Author Topic: 74 cb 550.... Another carb question.. Rebuild kit from ebay (updatedx2!!)  (Read 5233 times)

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Offline TwoTired

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Re: 74 cb 550.... Another carb question.. # of turns for these screws (UPDATED)
« Reply #25 on: December 20, 2013, 11:57:48 PM »
The shop manual is pretty clear that the air screws are turned outward from lightly seated 1 1/2 turn, +/- 3/8 turn, at least for a bike with all stock components.
What were they set at before taking it all apart?

Is there some other problem that you need help with?
« Last Edit: December 20, 2013, 11:59:29 PM by TwoTired »
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

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Offline Honda550k

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Re: 74 cb 550.... Another carb question.. # of turns for these screws (UPDATED)
« Reply #26 on: December 21, 2013, 12:03:46 AM »
Hey jimsun

Picture number 2 are what I believe are air mixture screws. The stock setting for those from a gently closed position is 1 1/2 turns out +- 3/8 . For you to know if it is a plus or minus from the 1 1/2 turn, you'd have to get it running again. Do the 3 k tune up and sync the carbs with the 1 1/2 turn setting. Then play with the 3/8 you have for adjustment and see which position idles your bike the best at 1000 rpm and throttle feel. All trial and error.

Note: the more you turn them out the more air is in the mix which will make it leaner. Counter is + clockwise is -.

Resource:
http://forums.sohc4.net/index.php?topic=8986.0

Reply number 2

Thanks to TT

* Someone chime in if I'm wrong. I'm trying to relate this with my 78 550. I have air screws but those are IMS which only deals with idle.

Offline dave500

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Re: 74 cb 550.... Another carb question.. # of turns for these screws (UPDATED)
« Reply #27 on: December 21, 2013, 01:16:32 AM »
dont worry about the turn count its how it runs,unlike most automobile carbs these ones idle mixture adds to the entire mixture even into the high rpms,it doesnt just affect the idle!car type carbs idle circuits shut down once the rpm picks up,car type carbs have more circuits than these type one carbs,our carbs dont have a power/economy circuit or accelerator pump,tune and set up these carbs once the engine is fully hot(and with perfect ignition settings) and how it behaves when dead cold so be it,learn to feather the throttle or use that screw underneath the throttle if you have it to hold a fast cold idle,the book specs of so many turns out is a ball park,a bit like bench sync,you may find you need more or less turns by some degree more than the listed specs,dont let that worry you so long as the engine is running as you want,for example my 550 engine with 38/100 jets and 4-1 pipe and stock induction air box has over two turns out on the solid type idle screws,itll pull away from 2500 in top gear ok.
« Last Edit: December 21, 2013, 01:18:57 AM by dave500 »

Offline Deltarider

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Re: 74 cb 550.... Another carb question.. # of turns for these screws (UPDATED)
« Reply #28 on: December 21, 2013, 01:26:14 AM »
Quote
,unlike most automobile carbs these ones idle mixture adds to the entire mixture even into the high rpms,it doesnt just affect the idle!
That's my experience too (stock CB500).
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Offline dave500

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Re: 74 cb 550.... Another carb question.. # of turns for these screws (UPDATED)
« Reply #29 on: December 21, 2013, 02:24:58 AM »
if i could get an early rochester quadrajet onto one of these engines easy i would!

Offline TwoTired

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Re: 74 cb 550.... Another carb question.. # of turns for these screws (UPDATED)
« Reply #30 on: December 21, 2013, 10:36:47 AM »
The carb's pilot circuits do not have throttle linked regulation, per se.  They deliver mixture according to the carb throat pressure present at the exit ports.   As long as the engine is providing suction, they will deliver at a rate commensurate with that suction, at any throttle selection.

However, the volume produced by the pilot circuit is the minimum requirements + some for the engine to operate at idle with little to no power produced from the engine.

Consider it like the allowance you got as a kid compared to the enormous salaries you now get as an adult.  It wouldn't pay the bills during high demand expenses.  But, it might pay for a movie visit, if you still got the same allowance today while you are pulling that full financial load.

The vacuum level present in the carb duct is highly affected by the duct work parameters both preceding and downstream from the jet exit port location.  This is why a partially clogged filter, other upstream restriction, or a vacuum leak downstream the ports have such an effect on mixture delivery.
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline Jimsun

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Updated regarding a cb550 carb rebuild kit.

Im asking for your opinion,advise, and experience. I need it for 1 needle,main and slow jet. Im planning to resell the rest to even up ftom the purchase.

http://bit.ly/1l40wHT
74 cb550

Offline TwoTired

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Re: 74 cb 550.... Another carb question.. Rebuild kit from ebay (updatedx2!!)
« Reply #32 on: January 02, 2014, 12:01:04 PM »
Those are K&L aftermarket kits stated to fit the 74 model carbs.  They will fit and -should- work.  But, whether the part dimensions are really to the same factory dimension and tolerance as factory parts is dependent on the manufacturers diligence and QA checks made to the part.
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline flybox1

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Re: 74 cb 550.... Another carb question.. Rebuild kit from ebay (updatedx2!!)
« Reply #33 on: January 02, 2014, 12:15:54 PM »
might be a good idea making the same change in all carbs, not just in the one needing attention.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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