My son's go kart (Yerf Dog) slipped the chain. You tighten by sliding the engine back, which I did. Now the clutch slips. Worked fine before.
Any ideas? (I tried dry wiping down the plates.)
Two pics and a video if you want to see the (in)action in process. Sad 10 year old was supposed to go riding tomorrow.
TIA for any help.

Looks like the drive side is just a bit crooked from when you loosened it up & then retightened? And/or a bit too loose. Plus maybe the belt got worn & is not engaging fully like it should, compounded by not being exactly square, which is important.

Looking at the video again, is there a key on the shaft on the driven side, that could be where it's slipping.

(I do see a keyway on the driven shaft. Something to check.)

Try a different belt size.

The 6 bolts you loosen to slide the engine back are in a 'channel' so there's no way to move it left/right only front/back. (pic below)
The reason I don't suspect belt wear is because it worked fine before it slipped the chain.
Not sure I follow what you are saying about a 'key on the shaft'? Thanks.

I don't know nuffin' about go karts but ...

If the chain is too tight there might be enough added resistance to cause the belt to slip. Make sure it's free wheeling and check the chain sprockets to see if they're properly aligned. I see a sprocket adjustment on the axle shaft.

Some coarse sandpaper will remove any glazing on the belt if that's a concern.

I see the slots the bolts go through, but I don't really mean sliding it far left, to right. More like the slop in the tolerance allows the motor to be slightly cocked, if the motor is not held straight when tightening. It looks just a bit off.

The keyway is the little slot in the big shaft of the driven clutch in the second picture in the first post. The key keeps the clutch from spinning on that shaft. You would have to remove the driven (big) clutch from that shaft to check it. Something made the chain come off, likely a hard hit, or something got in a severe bind. Chain/sprocket is rusty & could use a bit of lube, too. (A little goes a long way.) Friction there could cause it to jump, too.

Just troubleshooting from what I can see. No offense intended.

How many times have you had to move the motor to take up slack in the chain? Kinda sounds like moving the engine back to snug up the chain has made it so that the clutches on the belt drive aren't able to get any more grip. Have you considered just taking a link out of the chain? Easy to do.

This

....put the engine back to where the clutch WORKS,....than adjust chain tension by subtracting links,than maybe adding a half link.

Belt is WAY too loose, as pictured

Luck.

GTC

Looks like the rear pulley is slipping, As oulufinn said it may have lost the shaft key.