Slack chain.

[bogan]

I'll say. That'd be hella cheap for a chainsaw, let alone a motorbike...

you can get well cheap industrial chain, think the one on my electric was bout 30bucks, is as big as the one on my bros too! I'm running bout 5mm slack on it too

[Ixion]

Check your wheel bearings and swing arm bushes.

[MSTRS:Me]

New chain + worn sprockets =
maybe you know why, now?

[glegge]

Check your wheel bearings and swing arm bushes.

+1, also check the adjuster cam's or whatever you bike has, are working as they should to hold the wheel in the correct position.
in a nut shell, things that can effect chain tension.
gearbox output bearing
front sproket
swing arm bearings
chain itself (wearing quickly)
rear sproket
rear wheel bearings and chain carrier bearings (often seperate with rubber blocks between them for a smooth ride)
adjusters (the cam or nut and bolt arrangment that holds the rear axle and allows you to more it forward and back)
also - adjustment method. IE ensure you check before and after adjusting, also ensure after tighetning axle that the adjusters are snug.

[F5 Dave]

Industrial chain is meant for running low powered machinery at a constant speed. Not the abuse a bike with a constant gear changes & acceleration goes through. + as MSTRS sez the sprockets are worn to the old chain so will stretch teh chain to that point in fairly short order.

Jesus Christ mate...that's nasty! You'll tear the front countershaft out of a bike one day adjusting the chain that tightly! The tightest point for the chain...is when the swingarm is parallel to the ground!!! Adjust it with one of your mates sitting on the bike if you must...but NEVER over tighten it FFS.

Yeah that's one of the reasons I don't trust shop mechanics to work on my bikes, an ex's GS was particularly prone to that & it came back from 1st service with a chain like a bowstring when compressed.

[Crasherfromwayback]

Aye. Better too loose than too tight!

[MSTRS:Me]

Well, chains, anyway...