SOHC.co.uk Forums > CB350/400
Carbs off bike - Total disassembly or not?
Mikep328:
Well, I'll give it a try with the airbox mounted to the carbs first, maybe it'll work (or not)! In looking through my receipts again I found that it does have a new (reproduction) airbox from DSS in 2022.
Matt_Harrington:
I'm pretty certain you will need to fit the airbox after fitting the carbs. There is a technique which I found but it is still a fiddle. You should be able to access the airbox from where the air filter would be to push the central parts home. I used a very thin smear of red rubber grease to ease things along. As Ted says, without the air filter housing, its nice and easy!
McCabe-Thiele (Ted):
--- Quote from: Mikep328 on August 08, 2023, 05:57:21 PM ---Well, I'll give it a try with the airbox mounted to the carbs first, maybe it'll work (or not)! In looking through my receipts again I found that it does have a new (reproduction) airbox from DSS in 2022.
--- End quote ---
Pretty sure that will not work as there is not enough room if the air cleaner box is in place - it's a tight gap.
Mikep328:
To follow up...
I did not attempt to refit the carbs with the airbox attached. As has been stated, it didn't look possible at all so I did it the 'normal' way - airbox in place (more or less)/carbs slid in from the right side. I lubricated all the rubbers and from the time I started to slide the carbs in to the time they were in position on the manifold and the airbox rubbers attached was maybe 5 minutes! I've read about how difficult this can be so I figure I got lucky but I'm not complaining. As they say, luck is better than skill!
No leaks or other unpleasantness, bike started immediately (choke on). After warming up I adjusted the airscrews per the Honda instructions and went out for a ride. The huge bog was gone and the bike took the throttle quite well though I think further tweaking could smooth it out even more. I had bench synced the carbs and, TBH, I don't know if it's worth doing a vacuum sync since it runs very well. I'm very pleased, neat little bike!!!!
K2-K6:
Sounds like good progress and satisfaction in working through it yourself.
Carburettor synchronization, no difference between bench & gauge if carried out with careful diligence. Obviously easy to set them on bench when they're not fitted, once installed of course you'd not consider taking them out to do this, hence gauges to facilitate. Sync'ed is Sync'ed though either way, id not sweat it now, there's nothing magical in it as often expected on the great wide Internet view.
Sync hasn't the fine resolution to adjust and compensate for idle refinement anyway, thats always been through those idle circuit adjustment and optimisation to bring parity of burn for each cylinder with the main slides virtually closed.
This is mirrored in fuel injection system as follow on from carbs, the ecu monitors crankshaft pulse and bleeds different level of air into early systems to keep them stable with fairly crude injector control being insufficient.
Later, multipoint system more currently use crank monitors and trim cylinders with injector pulse length to keep them even. Same as these carb strategy wise, these just use you to monitor the crank rpm in trimming the mixture.
It's perfectly acceptable to have different carb to carb air screw settings as the cylinder burn takes precedent in smoothness, the screw adjustment just compensates for any variation in that carb, jet, cylinder compression, spark plu etc and gives you the means to get equal firing pulse energy to make it all smooth.
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