I modified my atv last week. I put in an A12 camshaft, ported the head, 12g sliders, 1500rpm contra spring. Now it makes a loud click sound when under a heavy load. It does this on hill climbs and sometimes under full throttle acceleration. It feels like a gear slipping a tooth. While holding the front brake and spinning tires in gravel, the tire momentarily stop when it clicks.

There is a noticeable increase in low and mid range power over stock. The clutch is still stock. Could the increase in power be too much for the stock clutch? What would that feel or sound like? There are no weird sounds when moving under modest throttle opening.

 

Is your chain jumping a tooth under load?

 

I don't think the chain is slipping. I have it adjusted to about an inch to an inch and a quarter movement mid-span. The atv has maybe a dozen hours on it so the sprockets still look new.

I pulled the CVT cover off last night and found the clutch bell polished to a mirror finish with a few of might be chatter marks. There were dark lines in several spots on the bell. I sanded the surface with some 120 grit sandpaper and reassembled everything. Maybe it will perform better next ride.

 

Unless you have a broken spring in the clutch, I doubt you'd hear a clunking noise there. Were all the clutch arms firm? An inch or more of play in the chain is more than enough. I usually stick to about 1/2 inch. Plus, it's hard to say what flexes while the motor is under heavy load.

 

I assume this is a GY6 engine. Do you have a FNR gear box on the output shaft? If so make sure the cable/lever adjustment isn't leaving the gear box only partially in [F]orward. If it isn't fully engaged the gears try to climb apart and jam under load.

On my GY6 this caused severe lurching and bad sounds under full acceleration or hill climbing. The engine would speed up as the CVT geared down to try to overcome the mis-meshed gearing. A simple adjustment cleared it all up.

This was all happening when my quad was new. After adjusting the gear box, plus 4 years later, it is still working great.

 

I didn't notice any of the clutch arm being loose, but did not pull on them. If the spring was broken, the arm would swing loosely wouldn't it?

It is a gy6. The transmission is integrated into the engine. The shift linkage mounts directly to the engine. I haven't checked the linkage to see if it is out of adjustment. That is a great idea. I hadn't thought of that yet. Thanks

I should be able to get out again in the next couple days to see if it works any better.

 

I checked the shift linkage and both F and R engage the same distance from N while rocking the atv back and forth (engine not running) so I did not adjust it. I did find part of the issue when I pulled the carb to rejet it. The throttle cable bracket and ferrule were hitting the frame. When I replaced the carb, I made sure it had more clearance. No more clunking

I think there was less slippage on the last ride. No way to tell if it is the belt or clutch. It's not too bad so I'm just going to live with it now that it doesn't sound destructive anymore. If it gets worse then I'll start to worry and get a 2000 rpm contra spring.