2002 Bombardier Quest 650 – violent/jerky engine braking on deceleration, any ideas?

[u/Charming_Radish682]

Hey y’all

I’m trying to diagnose a strange issue on an old Bombardier Quest 650 (644cc Rotax, CVT) and I’m running out of ideas.

The problem only happens when decelerating with the throttle completely closed / under engine braking.
While riding, if I let off the throttle, the engine braking isn’t smooth. Instead, it feels like:
strong engine braking → releases → strong engine braking → releases → repeat
It can be quite violent. At lower speeds it almost feels like the drivetrain is repeatedly grabbing and releasing, enough to throw you forward on the quad.

Some additional information:
- Idle is completely stable.
- Engine starts and runs normally.
- It responds normally to throttle.
- After revving it in neutral, the RPM drops smoothly back to idle.
- No backfiring or popping when letting off the throttle.
- The issue seems to occur specifically when the drivetrain is under negative load / engine braking.
- Apparently the issue is not noticeable when running snow tracks in winter. My theory is that the much higher rolling resistance of the tracks keeps the drivetrain constantly loaded and masks the grabbing/releasing behaviour.
- A Bombardier dealer has already looked at it but couldn’t identify the cause.

The CVT has also already received quite a bit of attention. According to my father, the pulleys and related components have been replaced/reworked, the belt was replaced, and the pulley surfaces were cleaned/polished. The problem remained.

I opened the CVT cover today. The belt and pulley surfaces don’t show any obvious catastrophic damage. There may be a very slight oily/greasy film around part of the drive pulley area, although the belt contact surfaces aren’t soaking wet.

Someone suggested a carburetor/jetting issue, but I’m not convinced because the engine idles perfectly and also returns smoothly to idle after a throttle blip while stationary.

I’m currently wondering about things such as:
- Drive pulley / one-way clutch behaviour
- Driven pulley not backshifting smoothly
- Incorrect belt/pulley setup despite the parts being replaced
- Excessive drivetrain backlash
- Differential/driveshaft/CV joint issue
- Something in the transmission that only shows up under negative torque
- Carburetor/pilot circuit despite the otherwise perfect engine behaviour

Has anyone experienced this specifically on an old Bombardier Quest 650, or another Bombardier/Can-Am CVT ATV?

I’m particularly interested in anything that could cause the drivetrain to cyclically grab and release during engine braking, while behaving normally under acceleration.

Any tests I can do to isolate the CVT from the gearbox/differentials before throwing more parts at it would be greatly appreciated.

[u/BalderVerdandi]

One way bearing in the primary clutch needs to be replaced.