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Author Topic: CB550 Main Jets too small ?  (Read 2303 times)

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grapppa

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CB550 Main Jets too small ?
« on: January 18, 2006, 10:19:49 AM »
Well gang, last night (member) "Dennis" and I took a look at by disassembled carbs for my 74 CB550/4.  The bike has been running rich (sooty plugs) and coughing and hesitating over 4K rpm under load.  This was the second time I completely disassembled and cleaned all components.  OK... So I pull out a main jet and the number on them are (keihin) "75"  NOT  "100" as per what the specs call for.  The needles are set on the second notch from the top indicating lean.  We speculated that someone was trying to compensate for an over rich condition that may have been caused by leaking seals on the mains as the o-rings were likely not sealing correctly due to corrosion/wearing away of the jet holding metal.  This problem has been corrected by replacing the carb bodies and rebuilding the entire carb.   I happen to have a set of 98's from a 76 CB550 SS that I am going to replace them with unless I hear otherwise from you guys !
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Offline bistromath

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Re: CB550 Main Jets too small ?
« Reply #1 on: January 18, 2006, 03:53:13 PM »
No way you should be running 75's on that unless your exhaust is a soda straw. Try the 98s. Are you running the stock airbox and exhaust?
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'75 CB550F

Offline TwoTired

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Re: CB550 Main Jets too small ?
« Reply #2 on: January 18, 2006, 04:04:24 PM »
75s might be fine if they've been (cough) drilled.


Cheers,
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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.

grapppa

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Re: CB550 Main Jets too small ?
« Reply #3 on: January 18, 2006, 06:41:38 PM »
Yes I am running stock exhaust and airbox.  No, they have not been drilled - there is a very perceptible difference in openings between the 75s and 98s.
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grapppa

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Re: CB550 Main Jets too small ?
« Reply #4 on: January 21, 2006, 07:41:16 AM »
Gentlemen,
After long months of tweaking, repairing, searching, assembling and disassembling I can now say that my CB550/4 is now operating well.  Not 100%, but the problems that I had with hesitation was largely due to the incorrect main jets.   All 4 cyl are firing and the bike pulls right up to 8000K.  Woohoo, to say the least.
Nevertheless, the quest for perfection is still on, and the tweaking, etc will continue.  But I would like to thank all of those, esp. Dennis, for helping me in my quest.
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Offline Bob Wessner

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Re: CB550 Main Jets too small ?
« Reply #5 on: January 21, 2006, 08:02:50 AM »
Quote
the quest for perfection is still on, and the tweaking, etc will continue

Isn't this one of those never ending things? We complain about it, but actually enjoy the pursuit?  ;)
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We'll all be someone else's PO some day.
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