I have a Yamaha YLM 342 SR Lawn Mower and am trying to find out how to replace the clutch? I have adjusted the cable but the clutch is still slipping I think it is worn out.

could be dirt in the carby , blocked fuel filter or lack of adjustment in the accelerator cable
I will go for a cable adjustment as they slip under the clamp on the carby bracket when the throttle is pull wide open

It is slipping. These big yamahas normally have slipping clutches. Mine slips, I've just learned to baby the clutch. Make sure you are in the most comfortable gear for the speed you are running at. Avoid rolling on full power at low speeds in higher gears. It's the nature of these great beasts. Clutch springs are too weak in these bikes, you may consider an aftermarket clutch spring assembly. The "shudder"(intermittent slipping) is caused by glazing. Make sure you are using the right lubricants for your bike, some synthetics can cause problems.

1)Adjust clutch cable correctly, check
2)Pull the clutch assembly apart, if there is little wear then you have "glazed" plates, clean each plate with 600 grit sandpaper and reassemble...get a new clutch spring assembly (weakened spring causes "shudder", slippage, and consequently glazing). Reassemble and adjust correctly (many forums out there with info).
3)Replace the full assembly and adjust correctly at setup. Adjust regularly....I check adjustment about every 300-500 miles.
4)Pay a shop to do these things for you.

Did the cable break? Or did it just stop working? In general you have to figure if it came off, break or did the adjustment slip. Readjust if necessary or replace the hole cable or re install it correctly. Simple Question, so many answers. And if all else fails, take it to a lawn mower repair shop.

You have to adjust the tension on your belt, or if there is no adjustment you may need to replace the tension spring, or possibly the belt is worn to the point of excessive slipping.
GOOD LUCK.

This 1991-92 model is equipped with a blade brake clutch. When the blade slows down this means the belt is slipping. This slipping can be caused from a few different things.
1 --A loose cable.
Try adjusting the blade cable on the upper handle. this unit has an adjustable section. make sure the cable is not so tight that you snap it.
2 --A sticky pivot point under the belt cover
The belt cover in the back builds up with dirt and debris. Make sude it is clean under the cover and all of the pivots move freely. ( do this with the engine off)
3 --A sticky belt tensioner under the deck cover
The underside of this machine has a metal cover to protect the belts. Remove it and check that the blade belt idler arm is not frozen in place. this will cause the belt not to enguage all the way.
4 --A worn belt or belt pulley
The large flywheel and pulley can wear. Check this if the belt looks good.
This is all there is to the machine BBC system.
I hope this helps.

Get parts and more diagrams at a Master Toro Dealer like www.arcolawn.com

If you have such a manual for a Yamaha YLM 453 mower, I would like to have it please.

You can adjust it by slackening the cable...unless it has hydraulic operation....Otherwise get it replaced before you do more damage..ie clutch dust and debris in the oil, so dont forget the oil and filter change too.

sounds like you need a new clutch. but first make sure that your clutch cable is'nt too tight. it should have a little bit of freeplay when you pull the lever.

a common problem is behind the drive wheels there is a gear and pin system which can stick with age or amount of use,remove them taking care to note how they came of for rfitting,clean them and put a small coating of grease on them when you refitt and should cure problem,ther is no adjustment for the clutch,sometimes you need to adjust cable but some models had no adjustment so if cable stretches you have to replace them,hope this is of help