Topic: A few quick questions on a CB750

[flyin_]

So I finally got my 76 CB750 running and started to fine tune it. 
After a carb sync it is running much better but I can't get it to idle under about 1500 RPM and it seems to decrease engine speed slowly after reving the engine.  Other than that it seems to run pretty smooth and revs well.  I installed Keyster carb kits and I'm wondering if I should have kept some of the original metal in the carbs?  Does anyone have any experience in replacing with these kits and using some of the kit parts and some of the originals?

Under about 1500rpm it starts to chug and sound pretty rough.  There is also a clanking noise that gets pretty loud when the RPMs drop below 1500 or so.  This noise seems to deminish when the clutch is pulled in.  I think its either the clutch or the cam chain.  I would like some opinions on how loud this should be (cam and clutch).  I have not ridden a CB750 since I was a kid so I don't have much experience. 

by the way, I set the cam chain tensioner and the valve clearances according to the book.  I still need to verify that the cam chain tensioner is working properly and is not gummed up though.

Thanks for the input

[tramp]

idle on mine is about the same, they are cold blooded in the morning and can be noisey
at idle at any time sounds like clutch noise when you pull in the clutch
when i pull mine in the noise doesn't change much

[turnenwheels]

The idle on mine is about 1100rpm as well, As said very cold blooded.  once the rpms get up there after reving it does take a bit for it to come down...these bike are a trick to get the idle right on and syched in...carry a few tools around with you when you ride, cause when it gets warmed up you will need to change your adjustments for sure. 

[Zip]

You will also find that as you work on the bike over time you will become more familiar with its personality and what it want and needs.  I think the word for it is 'tinker' (not the negative connotation).'

Zip

[Gordon]

Did you adjust the timing, valves, and cam chain before synching the carbs? 

An exessively noisy clutch box at low rpm indicates carbs are still out of balance, but you need to do the aforementioned procedures first. 

[mrbreeze]

ditto that Gordon......the carb synch is the key but the basics must be there first!

[flyin_]

Thanks guys,
I have set the valves and points and synced the carbs.  I couldn't find a timing light so that will be done next week.  Hopfully fine tuning the timing and then re-sync the carbs will help.  (Does anyone know where to buy a timing light for under $50?)

How do I know that my cam chain adjuster is working?  Should I be able to stick a wire into the end of the tube and feel the chain after the bolt is loosened?  If for some reason my cam chain tensioner was not working, what kind of damage could I do if I ride the bike for a while? 

[Boomologist]

My chopper (CB750) developed a horrible rattle/clunking noise in the transmission area at an idle. It went away if the clutch was pulled in.  It was so bad that at a traffic light people would stare at it and wonder if they should run for cover.
I dismantled the engine thinking I would find broken gears, at least. Nothing!
Turns out that if one cylinder is mis-firing it will slam the transmission gears back and forth causing this noise.