Hi armourbl,
I've got one of these and I use it as my daily ride. I bought it in bits after it was submerged in floods. It was cheap but needed lots of work and therefore the perfect bike to learn on. I'm no fool with a spanner but every bike has its quirks and these bikes are quirky! There is no way I could not have done it without the help of a few things.
Go to here www.cb750c.com and sign up.
Read this page first. http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&p=80601#80601 Its the new members page and you need to know it because they will bust your balls if your signature is not right or pics are too large etc.
Next and most important go here and get the workshop manual: http://www.cb750c.com/modules.php?name=Forums&file=viewforum&f=5 Mark sure you get all of it and all the addendum's. The addendum's have lots of info re your 1982 model.
This will educate you on the carbs: http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&t=9513 & http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf
After that read as many "sticky's" as you can. They are the bits of info that members have posted that are so well explained and valuable they are made a "sticky" by moderators.
Here is the specific valve info from the new members info page that will answer your question:
"Valves
Proper valve clearance is probably the most important maintenance issue to keep these motors running next to frequent oil changes and cam chain tension adjustments. Valve clearances need to be checked every 4000 miles or so. Most mechanics and long term owners of these bikes agree that the ideal valve clearance for these DOHC motors is .005" or .13 mm, regardless of what the book says. So, somewhere between .004" to .006" or .10 mm to .15 mm is acceptable. The book says .002" to .005" or .06 mm to .13 mm and those low numbers are just too tight and can lead to burnt valves.
The 25 mm diameter shims these motors use are commonly made from 2.3 mm to 3.5 mm in steps of .05 mm. On real Honda OEM shims, the decimal is left out, so what Honda calls a 280 shim is actually 2.8 mm thick. The in-between sizes with sizes that end in 2s and 8s like 272 and 278 were never sold over the parts counter and were only ever available in new Honda motors from the factory.
NEVER turn over the motor without shims in ALL the buckets! The cam lobe will bend up the bucket and the valve will stick open, and possibly hit the opposing valve and then you can have bent valves. Lobe damage can also occur."
And to answer some of your questions:
Those grooves on the end of your cams are not there as marks for adjustment. You will see in the WSM there are other markings. There is one groove/cut out that is used to identify where the cams need to be to check the valve shim gap, but you can read all about that in the WSM (chapter 3)
There is only one way to put these cams in. there is no adjustment. its either right or wrong and if it is even just one tooth out the bike will run like s$!t and may even bend valves. There is very little clearance when at TDC.
My experience pulling apart 5 different cb750/cb900 DOHC motors is the yellow markings are factory markings.
I have all my valve clearances at the .12mm to .15mm (you can do the math) Even if it is a bit noisier the risk of burning a valve is reduced. The valves only cool when they are in contact with the seat, therefore the lager the gap, the longer the contact and greater the transfer of heat from the valves. After doing this there was no noticeable difference in noise but the bike ran WAY WAY BETTER. And this is why: Compression increased!
My final piece/s of advice for you to become a better friend/mechanic to your bike BEFORE you work on it, is read the manual, then check if there is sticky. If there is a problem or you are concerned about something try to diagnose it or at least identify with some certainty what needs to be done. Then you are ready to take to it with a spanner. Thinking the cams (or any major component) is installed incorrectly on a bike that "runs good" is an over enthusiastic lack of knowledge, but hopefully that enthusiasm will drive you to get things done the right way with the above info in hand.
For a bike that is running well you shouldn't need much other than chapter 3 (Inspection & Adjustment) of the WSM.
Good luck. I am happy to help if I can, just ask.
