Chain has some slack. Is this normal and how tight should it be?

Slack is necessary to prevent early failure of the bearings on the wheels. It is also necessary for proper operation when the oven heats up. slack shouldn't be too much or the chain may fall off the teeth. Too tight and you have wear. The abrupt stopping indicates the need for lubrication of the motor.

Could be it's too tight.
There is supposed to be some slack in the chain.

Any time a chain comes off it means there's slack in it or something's not tight enough. Not looking at your bike, I would have to guess that you need to loosen the bolts on the back wheels and then pull the wheel assemblies back until the chain is tight. This is probably a two person job, one to unbolt and bolt and one to apply tension. That being said, many years ago I remember bikes my friends used had a problem where if they were riding at a good speed and then stopped peddling to coast, then slightly reversed peddling, then started fast peddling again, that they would throw a chain. I think what was happening was they were creating slack in the chain by coasting, slightly reversing their peddling, then starting again. The chains were also slightly gummed up, allowing slack at this time.

3/4-1 inch slack up and down total movement at center of chain run. After adjustment rotate chain and check for tight spots, if the chain is stretched it must be replaced and the drive sprockets checked for exce

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ssive wear.

Provided you have not been in an accident that has bent your frame,upper and lower triple tree, or forks, the only alignment you can make is to adjust your chain. If the the front wheel is not tracking with the back wheel you just have an improperly adjusted chain. On each side of the swing arm by the rear axle are two chain adjuster cam/wheels. The have numbered bump/stops. Both chain adjusters should be set in the same numbered bump/stop to align the front and rear chain sprockets and the front and rear wheel tracking. the adjusters are on the machine for the purpose of setting the amount of chain slack. Your chain should not be too tight or too loose. If you grab your chain in the middle and push it up and down, you should have a slack measurement of 1 1/4 inches from the bottom edge of the chain to the top edge of the chain. If the setting is off the best way to make the adjustment is to raise the rear wheel off of the ground. A race bike stand is very helpful for this and oiling and caring for your chain. Harbor freight tools sells a cheap rear stand for about $35 (buy the cheaper one piece non-collapseable stand). Pull out the cotter pin, loosen the axle bolt, turn both adjusters till you have the correct amount of slack and they are both set to the same number. Tighten the axle and recheck the slack. If you notice when spinning the rear wheel that the chain goes tight then slack, you have a stretched section of chain. If this is the case you should replace the chain and any worn sprockets at this time.

What kind of motorcycle? Dirtbikes require more slack than streetbikes. Normal streetbike operation requires 1/4" up and down for a total of 1/2" from its highest point lifted to its lowest point pushed down. Offroad requires slightly more. This does not have to be exact but for rule of thumb, slightly loose is better than too tight. Hope this helps.

The cam chain tensioner is an automatic device. When the chain wears past a certain point and the tensioner can no longer compensate for the slack, it must be replaced.
Failure to replace a slack / worn chain can have severe consequenses, even if the chain does not break.

The first step is to find the tightest part of the chain. Unless it's a brand new chain it will have a tight spot somewhere on it. It's easiest to do this with the bike on a race stand if you have it. Rotate the wheel and observe the lower part of the chain and watch it lift up when you hit tight spots. The spot where the chain lifts highest is the tightest part of the chain. Once you have found this spot, grab the chain on the low side under the swingarm and move it up and down. It should move up and down around 30-35mm or so, or an inch and a bit if you're an imperialist :) If the chain moves more or less than this then it needs to be adjusted.

To adjust the chain, you need to loosen the axle first. Don't take the nut off but it has to be loose enough to undo by hand. Using 2 spanners, unlock the lock nuts on the end of the swingarm and wind the nut in or out until you get the correct amount of chain slack. always do the sprocket side (left side) first, then repeat the same on the other side. Check the chain adjuster marks to make sure that the adjusters are equal on both sides, this will make sure your rear wheel is aligned properly.

Once you have adjusted the chain, tighten the rear axle and check again. The chain slack will change slightly after you tighten the axle, it might go tighter, it might go looser. Depends on the bike. But the chain slack must be correct with the axle tightened. A bit of practise here and you will be able to guess the correct amount before tightening the rear axle.

Once you have the slack set correctly and the axle is tight, make sure to tighten the adjusters. Tighten the front nut first against the swingarm plate so it can't move. Do it tight but not crazy tight. Then holding the first nut so it can't move tighten the locknut against the first nut. Repeat this on both sides.

If you are not quite sure if the chain is right, always err on the side of making it too loose rather than too tight. Running your chain too tight can destroy your output shaft bearing. It's only about $30 or so for a new one but your engine needs to be completely stripped down to replace it, it's not a fun job. I have seen a lot of FZs and FZRs have this problem because people ran chains too tight. If your chain really is too loose then it will start making your gear changes harder to do, that's the sign you need to tighten it.

Look at the rear axle. There should be marks on both sides indicating where the axle is in relation to the swingarm. Note the position of the axle, then loosen the axle. There MAY be chain adjusters at the back end of the swingarm, but not all bikes have those. If yours does, as you look at the swingarm from the rear of the bike you will see two adjustment bolts. Tighten those up, and make sure you keep the axle position indicators the same on both sides. Your chain should have 1-2 inches of slack as you lift and press down on the middle of the longest run of the chain. Often there is a sticker on the swingarm that tells you how much slack is acceptable, do as the sticker says if it is there.

40mm slack up and down middle of chain. not tight when sitting on bike. loosen axle ajust both sides evenly, retighten axle install new split pin