SFO; I will try to confuse him a bit more, but I am afraid he might have the RFVC motor (two carbs). I am not sure they will adjust the same.
Maxkixs; look for the adjuster right where SFO says it is. It is a big nut (14 mm wrench) with a rubber cover over it. If the rubber cover is gone, there will be a small 6mm (10mm wrench) bolt screwed down into the top of it.
In a perfect world, if you were to loosen the adjuster nut (the 14mm one) the aforementioned spring will pop the adjuster up to tighten the chain. As SFO has indicated, it rarely works that way, and is a little scary if performed on a idling engine, as if the chain is worn badly, it could jump. I like to help the adjuster to assure this doesn't happen.
Most often, the adjuster will need some help. This help can come from a bicycle spoke. I have no idea what size to call it, but there is a small bicycle spoke that will thread down into the guts of the adjuster. To use it, remove the rubber cap and remove the 6mm (ten mm wrench) bolt from the top of the adjuster.
The spoke will screw down into the guts of the adjuster and give you something to pull up on to help it do it's job. Make sure it is the right size, it need to grab good and not pull out of the threads.
With the engine idling and the spoke screwed into the adjuster guts; loosen the big nut, but this time you can manualy pull up on the adjuster (spoke) to be sure you are getting all the adjustment.
I NEVER attempt to adjust a chain in a running motor unless I have the spoke in my hand. Actually, I would grab the spoke with Vise-Grips to keep it under control.
If you clamp the Vise-Grips on the spoke at the point where it exits the adjuster, the adjuster cannot move down (loosen) and you are pretty safe doing this with the engine idling.
I like to have the engine idling so I can hear what I am doing.
I have never actually had a chain jump during this procedure, but be warned; it COULD happen. :eek:
Be careful, you can actually overtighten the chain if you haul on the spoke too hard.