still Experiencing Problems with Your SCAG Lawn Mower?
Own a lawn mower long enough, you’ll start running into problems with it starting, not continuing to run, smoking, leaking gas, giving a bad cut, vibrating, or another issue.
To help you save time and money, I have put together a guide to help you troubleshoot the next problem that develops on your mower.
You can find this guide at Common SCAG Lawn Mower Problems & Solutions.
If you are unsure how to perform diagnostics and repairs on your lawn mower safely, it’s best to have a professional complete the repairs.
This will help you avoid personal injury or additional damage to the mower. Your local SCAG lawn mower dealership or lawn mower repair shop will be able to help you solve your problem.