Skip to content Skip to navigation Skip to footer

Engine Bog Troubleshooting

The best solution to any engine problems is to visit your local Polaris Dealer. Find a Polaris Dealer near you with the Dealer Locator. But if you’re experiencing engine bogging in your fuel-injected snowmobile, including those with a model year 2019 850 Patriot engine, try these troubleshooting techniques.

1. Verify that any accessories — including aftermarket exhaust systems and silencers — are removed. Reinstall any stock components that were removed and replaced with aftermarket products. Then test ride your snowmobile. This will help determine if those components were causing the concern.

2. Make sure you’re using the recommended spark plug, which is the NGK BPR9ES for all 600, 650, 800 and 850 models since 2009. It is Polaris part number 3022082. Using other spark plugs and/or a non-projected tip can cause runability concerns.

Spark plug

3. Know that the ignition system is sequential. This means the MAG and PTO spark plug leads and caps must be on the correct spark plug. There are MAG and PTO bands on the spark plug wires. The MAG is the recoil side, which is the right-hand side if you’re sitting on the snowmobile. The PTO is the clutch side or left side.

4. Make sure the fuel injector break-in time has expired. The fuel injector break-in lasts for 2 hours, and the timer only counts down when the engine RPM is 5,500 or higher. Reference the engine hour meter on your instrument cluster to view total engine hours.

5. Check the type of fuel in the tank. Polaris recommends the use of 91 octane fuel or higher with no ethanol. Although 87 octane fuel is usable, some engine performance will be lost and fuel economy will decrease. Do not use lower than 87 octane fuel and do not use fuel containing more than 10 percent ethanol. Never use E85 or 88 E 15 fuel.

Operating with obstructed fuel systems will result in serious engine damage. Perform maintenance as recommended. Prolonged exposure to petroleum-based products may damage paint. Always protect painted surfaces when handling fuel.

6. Verify the fuel selector setting is set for the type of fuel in the fuel tank. Test ride the vehicle. If the concern does not get better, try the other fuel selector setting and ride in that mode for a while. This will help determine which mode exhibits the concern on your snowmobile.

When using the recommended 91 non-ethanol fuel, always select the 91 NON-ETHANOL setting. When using ethanol, MTBE or other forms of oxygenated gasoline, the fuel type must be changed to NON-PREMIUM/ETHANOL in the gauge. If you unsure of your fuel purchase, use the NON-PREMIUM/ETHANOL mode.

For more on changing the fuel selector setting, read Snowmobile Fuel Type Selection.

7. Verify the drive belt deflection is no more than 1.25 inches. Tight belt deflection is essential in allowing the CVT system to run in the right gear ratios. Belt deflection that is too loose will cause RPM bogging and hesitation.

Measure the belt deflection with both clutches at rest and in their full neutral position. Place a straight edge (1) on the belt and apply downward pressure while measuring at point (2). This measurement should be 1.25 inches (3.2 cm).

Belt deflection

To adjust the drive belt, do the following:

  • Loosen the driven clutch set screw with a 7/16-inch wrench. The set screw is pictured below. 

    Set screw
  • Using an 1/8-inch Allen wrench, adjust the set screw until belt deflection meets specification.
  • Holding the set screw with the Allen wrench, lightly tighten nut.
  • Using the L wrench, open the driven clutch sheaves 1/2 inch.
  • Tighten the deflection screw nut to 145 in-lbs.
  • Rotate the belt clockwise while removing the L wrench.

If you’re unsure how to measure or adjust belt deflection, see your Polaris Dealer.

8. Verify the correct drive clutch weights and springs are installed for your riding areas. The snowmobile should be clutched appropriately for the elevation you’re riding at. If you’re unsure, see your Polaris Dealer. If you have added aftermarket clutching, remove those and test ride the vehicle to determine if they were the cause of the problem.

For more information and maintenance procedures for your specific snowmobile, consult your Owner's Manual.
For more information, see your authorized Polaris Dealer. To find a dealer near you, use the Dealer Locator.
To find diagrams and replacement part numbers, use the online parts catalog.

Unless noted, trademarks are the property of Polaris Industries Inc.
© 2022 Polaris Inc

Keyword(s) engine , bog , rpm , 850 ,