Chain too tight or too loose.

[moto]

In the owners manual it says to measure the drivechain slack while the bike is in the straight up position with no weight on it.
Slack should be 30-40mm.

At the moment it is 60 mm but if I loosen the axle nut and brake caliper bolt and move the adjusting plates one more notch each side the slack is only 20mm.
I think when I sit on the bike the chain will tighten some more and be too tight.

Out of the 2 options which is the best.

[Blue_SV650S]

I presume you have a cam adjuster like this? ...

https://www.trialendurodirect.com/images/products/product_info/yoomee%20cams.JPG

... hence can't get the granularity you are after?

Anyway, yes the best way to do it is to put all your weight on the bike, if you can get the swingarm horizontal then this is the tightest point, if there is still some play there, you are good to go.

Oh and when checking for tension, always roll the bike forward a bit and check again, tight spots in the chain will give differing readings!
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The purpose of life is to fight maturity.

[TUG]

You need to adjust your chain correctley, which would be on the chains tight spot. Keep turning the wheel and adjusting it equally untill you can find the point where your chain becomes tight but else where slacker. adjust to 30-40mm.
If at the tight spot it can be lifted off the back sprocket then your chain is fubar and possibly your sprockets if spikey.
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Haz ER-5, innit!

[moto]

Yes I have a cam adjuster either side of the axle like in your picture.

Sprockets are brand new.

I can get either 60mm or 20mm slack.

[neil.]

IMO if you are absolutely sure there's no way to get the perscribed amount of slack, then I would say it's better to be a bit too loose rather than too tight. Too loose means the chain might come off the sprockets or jump teeth, too tight means you are stressing the output shaft bearings on the engine.
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CBT February 2008 | A2 June 2008 | Yamaha YBR125 (written off) | Honda CBF125 (current)

[random_rob]

put a bigger chain on, or take some links out.
then you might be able to tie either a longer or shorter chain in with the adjustment on the bike.

[TUG]

If the sprockets are brand new, is the chain?
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Haz ER-5, innit!

[Gazdaman]

IMO, chain tension should always be tested with you sat on the bike.

20mm is slightly too tight, but if that's with you sat on the bike, I'd probably go with that rather than 60mm.

Although generally I would say slightly too slack is better than slightly too tight.

Gaz