SOHC.co.uk Forums > CB350/400
Carb sync
K2-K6:
As I was writing the above posts I was wondering the same thing. I can remember reading that method and was wondering just what happened at the factory during manufacture as I can't imagine the production line having to do a carb balance with gauges as a routine.
Well spotted about the paint though Julie. I guess you'd have to get knowledge about how Keihin set them up, which would seem like either drop the slides and mechanisms in then just lock the adjusters off. Or would they have run them on something like a flow bench that had a tapered four gang rubber socket to just push the carbs into and pull a vac through them to test and set parity.
Thing is, I've always in the past looked at them the way the manual says to and never really questioned it. But then I read that 5000rpm thing about a year ago and wondered if that was right. Puzzled over it abit (Yeh I know, a bit slow thinking time) and gradually realised what he was saying, and why.
Whatever the case, I think it's correct to set the carb's slides, as best you can, without the engine influence and leave them alone. The adjusters for the slides seem to imply this as you can only set them at one point for the whole range. There is no facility to alter them for progression over the range of use. You are just reliant on the production accuracy of the manufactured parts.
If you go for a moment to running an engine on miss-matched throttle slides, it's likely you'd get some differences in wear longer term from effectively running a different mixture through each cylinder.
I fully understand the view that there are manufacturing tolerances, but let's face it, the more you look at these four cylinder Honda's the more you have to be impressed at the original production line manufacturing capability considering what else was being produced.
Sometimes when you stand next to someone's bike, you can just here how well it's setup. It'll be interesting to see what royhall thinks by trying it. Sometimes people tell you little things that previously you've not considered, but some of them, just sometimes, can make such a difference.
Nurse Julie:
Interesting. I am no expert at carbs of any type but having had many bikes over the last 38 years with 1,2,3 and 4 carbs, I have always found the best way to get them performing ok is bench sync, make sure the floats are at correct height, there is no crud in them, put them on the bike and then just fiddle with the mixture screws. It may be considered a very basic and naive way of getting the job done but it works for me. Ultimately, it's usually us taking the carbs off the bikes for whatever reason, that messes them up in the first place. I have found generally but not always admittedly, that once the carbs are on and i have done the basics, they never need touching again unless a float holes or something gets blocked.
kevski:
Every thing is was made on CNC's where every cutting tool is only used for a pre-determined amount of times minimizing the amount of difference between component sizes, all put together in the same way with the same settings, then one is tested out of so many to check it works within spec, and so on and so on, the machines then end up in dealerships where the final assembly takes place then run up before being sold any out of spec issues are then dealt with, the 3hg range is quite wide but acceptable, my 350 come to me with 5033 miles on with the yellow marks still on the carbs, i renewed the rubber components in and around the carbs, also valve clearances, points and timing, fired it up and it was showing about 2hg difference on number one, within parameters i tweaked it a bit to give me around 1hg, CNC machining using best practice is wonderful but as of yet not perfect.
Nurse Julie:
I bow down to you experts knowledge but you are analysing the outcome of a minute difference of hg, what's the point?. If the bike runs, great. In my line of work if i got so hung up on a small variation on the human body, a majority of my patients would be in intensive care on life support just because their blood pressure was up a bit. If something works ok, live with it and enjoy it.
royhall:
Thats us told then. ;D ;D Problem is Julie, the 350F is a patient on the operating table again as I just rebuilt the carbs a second time (the way I should have done in the first place) and I am trying to learn from the experts the best way to set them up. Believe me, when the bike runs right I shall never touch the carbs again, I hate the bl***y things. :'(
I'm with you on that one though, if its running good leave it the hell alone.
The 350 is trying its best to die though. Whilst I was doing the carbs the battery decided instant death was the way forward. Never seen a battery go that quick ever, hence my other thread about batteries.
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