Vacuum synced carbs on my CB750 K1 last night and idle is smoother and clutch rattle less pronounced but still present. Top end was recently rebuilt when bike was restored. Stock pistons, wear within spec, hone, new rings, head ported, valves deshrouded, chambers polished, new valve guides, and new exhaust valves. Runs well and pulls strong. When syncing 1 and 2 were pretty much spot on, 4 was very close and 3 was a bit out. Bench sync was done with 1/8" drill bit. I think this is as smooth as the idle is gonna get at 1000 RPM. It'll stay running down to 400-500 RPM where it'll eventually stall if that low.
This is readings at my 1000 RPM idle. Needles have slight bounce but are moving in the same slight arc.
How much clutch rattle was normal when these were new? It would be nice to get it quieted down some more if possible but all my CB750s have rattled so it's obviously not a deal breaker for me. I'm wondering how common slop in the clutch hub damper rubbers is and if I should be opening that up to try to shim them. Also if the Goldwing spring steel mod is worthwhile? Does it reduce the holding ability of the clutch?
My main issue is clutch drag. Makes it hard to find neutral. I'm used to dealing with it and hit neutral before coming to a stop or if not blip throttle and it pops in without too much fuss. I'd love for the clutch to just work, fully release with no drag. I've used Valvoline 10w40 motorcycle oil, regular 10w40 car oil, and just changed to Valvoline 20w50 motorcycle oil. Everything seemed more or less the same with cheap car oil (forget brand) but maybe shifting a little stiffer than the 10w40 Valvoline bike oil. With the 20w50 there is more drag when cold and although I've only been on one short ride with it the shifting seems less stiff/notchy and maybe slightly less drag when hot than the other oils.
Clutch is adjusted properly and set for as much release as possible with a bit of free play at the end of travel. Clutch steels and frictions are whatever was in it when I got it they seem flat and measure well within spec. Inner basket is drilled extra holes as per the oiling mod. Countershaft oiler has new oring, oil pump is the best of 3 and has new orings and shaft seal.
In video clutch is pulled at about 20 seconds and around 1:20 where the rattle is less loud. What do you guys think of clutch rattle and overall engine noise?
https://www.youtube.com/watch?v=7TVdVgHXE4cAlthough there's a lot of opinions and experiences with different oils I'm not convinced any oil will make drastic changes or completely cure these issues. I may end up trying either Mobil1 diesel 15w40 or Rotella T6 15w40 as that's what I use in my truck and several here use it with good results. Would simplify things as it's one less different oil to buy when maintaining the fleet. Anyhow, I'm thinking it's a mechanical issue, and I'd hope at this point it's not insufficient oil after all the work to the oiling system.
Is replacing the steels and disks the next step? What brand is good? Don't want any drag, and once no more drag I'd prefer rattle to be as quiet as possible. Anything else to try?
