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Polaris Sportsman 500 Dies When Accelerating: Fix

The Polaris Sportsman 500 is a serious trail quad, offering lots of power and good traction. But there’s one issue preventing you from riding this aggressive 4×4 – it dies when accelerating. You may have tried everything, such as replacing the carb or even the entire engine. So, you may be wondering why your Polaris Sportsman 500 dies when accelerating.

The reason the Polaris Sportsman 500 dies when accelerating often comes from the CDI box, which is used to pass electrical current to the spark plug and ignite the engine. Replacing it with a Polaris CDI box should fix the problem. If not, check other parts of the quad.

Most people would first think the issue relates to the carburetor, which controls fuel and air entering a motor. However, many have discovered the cause of the problem to be electrical – more specifically, the CDI box.

Yellow ATV Driving on a Trail

Polaris Sportsman 500 Dies When Accelerating

This can be a frustrating issue, especially if you don’t know why it happens. Keep reading to learn more about this problem, and other things you can try if replacing the CDI box doesn’t help.

What Is Inside a CDI Box?

A typical Capacitor Discharge Ignition box consists of a small transformer, a triggering circuit, a charging circuit, and the main capacitor. The rectifier found inside the charging circuit stops capacitor-discharge before the moment of ignition.

Typically, it controls the factory safety kill switches, timing, the spark, and the rev limiter. Depending on the ATV’s make and model, the CDI box configuration can differ and control other things aside from what was mentioned.

What Are the Symptoms of Bad Polaris CDI Box?

When a Polaris Sportsman 500 idles but dies, it can point to different things, such as misfires, starting issues, rough running, and even a stalling motor. The below signs can help you determine if the problem is from the CDI box:

  • A bad CDI won’t fire at all since everything goes through the box to fire the motor.
  • Ignition leads will shorten if you spray a bottle of water on them.
  • Frayed wires or loose spade connectors can typically be remedied with a little pinch and some dielectric grease. If this doesn’t change anything, then consider it a symptom.
  • A cooked battery can usually be traced back to a defective rectifier/regulator.
  • Carboned plugs flood the carburetor and point towards a faulty CDI box.
  • Testing your ignition coils with a multimeter gives results outside of the secondary resistance parameters indicated in your manufacturer specifications.

Causes of Restricted Acceleration

While the following usually cause the Polaris Sportsman 500 to die when accelerating, these should not always be the first set of things to inspect. Still, understanding where these problems come from and how to resolve them will not only save you money on repairs but also valuable time:

1. Stator or Coil Failures

A bad source coil in the stator causes the CDI to stop running. A DC conversion kit is a good replacement for the stock CDI box as it bypasses the defective source coil. However, symptoms for this cause normally overlap with electrical wiring or engine compression problems. The best way to find the culprit is to run tests and single out the probable cause one at a time – starting with the compression test, which is the easiest, followed by wiring inspection.

For engine compression, perform an initial test when the engine is cold. When it dies out a second time, test it immediately again. Compare the two results. If the second is significantly lower than the first, you might have found your problem. If this checks out, inspect wiring harnesses that might contact hot surfaces like the exhaust. Also, check if the cylinder head has not been melted or chaffed in any way.

2. Carburetor

The carb is usually the first thing owners suspect as the main cause. Symptoms can get severe to where the carb would only run with the choke on/off or with carb cleaner sprayed down its throat. Some would often jump into replacing bolts, bushings, and the rubber diaphragm at the first sign of a carb problem. They would often forget about giving it a new carb kit when cleaning it out. The needle and seat alignment are often overlooked too, which is the only reason for the impeded throttle response of your Polaris Sportsman.

Note that for Polaris 500s with CV carbs, you have to maintain a certain amount of vacuum to operate the slide properly. This necessitates running a lid and changing the jets. These carbs are very sensitive to airbox changes. Running a new carb kit and modded airbox may take some testing to get it dialed in.

Similarly, it is crucial for ATVs with Keihin carburetors that you check the valve clearances, as they cause the same symptoms as those of Sportsman 500s with CV carbs. Inspect the secondary air intake port at the venturi – the small non-replaceable jet embedded in the passageway. Disassemble the carb, spray cleaner through the passage, and then take a small-diameter wire and run it through. Blow through with compressed air to complete your thorough cleaning and repeat from both directions of the valve clearance.

3. Camshaft & Exhaust Lobe

The exhaust lobe on the cam is prone to wear if you neglect scheduled oil changes. In extreme cases, the exhaust lobe is so worn-out that a rebuild is needed. Interestingly, the exhaust lobe wearing out on the camshaft is responsible for the restricted acceleration of the Polaris 500 90% of the time.

If the cam turns out to be the problem, you will need to replace the rocker arms. Also, remember that this troubleshooting step is only necessary if both the CDI and carburetor check out. It is also best performed by a professional as the timing procedures are meticulously done.

Other Things to Check if Your Polaris Sportsman 500 Dies When Accelerating

1. Fuel

Insufficient fuel may be a cause of your Polaris Sportsman dying when accelerating. If you suspect this, refill the gas tank and ensure that you turn the cycle key on at least three times before restarting the engine. Additionally, check that the fuel is not set to “reserve.”

