SOHC.co.uk Forums > CB350/400
A couple of "tune up" questions...
Mikep328:
Yes, I typoed an extra "0" in my message. So for those that work on these engines regularly - that clearance (as stated in the manual), .05mm/.002" IS CORRECT? In handling that thickness feeler gauge, it seems like pretty much "no clearance!" :)
Trigger:
--- Quote from: Mikep328 on September 08, 2023, 08:19:37 AM ---Yes, I typoed an extra "0" in my message. So for those that work on these engines regularly - that clearance (as stated in the manual), .05mm/.002" IS CORRECT? In handling that thickness feeler gauge, it seems like pretty much "no clearance!" :)
--- End quote ---
It is correct in the manual. All the rest: 500, 550, 750 SOHC are 0.08mm on the exhaust and 0.05mm on the inlet ;)
K2-K6:
"The bike is running great overall and idles nicely at 1200 RPM but there is some roughness at constant slight throttle opening, as in slow town traffic where the throttle is at maybe 1500-1800 in low gear. This was very apparent/annoying in Bristol yesterday. >:( It also still does not take opening the throttle quickly as well as I think it should. I figure the mixture screws need more attention and/or my bench sync was not as good as I thought it was. ::)"
Try it with the idle circuit air adjustment screws moved in 1/8 to 1/4 from where they are now, this to make is slightly richer as it progresses along the idle circuit metering.
These "idle" circuit control the low speed mixture primarily, but also with significant impact on how the carbs get into mainjet operational range, too weak here will make it start to fall flat on it's face (going temporarily lean) as it tries to get a smooth increase onto fully running main jet. They are very accurate in the amount of shift needed to refine that relationship, but ultimately very smooth and linear when set correctly.
If you can't get them smooth within decent adjustment range, it's nearly always how clean the low speed air and fuel jets/holes/flow components are.
Absolutely scrupulously clean and they work impeccably, any impairment and you'll chase yourself round and round trying to get them to work well and without throttle glitches.
McCabe-Thiele (Ted):
--- Quote from: Mikep328 on September 08, 2023, 08:19:37 AM ---Yes, I typoed an extra "0" in my message. So for those that work on these engines regularly - that clearance (as stated in the manual), .05mm/.002" IS CORRECT? In handling that thickness feeler gauge, it seems like pretty much "no clearance!" :)
--- End quote ---
Compared to old push rod cars the valve clearances are imho relatively small. When I adjusted mine I used feeler strip and made sure that the strip was not pinched but just free to move when pulled. As usual tightening the lock nut would sometimes pinch the strip so I would back off the screw & start again. Worth getting it right for sure.
I do not know what work done on the carbs by yourself or the PO, as K2-K6 states they need to be ultra clean to run correctly prefferably using original brassware to run smoothly as well as the correct float levels. Clean fresh petrol & an intact strainer on the Petcock a must.
Mikep328:
I disassembled the carbs/cleaned all parts thoroughly. I reassembled with original brass, set the float levels, and installed new (NJ) Orings and bench-synced the carbs. On the bike with engine running each mixture screw functions properly, changing the idle as it is screwed in/out so I don't believe there is any issue with clogged passages, etc. I'll richen the mixture slightly, as suggested.
I'll check the tappet clearance/adjust if needed - it was allegedly set properly by the shop tech prior to my purchase... ;)
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