SOHC.co.uk Forums > CB350/400
More carb troubles, engine won't return to idle revs
Nurse Julie:
--- Quote from: billdn on November 28, 2022, 10:22:44 AM ---So carbs ultra sonic cleaned and all jet holes clear and reassembly about to begin along with new o rings etc.
A question has been put to me by a friend that after bench syncing I'd still need to balance carbs, the impression I gleaned from BryanJ etc al was that a good bench sync should be near enough. Is my failure to do carb syncing after causing my problem of not returning to idle?
Haven't got that far yet but maybe why.
--- End quote ---
No Bill, if you have bench synced them and all the slides close when the idle screw is backed off, that is always close enough to get the bike running very well. We rarely even have to vac sync carbs after rebuild and bench sync.
Oddjob:
The cause of the problem, No.
I always vac sync carbs after a rebuild, a bench sync is fine for getting the bike running but a vac sync is the difference between "This is how they should work and this is how they do work".
If you haven't got a set of gauges then that's ok, just trust in your work, if you have got a set or access to a set what harm can it do, it's reassurance if nothing else. If you put the gauges on and you don't need to touch the carbs then it's a nice feeling that you've done a good job in the first place.
Every multi cylinder bike I ever serviced always had the gauges thrown on just to check everything was working as it should, even bikes coming in for their first 500 mile service were vac gauged, it was surprising how many needed altering to get them balanced as they should be.
billdn:
Cheers Julie and Oddjob, that's put that idea to bed finally. .
Bryanj:
The big thing is vac sync is the LAST thing to do in the service, customers would get upset when refused to "just sync" the cards without checking tappets, point gap, timing and cam chain
Laverdaroo:
I had that at a bike shop I was service manager at in Farnborough, folk would just come in for a sync and baulk when we said we would only do it all not just the sync.
We mainly did new stuff but quite a few mid 70's Honda's and Suzies used us but some were a bit put out. It's not like we didn't explain, they knew best. There was realistically minimal risk to them but for them to moan when just a sync was done that it was still ropey put stress on my workshop time and productivity as we'd inevitablby have to put it right FOC after they kicked up to the GM. The risk was always ours.
Perhaps they didnt like young upstarts (38 at the time!) explaining an engine to them they'd owned for 25 years and how one process can effect the other in the service etc. On the other hand, we had some super clients that just came in, handed the keys over and said, " work your magic on that, she's just a bit under the weather and needs a tickle". They knew the bill woud be the wrong side of £100, but knew that their bike woud be cock on when it left.
We liked those customers ;) :D
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