While checking the fuel quantity, inspect that there are no clogged or damaged fuel vents impeding the flow of fluid and that the fuel itself is compatible with your ATV and not watered down. Drain and replace the fuel inside your gas tank if found to be incorrect.

2. Restricted Airflow

Limited airflow is another cause of ATV bogs when giving gas. Unlike the other symptoms, this is easier to pinpoint as the machine revs and idles just fine when you let off the gas, or your ATV will be running either too lean or too rich.

Usually, a dirty air filter or carburetor, stuck-on-close choke, plugged main jet, junk-filled float bowl, misadjusted valves, or air intake tube blockage is responsible for this restriction. Resolving any of these causes will vary depending on the year of your Polaris Sportsman 500.

3. Parts Malfunction

If your ATV bogs down when applying throttle, you likely have defective spark plug wires, non-working reverse speed limiter, electronic throttle control glitches, and sometimes even a bent rocker arm. A seasoned mechanic can opt to replace defective parts with OEM ones and resolve the issue themselves. Otherwise, these mechanical failures merit a visit to a Polaris dealer to administer repairs.

Identifying why your Polaris Sportsman 500 dies when accelerating can be tricky and should not be confused with other known issues for the quad. Some of these common problems include the vehicle not turning over, engine not starting, machine backfiring, stalling, misfiring, and the Sportsman overheating.

Always refer to your owner’s manual for guidance and step-by-step procedures on troubleshooting specific Polaris ATV issues.

4. Throttle Cable

Carbureted Polaris Sportsman 500 ATVs specifically have what you call an ETC or Electronic Throttle Control. The two metal contacts of this assembly should never touch. Otherwise, it will cause the machine to die. If you figure out that this is the cause of your quad stalling or dying during acceleration, you need a throttle cable adjustment.

When adjusting, make sure to route the throttle cable correctly along the channel found on the side of the gas tank. Check that the throttle channel is not kinked or obstructed in any way.

5. Cleanliness

Keeping your quad clean not only make it last longer, but it also helps with your vehicle’s proper function. In some instances, your Polaris Sportsman 500 dies when accelerating due to dirty spark plugs and debris in the fuel vents or the radiator, not because these parts are faulty.

Regular cleaning of your quad inside and out goes a long way in preserving how your wheeler operates. If certain parts are beyond filthy and cannot be salvaged via cleaning, it’s time to replace them.

EFI Loss of Spark

For fuel-injected Sportsman 500s, you need to check the map, crank, or TPS sensor harness wires to see if wiring pulled out from the sensor connectors causes the problem. These tiny sensors are bad at shorting out against the starter or engine case. They also do not need bare spots to be defective as their soft spots internally make them prone to issues.

You should also maintain fuel pressure at 39 psi. If you get lower or erratic pressure readings, then it could point to a fuel pump problem. These two checks are necessary on top of troubleshooting that you would normally do for a carbureted Polaris 500.

Polaris CDI Installation

This video demonstrates the proper installation of a Polaris stator and CDI ignition kit for a 1998 Polaris Sportsman 500.

How to install the CDI box:

  1. Remove the bracket (Torx T25).
  2. Disconnect the following plugs from the old CDI box:
    • 2 pins plug (pickup coil)
    • 3 pins plug (source coil)
    • Blue/white wire (ignition coil)
    • Black wire (kill switch)
    • Brown wire (ground)
  3. Connect the new DC CDI box to their corresponding plugs, as seen in the video.

The Polaris CDI kit is a plug-and-play unit that should connect to the same plugs that disconnect from the stock CDI (except for the orange wire, the hot switched wire). For DC conversion kits, this orange wire connects to the Polaris Sportsman 500 battery via a hot wire terminal where the box will draw power from instead of the stator.

The hot wire terminals on the ’98 model are located on either side of the two open terminals beside the switch top circuit. You can also crimp the bare end of the orange wire with a female spade tuner so you can press it into the junction board, tucking it neatly into place.

Installing a DC conversion upgrade kit is fairly straightforward. Choosing to upgrade to a DC ignition system is better than a conventional CDI box that requires a working source coil for two reasons:

  1. It will work even if your source coil is defective.
  2. Cold-starting will be easier.

For a ’98 Sportsman, you can mount your replacement CDI box on the crossbar in the engine compartment using a cable tie. Take note too that only an OEM Polaris CDI box replacement resolves the loss of power in certain cases.

Conclusion – Polaris Sportsman 500 Dies When Accelerating

Your Polaris Sportsman 500 dying out during acceleration can be frustrating, especially if you do not know why it occurs. The problem usually traces back to the CDI box, making cut-off throttle response easier to resolve and manage.

If the CDI box doesn’t need replacement, verify if you have spare parts that you can use to replace current ones. Regularly cleaning your carburetor and being on top of your scheduled oil change also do wonders for your quad. With restricted acceleration at bay, you can fully enjoy your Polaris Sportsman 500.